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NATURAL GAS
HYDRATES
A Guide for Engineers
Fourth Edition

JOHN CARROLL
Gas Liquids Engineering, Calgary, Canada
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This book is dedicated to my beautiful wife Ying (Alice) Wu, who I love
deeply. She is a constant source of inspiration to me.
Preface to the fourth edition

Natural gas hydrates continue to be problematic in the production,

transportation, and processing of natural gas. Companies spend millions of
dollars attempting to mitigate problems that arise from these ice-like solid
materials. The purpose of this book is twofold. First is to provide the reader
with an understanding of these mysterious compounds. Second is to
provide the tools necessary to combat their formation or to remedy the
situation when they form.
The book structure is similar to the previous edition, but there are
several new sections and subsections. There are new topics discussed in
almost every chapter. Many of these ideas come from people who have
attended my one-day course on hydrates.
On a personal level, I find hydrates to be fascinating and studying them
is truly rewarding. There are always new discoveries and deeper research
into their behavior.
As with past editions, the fourth edition of this book is intended for
engineers. However, others who have to deal with hydrates will find some
value in the material presented. It is not really a book for researchers but
more directed to people in the field who must confront these pest materials.

xi
Preface to the third edition

The objective of the third edition is the same as the first twodto give
engineers in the field the concepts to understand hydrates. From this
understanding they should be able to implement strategies to prevent them
from forming and to combat them when they form. Gas hydrates continue
to be a significant concern in the natural gas business. Companies spend
millions of dollars attempting to mitigate problems that arise from these
ice-like solid materials.
With each new edition there are new discoveries to explore; new
concepts to examine. Although the chapter structure remains unchanged
from the Second Edition, there are several new topics included in almost
every chapter. Most of these ideas come from people who have attended
my one-day course on hydrates.
For the author, hydrates remain a continuing interest because of their
unusual properties and new discoveries. This makes them an engaging
research topic. But as a process engineer, they remain a concern in my daily
work as they are for many other engineers.
Although the book is intended for engineers, others who have to deal
with hydrates will find some value in the material presented.

xiii
Preface to the second edition

The goal of the second edition is the same as the firstdto provide prac-
ticing engineers the tools to deal with hydrates.
One of the reasons that the author finds hydrates so interesting is their
unusual properties. Since the time of the first edition several new properties
have come to light and are discussed in the second edition. These include
the type of hydrate formed from mixtures of methane and ethane, hydrates
of hydrogen, the role of isopropanol in hydrate formation, etc. All of these
topics will be discussed.
Another addition to the book is discussion of a few other hydrate
formers. Notably, the hydrates of ethylene and propylene are included.
More examples are taken from the literature and additional comparisons
are made. A new section on the prediction of hydrate formation in sour gas
is also included.

xv
Preface to the first edition

Gas hydrates are of particular interest to those working in the natural gas
industry. Thus the main audience for this book is the engineers and
scientists who work in this field. Provided in this book are the tools for
predicting hydrate formation and details on how to combat them.
The reason for the genesis of this book was a one-day course presented
to engineers who work in the natural gas business. In particular, these
companies produce, process, and transport natural gas. The book has been
expanded from the original set of class notes. Much of the new material
came from feedback from attendees.
Many people outside the field of natural gas have also attended the
course and found some value in the material. These include oceanographers
studying the hydrate deposits on the seabeds throughout the world.
Astronomers investigating the possibility of hydrates on the planets of the
solar system as well as other celestial bodies may also find some of the
material in this book of some use. And those who are simply curious about
these interesting compounds will find this book to be useful.
The structure of the book is a little unusual. The chapters are meant to
be approximately independent; however, they do follow from the more
simple introductory topics to the more advanced applications. Occasionally
it is necessary to take a concept from a subsequent chapter in order to make
a point in the current chapter. This is unfortunate, but it is also necessary.
The purpose of this book is to explain exactly what gas hydrates are,
under what conditions they form, and what can be done to combat their
formation. Another purpose of this book is to explore some of the myths
associated with gas hydrates. The material is organized and presented in
such a way that the average engineer can use the information in their
day-to-day work.
In some sections of the book, especially those dealing with dehydration,
pipeline heat loss calculations, and lineheater design, the reader would
benefit greatly if they have the ability to calculate the physical properties of
natural gas. The properties of natural gas are not covered in this book.

xvii
Acknowledgments

There are many people whom I must thank. Without their help and
support, this book would not have been possible.
First, I would like to thank my employer Gas Liquids Engineering Ltd.,
Calgary, Alberta, Canada, and in particular the principals of the company
Douglas MacKenzie and James Maddocks. They allowed me the time to
build the hydrates course upon which this book is based and provided me
the time to write the manuscript. I would also like to thank them for the
other resources they provided. This book would have been impossible
without them. I would also like to thank my colleague Peter Griffin, also
from Gas Liquids Engineering, for his encouragement. With his help I have
been able to present this material throughout the world.
Words cannot express my thanks to Alan E. Mather of the University of
Alberta, Edmonton, Alberta, Canada. He was my patient supervisor during
my time as a graduate student, and he continues to be my mentor. The core
of my knowledge of thermodynamics, and in particular how it relates to
phase equilibrium, is a result of his teaching. Over the years we have
collaborated on many interesting projects. In addition, he proofread early
versions of the manuscript, which was enormously valuable.
The book is the result of a one-day course on gas hydrates that I
conducted. I have received positive feedback from many of those who
attended. Some of their ideas have been added to the book. Thus, I thank
all of those who attended the course. Many of the additions to the book are
a direct result of feedback from attendees.
I would be amiss if I did not also thank my loving wife, Ying Wu, for
her endless support, encouragement, and love.
I would like to express my gratitude to the Gas Processors Association
(GPA) and the Gas Processors Suppliers Association (GPSA), both of Tulsa,
Oklahoma, for permission to reproduce several figures from the GPSA
Engineering Data Book (11th ed.). Furthermore, over the years these associ-
ations have sponsored a significant amount of research into gas hydrates. This
research has been valuable both to the author of this book and others
working in the field.
The author would also like to thank the Center for Hydrates Research
at the Colorado School of Mines in Golden, Colorado and its Director
Dr. Carolyn Koh and Director Emeritus Dr. E. Dendy Sloan. The Center is

xix
xx Acknowledgments

a source of primary research into hydrates including experimental work,

theoretical models, and software development. Their work is noted
throughout this book. In particular, the Center for Hydrates Research,
through Dr. Koh, has given this author permission to use their software
CSMHYD and CSMGEM and to reproduce screen captures from them. I
am very grateful for this access.
I would also like to thank my friend Prof. Robert Marriott at the
University of Calgary, Calgary, Alberta. Prof. Marriott’s lab has expanded
into the field of hydrates, making some important measurements some of
which are reported here. Prof. Marriott is also a leader in the field of
measuring water content of gas mixtures; a subject important to gas hy-
drates. I have enjoyed our many conversations regarding these subjects.
CHAPTER 1

Introduction

This chapter is an attempt to introduce hydrates, without much back-

ground material. Many of the words and principles will be better defined in
subsequent chapters of this book. However, they are needed here to present
the basic introductory concepts. If you are a little confused as you read this
chapter, hopefully things will become clearer as you progress through the
book.
Let’s begin with the main focus of the book, hydrates. In its most
general sense, a hydrate is a compound containing water. For example,
there is a class of inorganic compounds called “solid hydrates.” These are
ionic solids where the ions are surrounded by water molecules and form
crystalline solids. However, as used in this book, and commonly in the
natural gas industry, a hydrate is solid phase composed of a combination of
certain small molecules and water.
Hydrates are crystalline solid compounds formed from water and small
molecules, without water there are no hydrates and without the small
molecules that stabilize the structure there are no hydrates. They are a
subset of compounds known as clathrates or inclusion compounds.
A clathrate compound is one where a molecule of one substance is enclosed
in a structure built up from molecules of another substance. One type of
molecule is literally trapped in a cage composed of the molecules of a
different substance. Here water builds up the structure and the other
molecule resides within. The size of the other molecule must be such that it
can fit within the water structures. More details of the nature of these
structures formed by water and the molecules within are presented in
Chapter 2 of this book.
Although the clathrates of water, the so-called hydrates, are the focus of
this work, they are not the only clathrate compounds. For example, urea
forms interesting inclusion compounds as well.
Although hydrates were probably encountered by others earlier, credit
for their discovery is usually given to the famous English chemist, Sir
Humphrey Davy. He reported of the hydrate of chlorine in the early 19th
century. In particular, he noted (1) that the ice-like solid formed at
Natural Gas Hydrates
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2 Natural Gas Hydrates

temperatures greater than the freezing point of water and (2) that the solid
was composed of more than just water. When melted, the hydrate of
chlorine released chlorine gas.
Davy’s equally famous assistant, Michael Faraday, also studied the hy-
drate of chlorine. In 1823, Faraday reported the composition of the
chlorine hydrate. Although his result was inaccurate, it was the first time the
composition of a hydrate was measured.
Throughout the 19th century, hydrates remained basically an intellec-
tual curiosity. Early efforts focused on finding which compounds formed
hydrates and under what temperatures and pressures they would form.
Many of the important hydrate formers were discovered during this era.
Among the 19th-century, hydrate researches who deserve mention are
the French chemists Villard and de Forcrand. They measured the hydrate
conditions for a wide range of substances, including hydrogen sulfide.
The first crystallographic studies of gas hydrates were published by von
Stackelberg from the University of Bonn in Germany in the 1940s and 50s.
Von Stackelberg and his group established that there were two distinct
types of hydrate crystal structures. We will discuss these hydrate types in
Chapter 2.
However, it would not be until the 20th century that the industrial
importance of gas hydrates would be established, especially for the natural
gas industry (Hammerschmidt, 1934).
Over the years, there have been many, many experimental studies of
hydrate formation. These include the hydrates for single components,
binary mixtures, and multicomponent mixtures. Some of these studies are
discussed in the chapters that follow. If the reader has doubts about methods
used in the work, they should consult the literature. They may not find the
exact data for their situation, but they may find data which are useful for
testing the models they chose to employ.

1.1 What is water?

This may seem like a strange question, but it is more complicated than you
might think. Many of the terms used in this book will no doubt cause
confusion, and it might be surprising that water is one of them. Some of the
confusion arises from the English language and our, sometimes my, use of
it. For example, we can define water as “a colorless, transparent, odorless
liquid,” which is probably what most people think when they hear the
word and a typical dictionary definition. But it could be defined as
 Introduction 3

“a chemical compound made up of hydrogen and oxygen with the formula

H2O (regardless of the phase it is in),” which is a more general definition
but sounds more like a chemist. In this book I will use the term aqueous
liquid to mean water in the liquid phase and hopefully avoid this confusion.
In addition, in this book, the term water will be used in the chemical sense,
that is, a compound made from two hydrogen atoms and one oxygen atom.
If the water is pure or nearly so and exists in the vapor phase, we call this
“steam.” If the gas contains water but the water is dilute, such as in the air,
we usually refer to this as “moisture.” This further leads to terms like
“moisture content,” how much water is in the gas, “moisture measure-
ment,” and moisture analyzer, a device used to measure the moisture
content.
We also have the terms humidity, which refers to the amount of water
in a gas, again typically the air, and relative humidity. So if the air is 50%
relative humidity, it contains only half the water it can hold. The relative
humidity is a function of the temperature and the pressure.
The general term for solid water in the pure state is ice. However, if you
think about it, we have many terms for solid water depending upon its
physical nature, such as frost, snow, hail, glacier, etc.
Hydrate is not ice, but it is ice-like, similar in appearance and physical
properties. But a hydrate is a solution composed of water and other
components, whereas ice is pure water.
However, the term frost point is the temperature where a solid first
appears whether it is ice or hydrate or some other solid. So if one cools a gas
stream isobarically until a solid forms, that is the frost point temperature
regardless of whether or not the solid is ice or hydrate.

1.2 Natural gas

Although all terrestrial gases (air, volcanic emissions, swamp gas, etc.) are
natural, the term “natural gas” is customarily reserved for the mineral gases
found in subsurface rock reservoirs. These gases are often associated with
crude oil. Natural gas is a mixture of hydrocarbons (such as methane,
ethane, propane, etc.) and a few nonhydrocarbons (hydrogen sulfide,
carbon dioxide, nitrogen, etc.) and water.
The light hydrocarbons in natural gas have value as fuels and as feed-
stock for petrochemical plants. As a fuel, they are used for heating and
cooking in private homes, to generate electricity, and increasingly as fuel for
motor vehicles. In the chemical plants, they are converted to a host of
4 Natural Gas Hydrates

consumer products, everything from industrial chemicals, such as methanol,

to plastics, such as polyethylene.
The nonhydrocarbons tend to be less valuable. However, depending
upon the market situation, hydrogen sulfide has some value as a precursor
to sulfur. Sulfur in turn has several applications, the most important of
which is probably the production of chemical fertilizer. Carbon dioxide and
nitrogen have no heating value and thus are useless as fuels.
Natural gas that contains significant amounts of sulfur compounds, and
hydrogen sulfide in particular, is referred to as “sour.” In contrast, natural
gas with only minute amounts of sulfur compounds is called “sweet.”
Unfortunately, there is no strict defining sulfur content that separates sour
gas from sweet gas. As we have noted, sales gas typically contains less than
about 15 ppm and is indeed sweet, but for other applications there are other
definitions. For example, in terms of corrosion, the sweet gas may contain
more sulfur compounds and not require special materials.
Strictly speaking, gas that contains carbon dioxide but no sulfur com-
pounds is not sour. However, gas that contains carbon dioxide shares many
characteristics with sour gas and is often handled in the same way. Probably,
the most significant difference between carbon dioxide and hydrogen
sulfide are the physiological properties and this is what really separates the
two. Hydrogen sulfide is highly toxic, whereas carbon dioxide is essentially
nontoxic, except at very high concentrations. Furthermore, hydrogen
sulfide has an obnoxious odor while carbon dioxide is odorless.

1.2.1 Sales gas

An arrangement is made between the company producing the natural gas
and the pipeline company for the quality of the gas the purchaser will
accept. Limits are placed on the amounts of impurities, heating value,
hydrocarbon dew point, and other conditions. This arrangement is what
defines “sales gas.”
Among the impurities that are limited in the sales gas is water. One of
the reasons why water must be removed from natural gas is to help prevent
hydrate formation.
In terms of water content, a typical sales gas specification would be less
than approximately 10 lb of water per million standard cubic feet of gas
(10 lb/MMCF). In the United States, the value is usually 7 lb/MMCF,
whereas in Canada it is 4 lb/MMCF and other jurisdictions have other
values. For those who prefer SI units, 10 lb/MMCF is equal to 0.16 grams
 Introduction 5

per standard cubic meter (0.16 g/Sm3) or 160 milligrams per standard cubic
meter (160 mg/Sm3). More discussion of units and standard conditions is
presented later in this chapter.
There are several other restrictions on the composition of sales gas. For
example, there is a limit on the amount of hydrogen sulfide present
(typically on the order of about 10 parts per million or 10 ppm) and the
amount of carbon dioxide (typically around 2 mole percent). These too
vary from jurisdiction to jurisdiction, contract to contract.

1.2.2 Hydrates
In combination with water, many of the components commonly found in
natural gas form hydrates. One of the problems in the production, pro-
cessing, and transportation of natural gas and liquids derived from natural
gas is the formation of hydrates. Hydrates cost the natural gas industry
millions of dollars annually. In fact, individual incidents can cost $1,000,000
or more depending upon the damage inflicted. There is also a human price
to be paid because of hydrates. Sadly, there have been deaths either directly
or indirectly associated with hydrate and their mishandling.
However, the importance of natural gas hydrates was not apparent in
the early era of the gas business. In the early era of the natural gas business,
gas was produced and delivered at relatively low pressure. Thus, hydrates
were never encountered. In the 20th century, with the expansion of the
natural gas industry, the production, processing, and distribution of gas
became high-pressure operations. Under pressure, it was discovered that
pipelines and processing equipment were becoming plugged with what
appeared to be ice, except the conditions were too warm for ice to form. It
was not until the 1930s that Hammerschmidt (1934) clearly demonstrated
that the “ice” was actually gas hydrates. And that the hydrates were a
mixture of water and the components of natural gas.
In the petroleum industry, the term “hydrate” is reserved for substances
that are usually gaseous at room temperature. These include methane,
ethane, carbon dioxide, and hydrogen sulfide. This leads to the term “gas
hydrates” and also leads to one of the popular misconceptions regarding
these compounds. It is commonly believed that nonaqueous liquids do not
form hydrates. However, liquids may also form hydrates. An example of a
compound that is liquid at room conditions, yet forms a hydrate, is
dichlorodifluoromethane (Freon 12). But we are getting ahead of ourselves.
6 Natural Gas Hydrates

More details about what compounds form hydrates will be given in

Chapter 2.
One of the iconic images of a hydrate is the “ice on fire”dburning of a
hydrate. Because the hydrate is composed of both host (water) and guest, as
the hydrate melts the guest is released. With a methane hydrate or a natural
gas hydrate, sufficient hydrocarbon is released such that it can be lit on fire.
Fig. 1.1 is a photograph showing the ice on fire. It is important to note that
not all hydrates can be ignited. Only those that contain a sufficient amount
of hydrocarbon can be set on fire. For example, try as you may you will
never be able to ignite a carbon dioxide hydratedCO2 does not burn.

1.3 The water molecule

Many of the usual properties of water (and yes, if you are not aware of it,
water does have some unusual properties) can be explained by the structure
of the water molecule and the consequences of this structure.
Of particular interest to us is the fact that the structure of the water
molecule leads to the possibility of hydrate formation. In the next sections,
it will be demonstrated that water does indeed have some unusual
properties.

Figure 1.1 Iconic “Ice on Fire” picture showing a methane hydrate burning. (Credit: J.
Pinkston and L. Stern (USGS), USGS. Public domain.)
 Introduction 7

1.3.1 The normal boiling point of water

As an example of the unusual properties of water, consider the boiling
point. We will use some simple chemistry to demonstrate that the boiling
point of water is unusually high. The boiling points used in this discussion
are taken from Dean (1973).
The periodic table of elements is not just a nice way to display the
elements. The original design of the table came from aligning elements
with similar properties. Thus, elements in the rows of the tables have similar
properties or at least properties that vary in a periodic, predictable manner.
The 6A column in the table consists of oxygen, sulfur, selenium, and
tellurium. We would expect these elements and their compounds to have
similar properties, or at least to behave in a predictable pattern.
The hydrogen compounds of the column 6A elements are water
(hydrogen oxide), hydrogen sulfide, hydrogen selenide, and hydrogen
telluride. All have the chemical formula H2X, where X represents the
group 6A element. If we look at the normal boiling points of H2S, H2Se,
and H2Te, we should be able to predict the boiling point of water. Fig. 1.2
0

hydrogen telluride

-10

-20
Normal Boiling Point (°C)

-30

-40
hydrogen selenide

-50

-60
hydrogen sulfide

-70

water?
-80
10 20 30 40 50 60 70 80 90 100 110 120 130 140 150
Molar Mass (kg/kmol)
Figure 1.2 The normal boiling points of hydrogen compounds.
8 Natural Gas Hydrates

shows a plot of the normal boiling points for these three compounds. Note
that as the size of the molecule increases, so does the normal boiling point.
Although it is not exactly linear, we can use a linear approximation to
estimate the boiling point of water. This extrapolation yields an estimated
boiling point of
74 C! As the boiling point of water is 100 C, this is
clearly a very poor estimation. There is probably something unusual about
water.
It is worth noting that a similar plot could be constructed showing the
melting points for these compounds. Again the predicted melting point of
water, based on the other substances, is much too low.
As a second example, consider the homologous series of normal alco-
hols. Fig. 1.3 shows a plot of the normal boiling points of the alcohols as a
function of their molar mass (molecular weight). In this case, the relation is
nearly linear. Assume that water is the smallest member of this group of
compounds, and extrapolate the correlation to estimate the boiling point.
This yields 43 C for the boiling point, which is significantly lower than the
actual value.

140
n-pentanol
130

120

n-butanol
110
Normal Boiling Point (°C)

100
water
n-propanol
90

80
ethanol
70

60 methanol

50

40
10 20 30 40 50 60 70 80 90 100
Molar Mass (kg/kmol)
Figure 1.3 The normal boiling points of alcohols.
 Introduction 9

Why does water have such an anomalously large boiling point?

1.3.2 Enthalpy of vaporization

In Table 1.1, the enthalpies of vaporization of several components at their
boiling point are listed. Admittedly, it is a small list, but the table includes
both polar and nonpolar substances. From this table it can be seen that
water has a fairly large enthalpy of vaporization, even in comparison to
other polar substances.
It takes significantly more energy to boil 1 kg of water than it does to
boil any of the hydrocarbons listed in the tabledapproximately 5 times as
much energy.
Again, we must ask the question, why does water behave so
anomalously?

1.3.3 Expansion upon freezing

Another unusual property of water is that it expands upon freezing. In
common terms, this means that ice floats on water. In engineering terms,
the density of ice (917 kg/m3 or 57.2 lb/ft3) is less than that of liquid water
(1000 kg/m3 or 62.4 lb/ft3) at the freezing point.

Table 1.1 The enthalpy of vaporization of several substances at their normal boiling
point.
Compound Nature Enthalpy of vaporization (kJ/kg)
Water Polar 2257
Methanol Polar 1100
Ethanol Polar 855
Acetone Polar 521
Ethylene glycol Polar 800
Ammonia Polar 1369
Methane Nonpolar 510
n-pentane Nonpolar 357
n-octane Nonpolar 306
Benzene Nonpolar 394
o-xylene Nonpolar 347
Cyclohexane Nonpolar 358
Data taken from Dean, J.A. (ed.), 1973. Lange’s Handbook of Chemistry, eleventh ed. McGraw-Hill,
New York, NY, pp. 9e85 to 9e95.
10 Natural Gas Hydrates

The simple reason for this expansion is that the water atoms arrange
themselves in an ordered fashion and the molecules in the crystal occupy
more space than those in the liquid water. The reason for this behavior is
also because of the shape of the water molecule and something called the
hydrogen bond.
The molecules in solid water form a hexagonal crystal. This is most
obvious in snow with its characteristic pattern structures (see for example
Fig. 1.4).

Figure 1.4 Microphotographs of ssnowflakes. (Courtesy of the National Oceanic and

Atmospheric Administration (NOAA), Washington, DC e http://www.photolib.noaa.gov.
Original photographs by Wilson Bentley (1865e1931), which were not copyright.)
 Introduction 11

1.3.4 The shape of the water molecule and the hydrogen

bond
Virtually all of the unusual properties of water noted earlier can be
explained by the shape of the water molecule and the interactions that
result from its shape.
The water molecule consists of a single atom of oxygen bonded to two
hydrogen atoms, as depicted in Fig. 1.5. In the water molecule the bond
between the oxygen and hydrogen atoms is a covalent bond. A covalent
bond is essentially a shared pair of electrons. The angle between the two
hydrogen atoms in the water molecule is about 105 degrees.
What Fig. 1.5 does not show is that there are two pairs of unbonded
electrons on the “back” of the oxygen molecule. These electrons induce
negative charges on the oxygen molecule and a small positive charge on the
hydrogen atoms. The induced electrostatic charges on the molecule
(denoted dþ for the positive charge and d
for the negative) are shown in
Fig. 1.5A. Thus, the water molecules will tend to align with a hydrogen
molecule lining up with an oxygen.

Figure 1.5 The shape of the water molecule. (A) Stick representation showing induced
charges, which result in hydrogen bonding, and (B) ball model showing the angle
between the hydrogen molecules.
12 Natural Gas Hydrates

This aligning of the hydrogen and oxygen atoms is called a “hydrogen

bond.” The hydrogen bond is essentially an electrostatic attraction between
the molecules. It should be noted that each water molecule has two pair of
unbond electrons and thus has two hydrogen bondsdtwo water molecules
“stick” to each water molecule. The hydrogen bond is only 1/10 or 1/20 as
strong as a covalent bond, which is what holds the oxygen and hydrogen
atoms together in the water molecule, but this is still strong enough to
explain the properties discussed earlier.
The hydrogen bonds are particularly strong in water, although they are
present in other substances, such as the alcohols discussed earlier. It is for this
reason that the normal boiling points of the alcohols are significantly larger
than their paraffin analogues.
When the water molecules line up, they form a hexagonal pattern. This
is the hexagonal crystal structure discussed earlier. From elementary ge-
ometry, it is well know that the angle between the sides of a regular
hexagon is 120 degrees, which is greater than the 105 degrees angle in the
water molecule. This seeming paradox is overcome because the hexagonal
pattern of the water molecules is not planar. The hexagonal pattern of the
water molecules in the ice crystal is shown in Fig. 1.6. In this figure the
circles represent the water molecules and the lines the hydrogen bonds.

1.4 Hydrates
It is a result of the hydrogen bond that water can form hydrates. The
hydrogen bond causes the water molecules to align in regular orientations.
The presence of certain compounds causes the aligned molecules to stabilize
and a solid mixture precipitates.
The water molecules are referred to as the “host” molecules and the
other compounds, which stabilize the crystal, are called the “guest” mol-
ecules. In this book the guest molecules are more often referred to as

Figure 1.6 The three-dimensional hexagonal arrangement of the water molecules in

an ice crystal.
 Introduction 13

“formers.” The hydrate crystals have complex, three-dimensional structures

where the water molecules form a cage and the guest molecules are
entrapped in the cages.
The stabilization resulting from the guest molecule is postulated to be
due to van der Waals forces, which is the attraction between molecules that
is not as a result of electrostatic attraction. As described earlier, the hydrogen
bond is different from the van der Waals force because it is due to strong
electrostatic attraction, although some classify the hydrogen bond as a van
der Waals force.
Another interesting thing about gas hydrates is that there is no bonding
between the guest and host molecules. The guest molecules are free to
rotate inside the cages built up from the host molecules. This rotation has
been measured using advanced chemical techniques such as spectroscopic,
diffraction, etc. Therefore, these compounds are best described as a solid
solution.
The formation of a hydrate requires the following three conditions:
1. The right combination of temperature and pressure. Hydrate formation
is favored by low temperature and high pressure.
2. A hydrate former must be present. Hydrate formers include methane,
ethane, and carbon dioxide.
3. A sufficient amount of waterdnot too much, not too little.
Fig. 1.7 gives a visual of the three criteria for hydrate formation. The
three are interconnecteddviolate one and a hydrate does not form.

Figure 1.7 Simplified diagram of the three criteria for hydrate formation.
14 Natural Gas Hydrates

Although this figure gives a quick visual image, it lacks the detail provided
by the discussion presented earlier. However, it provides a useful visual.
These three points will be examined in some detail in subsequent
chapters, but they deserve a few comments at this point. As was noted, low
temperature and high pressure favor hydrate formation. The exact tem-
perature and pressure depends upon the composition of the gas. However,
hydrates form at temperatures greater than 0 C (32 F), the freezing point of
water. The nature of hydrate formers is discussed in detail in Chapter 2.
To prevent hydrate formation, one merely has to eliminate one of the
three conditions stated above. Typically we cannot remove the hydrate
formers from the mixture. In the case of natural gas, it is the hydrate formers
that are the desired product. So we attack hydrates by addressing the other
two considerations.
Other phenomena that enhance hydrate formation include the
following:
1. Turbulence
a. High velocity
Hydrate formation is favored in regions where the fluid velocity
is high. This makes choke valves particularly susceptible to hydrate
formation. First, there is usually a significant temperature drop
when natural gas is choked through a valve due to the Joulee
Thomson effect. Second, the velocity is high through the narrowing
in the valve.
b. Agitation
Mixing in a pipeline, process vessel, heat exchanger, etc., en-
hances hydrate formation. The mixing may not be due to an actual
mixer but perhaps a tortuous routing of the line.
2. Nucleation sites
In general terms, a nucleation site is a point where a phase transition
is favored, and in this case the formation of a solid from a fluid phase. An
example of nucleation is the deep fryer used to make French fries in fast-
food restaurants throughout the world. In the fryer the oil is very hot
but it does not undergo the full rolling boil because there are no suitable
nucleation sites. However, when the potatoes are placed into the oil, it
vigorously boils. The French fries provide an excellent nucleation site.
Good nucleation sites for hydrate formation include an imperfection
in the pipeline, a weld spot, or a pipeline fitting (elbow, tee, valve, etc.).
Corrosion by-products, silt, scale, dirt, and sand all make good nucle-
ation sites as well.
 Introduction 15

3. Free water
No, this is not a contradiction to earlier statements. Free water is not
necessary for hydrate formation, but the presence of free water certainly
enhances hydrate formation.
The presence of free water also assures that there is plenty of water
present, which is more likely to form a plug.
In addition, the wateregas or the watereoil interface is a good
nucleation site for hydrate formation.
The items in the above list enhance the formation of a hydrate, but are
not necessary. Only the three conditions given earlier are necessary for
hydrate formation.
Another important aspect of hydrate formation is the accumulation of
the solid. The hydrate does not necessarily agglomerate in the same location
as it is formed. In a pipeline, the hydrate can flow with the fluid phase,
especially the liquid. It would tend to accumulate in the same location as
the liquid does. Usually it is the accumulations of the hydrates that cause the
problems. In a multiphase pipeline, it is the accumulations that block line
and plug and damage equipment.
Often pigging is sufficient to remove the hydrate from the pipeline.
Pigging is the process of inserting a tool (called a “pig”) into the line.
Modern pigs have many functions, but the main one remains pipeline
cleaning. The pig fits tightly into the line and scraps the inside of the pipe. It
is transported along the line with the flow of the fluid and by doing so it
removes any solids (hydrate, wax, dirt, etc.) from inside the line. The
pigging can also be used to remove accumulations of liquids.
However, the pigging must be scheduled such that the accumulations of
hydrates do not become problematic. Usually pigging is not used to clean
hydrates from a line. Other measures are more commonly used to deal with
hydrates and these are detailed in subsequent chapters of this book.
Another benefit of pigging is the removal of salt, scale, etc., which is
important for the proper operation of a pipeline. It also means that potential
nucleation sites for hydrate formation are removed.

1.4.1 Temperature and pressure

As was noted earlier, hydrate formation is favored by low temperature and
high pressure. For each gas it is possible to generate a hydrate curve that
maps the region in the pressureetemperature plane where hydrates can
form. Much of the rest of this book is dedicated to the tools used to predict
16 Natural Gas Hydrates

this locus. Again, without getting to far ahead of ourselves, some pre-
liminary discussion of hydrate curves is appropriate.
Fig. 1.8 shows a typical hydrate curve (labeled “hydrate curve”). The
region to the left and above this curve (high pressure, low temperature) is
where hydrates can form. In the region to the right and below the hydrate
curve, hydrates can never formdin this region, the first criterion is violated.
Therefore, if your process, pipeline, well, etc., operates in the region
labeled “no hydrates,” then hydrates are not a problem. On the other hand,
if it is in the region labeled “hydrates region,” then some remedial action is
required to avoid hydrates.
It might seem as though we can treat the temperature and pressure as
separate variables but when discussing hydrates, they are linked. For
example, you cannot say “A hydrate will not form at 10 C for the gas
mixture shown in Fig. 1.8.” You must qualify this with a pressure. So at
10 C and 5 MPa, the process is in the “hydrate region,” whereas at 10 C
and 1 MPa, the process is in the region where a hydrate will not form.
Thus, we must talk about a combination of temperature and pressure and
not each variable on its own.

14

12

10
hydrate region
Pressure (MPa)

4 hydrate curve

plus 3 Celsius
2

no hydrates
0
0 5 10 15 20 25
Temperature (°C)
Figure 1.8 Pressureetemperature diagram showing the hydrate region, the region
with no hydrates, and a safety margin.
 Introduction 17

Furthermore, it is common to add a margin of safety, even to the best

hydrate prediction methods. This margin can be 3 to 5 Celsius degrees (5 to
10 Fahrenheit degrees), but typically 3 Celsius degrees is used. The author
typically uses 3 Celsius degrees but the reader may have their own margin
or perhaps there is one specified by their company. A margin of safety is
shown in Fig. 1.8 (“plus 3 Celsius”) and the buffer zone between the
estimated hydrate curve and the þ3 Celsius curve is noted.
Throughout the remainder of the book, usually only the calculated
hydrate curves will be shown but the user should keep this safety margin in
mind.

1.5 Water and natural gas

Water is often associated with natural gas. In the reservoir water is always
present. Thus, produced natural gas is always saturated with water. In
addition, formation water is occasionally produced along with the gas. As
the temperature and pressure change during the production of the gas,
water can condense out. Methods for estimating the water content of
natural gas are presented in Chapter 10.
In addition, water is often involved in the processing of natural gas. The
process to sweeten natural gas (i.e., to remove hydrogen sulfide and carbon
dioxide, the so-called “acid gases”) often employs aqueous solutions. The
most common of these processes involve aqueous solutions of alkanol-
amines. The sweet gas (i.e., the product of the sweetening process) from
these processes is saturated with water.
There are several processes that are designed to remove water from
natural gas. These will be discussed in Chapter 6 of this book.
This association of water and natural gas means that hydrates will be
encountered in all aspects of the production and processing of natural gas.
A large portion of this book is dedicated to the prediction of the
conditions at which hydrates will form. Armed with this knowledge, en-
gineers working in the natural gas industry know whether or not hydrates
will be a problem in their application.
Once it has been determined that hydrates are a problem, or potentially
a problem, what can be done? Another large segment of this book addresses
this topic.
18 Natural Gas Hydrates

1.5.1 Free-water
There is a myth in the natural gas industry that “free water” (i.e., an
aqueous phase) must be present to form a hydrate. In subsequent sections of
this book, we will demonstrate that this is not correct. Free water certainly
increases the possibility that a hydrate will form, but it is not a necessity.
A strong argument demonstrating that free water is not necessary for
hydrate formation is presented in Chapter 9 on phase diagrams.
Another argument, the so-called “frost argument,” asks the simple
question: Is it necessary to have free water to form ice? The answer is no.
Frost forms without liquid water forming. The frost sublimes from the air
onto my car on winter nights. The water goes directly from the air to the
solid phase without a liquid being encountered. The airewater mixture is a
gas, and the water is not present in the air in a liquid form. If you have an
old-fashioned freezer, i.e., one that is not frost-free, just look inside. A layer
of frost builds without liquid water ever forming. Hydrates can “frost” via
the same mechanism.
One of the reasons why it is believed that free water is required for
hydrate formation is that hydrates formed without free water may not be
problematic. The inside of a pipe may “frost” with hydrates, but still
function properly. Or the amount of hydrate may be small and thus does
not plug lines or damage processing equipment. Such “frost” hydrates can
be easily cleaned using the pigging process discussed earlier.
The process of going directly from the gas to the solid is called subli-
mation and it is not that rare. For example, carbon dioxide sublimes at
atmospheric pressure. Solid CO2, commonly called “dry ice,” goes directly
from the solid to the vapor without forming a liquid. At atmospheric
pressure, CO2 goes directly from the solid to the vapor at a temperature of
about
78 C (
108 F). Another example of a solid that sublimes at at-
mospheric pressure is naphthalene, the main component of moth balls. The
reason why you can smell moth balls is because the naphthalene goes
directly from the solid to the vapor and it is the vapor that you can smell. In
reality, all pure substances sublime at pressures below their triple point
pressure and this includes pure water. So it should come as no surprise that
hydrates, under the right set of conditions, can sublime directly from the gas
phase to the solid phase.
 Introduction 19

1.6 Heavy water

Deuterium is an isotope of hydrogen. In the simple hydrogen molecule,
there is one proton, one electron, and no neutrons, protons, electrons, and
neutrons being the elementary particles that make up the atom. Deuterium,
on the other hand, is composed of one proton, one electron, and one
neutron. Because of the additional particle, deuterium is “heavier” than
normal hydrogen.
Water is composed of two hydrogen atoms and an oxygen atom. Heavy
water, also called deuterium oxide, is composed of two deuterium atoms
and an oxygen atom.
Now the question arises, does heavy water form a hydrate? The answer
is yes. Heavy water still exhibits hydrogen bondingdthe key to hydrate
formation. However, it requires slightly more pressure to form hydrates in
heavy water than in regular water (for example, see Chun et al., 1996).

1.7 The hydrate toolbox

What will be presented in this book are a set of tools for studying hydrates,
predicting the conditions at which they will form, preventing their for-
mation, and finally what to do when one occurs. These are the tools in our
hydrate toolbox.
We focus on two aspects of hydrates: (1) prevention and (2) remedia-
tion. What can we do to prevent hydrates from forming and what can we
do if a hazardous hydrate forms. Is it possible to have a benign hydrate?
The engineer must have a toolkit to combat hydrates. This includes
firmware (such as heaters), software to predict hydrate behavior, and in-
telligence to analyze the situation, interpret predictions, and apply the
correct measures. This book will address these items in more detail; in fact
this is the major theme of the book. However, an overview is provided
here.
First, the engineer should have the tools to predict hydrate formation.
Here we have split them into two broad categories: (1) hand calculations
and (2) computer-based. Although the hand calculation method seems
antiquated, they are still used in some circles and thus deserve discussion, in
particular the limited accuracy of these predictions. For the computer-based
applications, we will discuss the basis of the models as well as demonstrate
the accuracy of some of the commercial software packages.
Another random document with
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antelopes, buffaloes, and elephants. The latter, they say, the natives
do not kill, because they can get plenty of other meat, and they can
prevail on no one to buy the tusks. They destroy wild animals with
poisoned arrows, one of which they pretend to say will kill an
elephant in about an hour. They eat the flesh of the animal slain with
these arrows, but cut out and throw away the piece around the
poisoned wound. Yarro’s messenger has promised to show me the
tree from which they get the poison when we arrive at Wawa: they
tell a number of extravagant stories about its power and effects,
which are too ridiculous to believe.
In the evening I went to the place where the Houssa people were
encamped, in order to conclude my bargain with the taya, or head
man of the caravan, and to make him sign the written agreement in
Arabic by which he was to be bound to carry my baggage and
presents from Boussa to Kano; and for which I was to pay him, the
day after my arrival at the latter place, two hundred thousand
cowries. He had always fought off the agreement, saying, I could
conclude the bargain when I got over the river; that I must get the
sultan of Boussa to allow me to go, and then we should conclude the
bargain. I never could get him to say how much he would take them
for, or even that he would take them at all. I now said he must
determine, as, before I knew whether he would for certain take them
or not, it would be of no use asking the sultan of Boussa; “for if I get
the sultan’s leave, and you get me on the road, you may charge
what you please: if he does not allow me to go, signing the
agreement will do no harm, it will only be the loss of the papers. You
are mistaken if you think I have any thing to fear from the sultan of
Youri; I am a servant of the king of England, and will receive
assistance and protection whichever route I take.” He said he would
send for his partner. His partner came, Malem Mohamed, or the
learned Mohamed; a man that could not read or write, but could
repeat a chapter or two of the Koran by heart. He was a palavering
old rogue, who always repeated, to whatever the taya said, the
words “madealla, madealla,”—“very good, very good,”—without
giving any answer to what I asked. I told them, it did not require
much consideration about the matter: this must be done, yes or no,
before I see the sultan of Boussa; for if they did not determine
whether they would take my things or not, I would go direct to Youri.
The taya then said, how many loads would I have? I said, fifteen
bullocks or asses; that I would pay him at Kano, the day after my
arrival, as I could have what money I wanted from Hadji Hat Saleh
on giving him a receipt, as I had no money here; (not wishing to let
them know that I had a dollar here, as it might endanger my
existence and that of all my property). “Well,” says he, “I know you
can have what money you want from the merchants of Kano: I and
my partner will consider of the affair to-night, and give you an answer
to-morrow.” The taya returned with me to my encampment, and, to
my surprise, told me that I must not let it be known that I was going
to the Fellatas: “Say you are going to Bornou.” “So I am,” I said; “I
have got a letter for the sheikh, which I will show you to-morrow.”
When the taya left me, I began to think that what Yarro of Kiama had
told me was true. When I asked him to go with the caravan, says he,
“Are you a merchant? if you are, go with the caravan: if you are the
king of England’s messenger, you have nothing to do with them; your
way is to go from one king to another, not with caravans of
merchants. You will find plenty of people to put evil in your head; if
you are wise, do not believe them.”
Monday 20th.—At 6 A.M. left our encampment. Our road through
a woody country, rising into hill and dale, with some beautiful rocky
mounts, perched on the heights composed of blocks of sandstone
and clay ironstone; the soil a red clay and gravel. We halted at the
village of Barakina, where I stopped until the carriers came up. As I
arrived at this village, a hunter came in from the chase. He had a
leopard’s skin over his shoulder, a light spear in his hand, and his
bow and arrows slung over his shoulder. He was followed by three
cream-coloured dogs, a breed as if between the greyhound and cur:
they were adorned with round collars of different coloured leather.
The hunter and his dogs marched through the village as
independently as ever I saw a man, without taking the least notice of
us, or even looking at us. He was followed by a slave carrying a
dead antelope that he had killed this morning. They say the people
of Borgoo are the greatest hunters in Africa, and that the people of
this village and of those we have passed live entirely by the chase;
the little ground they cultivate being worked by the women.
 Leaving Barakina, and travelling until noon, I came to a rocky
ledge, formed like a wall, in some places rising into beautiful rocky
mounts with bold precipices, shaded on the top with trees of the
most luxuriant foliage. The road lay through a narrow pass in the
ledge, shaded with fine tall majestic trees. Here, I said to myself, is
the pass, or gates, leading to the Niger. The rocks of which the ledge
is composed are of a conglomerate, formed with large square pieces
of white quartz, imbedded in a shining dark gray substance; the
pieces of quartz about an inch square, the strata forming an angle of
about 40° with the zenith. At noon crossed the river Oli, which has a
very rocky bed, and is said to be impassable, from the swiftness of
the current, in the rainy season. At this place the rocks in the river
were a dark clay slate: its course was from west-north-west to east-
south-east. The head man of the village at the ferry told me that it
had its rise in the hills to the north of Niki, ran to the north of Kiama,
and entered the Quorra above Rakah. At the place where I and my
baggage crossed it was dry; but all other passengers, not being in
the service of a king, are required to cross at the ferry by a canoe,
where they have to pay ten cowries a head for each passenger, and
twenty cowries for a load for goods. After crossing, I halted at the
village of the ferry, which is called Billa, on the south side of the river.
I encamped under a shady tree for the superior coolness, though I
was offered the best house in the village. The head man brought me
a present of a sheep, some yams, milk and honey; and, a short while
after my arrival, the head man of the village of Barakina arrived with
a sheep, yams, and honey, making an apology for his not being at
home when I passed. Alligators are plenty in the river, as one of the
carriers, in going to bring water, was chased from the river side by
one: parrots, paroquets, and game abound near the banks of this
stream. In the evening it was reported to me that the whole of the
horses were lost: whether it be to extract a present or not, time will
show.
Tuesday, 21st.—It was 8 A.M. before the horses were brought
back. I sent all the baggage and stores off, except three boxes,
which I gave in charge to the head man of the village, who promised
to forward them to me at Wawa. I gave him and the head man of the
village of Barakina two yards of cloth each, with a knife and a few
beads, with which they were very well pleased. An escort of four
horsemen arrived to conduct me to Wawa, and at 8.30 A.M. I left
Billa and the escort, who had made the head man of the village
provide them with a breakfast. The road lay over a plain, well
cultivated, and planted with cottons, yams, and corn in a number of
places. At 10 halted under the shade of a tree, near the walls of
Wawa, until the escort came up, which they did in a short time
afterwards, when I proceeded with them into the town, to the gate of
the governor’s house, where I halted under a large spreading tree for
upwards of an hour. I then desired Yarro’s messengers to tell the
governor that if I was kept longer waiting outside I should return to
Kiama; that I was the king of England’s messenger, and would not
be kept outside of any door in this way. They went in and told the
governor, who sent out to say he was dressing to receive me, and
would be out immediately. In a few minutes a number of men came
out of the house, and sat down in two rows outside the door; then a
high stool was brought out, and placed in the entrance; after which
the great man came slowly out of the gate, with a long staff in his
hand, and seated himself on the stool. He sent for me. Until then I
had not dismounted. I went up and shook hands with him: he kept
his hand wrapped up in the sleeve of his tobe, for fear the touch of a
white kaffir should kill him. I told him at once who I was, and what I
wanted. He said, every thing I wished should be done, and as I must
be fatigued with my journey, I should see him again to-morrow. I was
shown to a very good house, but found it excessively hot: the
thermometer in the shade was 105° of Fahrenheit, which is higher
than it has been since I have been in Africa this time. In the
afternoon, the governor sent me a present of a goat, yams, honey,
and eggs, and the same from his head man.
I was not a little surprised, towards sunset, by a visit from the king
of Dahomey’s messengers. I thought that all my prospects were now
blasted; that they had been sent to detain me, and bring me back;
but my fears were soon allayed, by their saying that they were on
their way home; that they had heard white men had arrived here,
and they had come to pay their respects to me; that they had been in
Youri, and twelve months since had left Dahomey; that the king of
Dahomey had sent them to get a camel, but the war between the
people of Youri and the Fellatas prevented any camels coming to
Youri. These men brought two muskets to salute me with; they had
been here twelve days, and were intending to leave this for their own
country as soon as they could procure an answer from the governor.
I am lodged in the house of a widow, whose husband was one of
the governor’s head men. She is the only wife that bore children to
the deceased, and in consequence was not taken and sold at her
husband’s death. She wears a rope round her head, another round
her neck, and one round her waist, until she has passed her time of
mourning, or procures another husband; but I suspect this will be
until she dies, as she is ugly in the extreme. I had a visit, amongst
the number, from the daughter of an Arab, who is very fair, calls
herself a white woman, is rich, a widow, and wants a white husband.
She is said to be the richest person in Wawa, having the best house
in the town, and a thousand slaves. She showed a great regard for
my servant Richard, who is younger and better looking than I am: but
she had passed her twentieth year, was fat, and a perfect Turkish
beauty, just like a walking water-butt. All her arts were unavailing on
Richard: she could not induce him to visit her at her house, though
he had my permission.
The next day I went, after sending to say I was ready to give the
governor his present, to his house, accompanied by his head man,
and gave him seven yards of red cloth, seven yards of blue cloth,
seven yards of blue silk, an umbrella, ten strings of beads, and a
phosphorus box, after showing them off to the greatest advantage, a
thing never to be neglected in Africa. I sat down and told him what I
have told them all, and which has been so often repeated. He said
there were two roads, one where there was war, the other peace.
The one where there was war was by Youri; that the sultan of that
country was out fighting the Fellatas: the other by the way the
merchants went, through Nyffé, which was safe, and he would
advise me to go by that road. I thanked him, and said I would follow
his advice, for that I had nothing to do with war. Says he, “You are
come to make peace among all people, and make the kings leave off
war.” I said, “God willing, I would do what I could.” This opinion of my
being a peace-maker prevails strongly in all places that I have been
in: perhaps it may arise from the people of the coast and those of
Dahomey informing them of the active part we take in preventing the
slave trade. He said he should send to the sultan of Boussa, and tell
him to forward me by the way of Nyffé, with the merchants, as the
other road was bad; that he had never had such a valuable present
from any one before; and that I should see every thing I pleased in
his country. I told him that three white men who were with me had
died on the road; that I was very anxious to get to Bornou before the
rains, as being a dry sandy country, I considered that there I was
safe: but that in this country or Houssa it was very unsafe and
unhealthy for white men to be caught by the rains. The governor is a
thin, spare, old man; he had on a cap in the form of a foraging cap,
with some of the Stuart tartan riband in several folds around it, a
white tobe or large shirt, a Moorish kaftan of Manchester cotton, and
a pair of sandals on his feet. The room in which he received me had
nothing worth note but the stool on which he sat, which had two
lizards carved in bas relief on the top, and the heads of two as
handles for carrying it. His house is inside a high square clay wall,
with one gate on the western side, and consists of coozies, or
circular huts, built of clay and thatched, and one square tower of
clay, having little projections at each corner, and an ostrich egg on
the top of each of the huts.
After returning home I had numerous visitors, who brought
presents of rum, palm wine, and pitto, none of which I would accept,
nor allow to be brought into the house for the servants; but as for my
man Ali, an Arab, whose freedom I had purchased at Badagry and
taken as a servant, all my care could not prevent him from getting
drunk. He is a confirmed liar and a thief, and I have often regretted
that I gave him his freedom, as I cannot well get rid of him here. The
inhabitants of this place appear to be the most roaring, drinking set
of any other town I have yet seen. Last night, until near morning,
nothing was to be heard but fiddles, Arab guitars, castanets, and
singing.
The Kiama messenger, according to his promise, brought some of
the leaves of the tree or bush called by them kongkonie, from the
seeds of which the natives extract the poison for their arrows; from
the leaves and branches exudes a resinous gum which sticks to the
fingers; the flower is small and white, with a very long foot-stalk; the
seeds are enclosed in a long case surrounded by a silky substance;
the seeds are small, like caraway seeds, and are boiled to a thick
black paste before they are put on the arrows. They say that the
seeds are a deadly poison if taken into the stomach; the seeds I
have got in the case, but dried, and fit for use.
The king of Dahomey’s messengers came to me in the evening
and told me they wanted to speak to me, saying they wished to do
so privately. I sent Pascoe to one side with them, but they came
back observing that they must say it to myself only; their mighty
secret was this: that they had been in Youri five months assisting the
king of that country against the Fellatas; that, if I either regarded my
safety or wished to reach the end of my journey, I ought not to take
that road, as I should never get on; that they had stood the brunt of
all his battles, and that all their guns but two were burst; that they
were now on their way to their own country, but expect to be sent
back by the king of Dahomey with a larger force after the rains. They
said that Niki was the capital of Borgoo and not Kiama; that it is
fifteen days only from Dahomey; that Borgoo and Dahomey are
joined together, or two neighbouring kingdoms; that there are high
hills on the road between Niki and Dahomey; that they left the Maha
country on their left hand when they came here; that Kiama is five
days distant from Niki; that it is from Dahomey the people of these
countries receive all their rum and European articles. This account I
believe to be true, as I have seen great abundance of rum, pewter,
and earthen ware. They begged I would send a letter by them to say
I had met them, which I shall do to-morrow. They are much superior
looking men to the people of Wawa, and from their knowledge of
white men in their own country, have been very civil to me. They
seem to entertain a poor opinion of the courage and behaviour of the
people of Youri and of this country, and say that with a few men they
could take them all.
Thursday, 23d.—I had heard various stories, at different places on
the road, concerning the fate of the late unfortunate and enterprising
travellers Park and Martin, none of which I considered worth relating
except that which I now heard from the governor’s head man; but
they all with whom I have conversed agree in asking me if I am not
going to take up the vessel, which they say still remains. The head
man’s story is this: that the boat stuck fast between two rocks; that
the people in it laid out four anchors a-head; that the water falls
down with great rapidity from the rocks, and that the white men, in
attempting to get on shore, were drowned; that crowds of people
went to look at them, but the white men did not shoot at them as I
had heard; that the natives were too much frightened either to shoot
at them or to assist them; that there were found a great many things
in the boat, books and riches, which the sultan of Boussa has got;
that beef cut in slices and salted was in great plenty in the boat; that
the people of Boussa who had eaten of it all died, because it was
human flesh, and that they knew we white men eat human flesh. I
was indebted to the messenger of Yarro for a defence, who told the
narrator that I was much more nice in my eating than his countrymen
were. But it was with some difficulty I could persuade him that if his
story was true, it was the people’s own fears that had killed them;
that the meat was good beef or mutton; that I had eaten more goats’
flesh since I had been in this country than ever I had done in my life;
that in England we eat nothing but fowls, beef, and mutton.
 The women here are marked on the body somewhat in the
manner of the lace on a hussar’s jacket: in some, where the skin has
not healed properly, it looks very disgusting.
The widow Zuma has been kind enough to send me provisions
ready cooked, in great abundance, ever since I have been here.
Now that she has failed with Richard, she has offered Pascoe a
handsome female slave for a wife, if he could manage to bring about
matters with me. Not being much afraid of myself, and wishing to see
the interior arrangement of her house, I went and visited her. I found
her house large, and full of male and female slaves; the males lying
about the outer huts, the females more in the interior. In the centre of
the huts was a square one of large dimensions surrounded by a
verandah, with screens of matting all around except in one place,
where there was hung a tanned bullock’s hide; to this spot I was led
up, and, on its being drawn on one side, I saw the lady sitting cross-
legged on a small Turkey carpet, like one of our hearth rugs, a large
leather cushion under her left knee; her goora pot, which was a large
old-fashioned English pewter mug, by her side, and a calibash of
water to wash her mouth out, as she alternately kept eating goora
and chewing tobacco-snuff, the custom with all ranks, male or
female, who can procure them: on her right side lay a whip. At a little
distance, squatted on the ground, sat a dwarfish hump-backed
female slave, with a wide mouth but good eyes: she had on no
clothing, if I except a profusion of strings of beads and coral round
her neck and waist. This personage served the purpose of a bell in
our country, and what, I suppose, would in old times have been
called a page. The lady herself was dressed in a white coarse muslin
turban; her neck profusely decorated with necklaces of coral and
gold chains, amongst which was one of rubies and gold beads; her
eyebrows and eyelashes blacked, her hair dyed with indigo, and her
hands and feet with henna; around her body she had a fine striped
silk and cotton country cloth, which came as high as her tremendous
breasts, and reached as low as her ankles; in her right hand she
held a fan made of stained grass, of a square form. She desired me
to sit down on the carpet beside her, which I did, and she began
fanning me, and sent hump-back to bring out her finery for me to
look at; which consisted of four gold bracelets, two large paper
dressing-cases with looking-glasses, and several strings of coral,
silver rings, and bracelets, with a number of other trifling articles.
After a number of compliments, and giving me an account of all her
wealth, I was led through one apartment into another, cool, clean,
and ornamented with pewter dishes and bright brass pans. She now
told me her husband had been dead these ten years, that she had
only one son, and he was darker than herself; that she loved white
men, and would go to Boussa with me; that she would send for a
malem, or man of learning, and read the fatha with me. I thought this
was carrying the joke a little too far, and began to look very serious,
on which she sent for the looking-glass, and looking at herself, then
offering it me, said, to be sure she was rather older than me, but very
little, and what of that? This was too much, and I made my retreat as
soon as I could, determined never to come to such close quarters
with her again. During the night squally, with thunder, lightning, and
rain.
Friday, 24th.—Amongst my numerous visitors this morning, I had
a travelling musician, attended by two boys. His instrument was a
violin made of a gourd, with three strings of horse hair, not in single
hairs, but a number for each string untwisted; the bow the same; the
body of the violin was formed of half a long gourd; the bridge, two
cross sticks; the top, the skin of a guana stretched tightly over the
edges; the neck was about two feet long, ornamented with plates of
brass, having a hollow brass knob at the end. To this instrument was
hung a diminutive pair of sandals to denote his wandering
occupation, a piece of natron, strings of cowries, and stripes of cloth.
He said he would take any thing that was given to him. The boys had
hollow gourds with stones or beans in them, with which they kept
time by holding them in one hand and beating them against the
other. The musician himself was past the middle age, his beard
being tinged with gray, and neither too long nor too short; his face
inclining more to long than oval, with a nose slightly hooked; his
forehead high; his eyes large, bright, and clear, with a kind of
indefinable expression of half rogue and half a merry fellow, and
when he sang he sometimes looked sublime; his mouth and teeth
were good; his voice clear and melodious; his stature about the
middle size, and spare form; his dress was a white turban and large
sky-blue tobe or shirt. He accompanied his instrument with his voice,
the boys joining in chorus. His songs were extempore. I should have
taken one down, but found they were all about myself; and a number
of visitors coming in, I gave him fifty cowries and sent him away
rejoicing. Received a present of a sheep, yams, milk, eggs, and a
goat, from the governor.
I went outside the town with Yarro’s messenger to see the
kongkonie tree which I have before mentioned, and from the seeds
of which they are said to extract the poison for their arrows. The tree
is a parasite (meaning probably a creeper), about the thickness of a
man’s thigh at the root, from which shoot up several stems, that
ascend the large tree at the root of which it grows, twisting itself
round the stem and branches to the top of the tree; the bark of the
young branches is like the darkest of the hazel; the stem and older
branches smooth and whitish, like the bark of the ash; the flower,
which is now fading, has five leaves tapering to a point, from which
they have a string about two inches in length hanging; they are about
the size of our primrose, but of a darker yellow; the leaves of the tree
are rough and furry, exuding a gum that sticks to the fingers; the part
which grows from the flower and contains the seeds is about a foot
and a half in length, and one and a half or two inches in
circumference in the thickest part; the seeds are like caraway seeds,
and are surrounded by a silky substance; they are boiled until they
turn into a paste, when they are fit for use, and put on the arrows. I
had a present of five alligators’ eggs sent me by the governor; they
are only eaten by the principal people, and considered a great
delicacy: they were brought from the banks of the Quorra. The taja
called upon me, but he appeared still to shuffle off coming to any
arrangement, saying he could not say for how much he would carry
me to Kano, until he saw whether I was to go with him or not. I
observed to him it was very easily said, and that until he told me how
much, I would not ask the governor to go with him. He said he
wanted half the money here. To which I replied, “You must go with
this understanding in all future affairs between you and I, that I will
not give you one farthing until I arrive in Kano, when, the day after I
arrive there, you shall have every cowrie of the money. If you come
to any bargain with me, it must be with the understanding that I have
no money here.” “Well,” says he, “I will call to-morrow and see your
things, and then come to a written agreement with you—half the
money here.” This taja must take me for a fool; I will sooner stay
here all the rains, than let him have the money and leave me in the
lurch.
Saturday, 25th.—Clear and warm. At noon the taja visited me,
when, after a great deal of unnecessary palavering and manœuvring
on his part, we came to the following bargain,—that he is to carry all
my baggage and stores to Kano for 200,000 cowries. I also found
out that he does not go to Boussa, but crosses the Quorra at a place
called Comie, and goes to Koolfu in Nyffé, where he stops for a few
days. I am therefore to ask the governor here to carry my baggage to
Koolfu, where the taja will find bullocks. I must however go out of the
way to visit the sultan of Boussa, as all this part of the country is
nominally under him. The sultan of Niki is next to him, and equal to
him in power. My baggage, therefore, and stores with my servants
must proceed to Koolfu without me, as I have no other alternative but
to take this route or that of Youri. After the taja left me, I went to the
governor, and acquainted him with the agreement I had come to with
the taja, who immediately promised to send a messenger with myself
to Boussa, and another with my servants and baggage to see them
safe to Koolfu. I would not on any account miss the opportunity of
going to Boussa, being most anxious to see the spot where Park and
Martin died, and perhaps get their papers. If I am detained, my
servants go on with the taja; and I have left directions with them how
to proceed in the event of my death or other accidents.
Sunday, 26th.—On inquiring to-day of the same person, the
governor’s head man, concerning the fate of Park and Martin, he
said the natives did shoot arrows at them, but not until guns had
been fired from the boat: in all other parts of the story he agreed with
what he had told before, adding, that the boat was to be seen above
water every Sunday. They all treat the affair with a great deal of
seriousness, and look on the place where the boat was wrecked with
awe and superstition, telling some most marvellous stories about her
and her ill-fated crew. I also learnt from this man their manner of
burial in Borgoo, which is as follows: they dig a deep round hole like
a well; the corpse is put in the hole in a sitting posture, with the
wrists bound tight round the neck, the legs bent, and the thighs, legs,
and arms, bound tight round the body. The grave is made in the floor
of the deceased’s house, and his horse and dog, if he has any, are
killed to serve him in the next world. The Mahometans bury in their
usual fashion, and have a burying-ground on the east side of the
town, inside the walls.
Monday, 27th.—Received a present of a goat, two fowls, yams,
and milk, from the brother of the governor, who has got a sore leg,
and wishes me to cure it. In the afternoon we had thunder, lightning,
and rain. I took this opportunity of waiting on the governor to press
my departure, as the taja is rather too slack for me. I asked him if he
would not send me to Koolfu to-morrow, as he saw now that the
rains were close at hand. “Oh,” says he, “they will not set in these
two months, yet it is always thus before the rains.” I told him that no
one knew the seasons better than I did; and that, if I travelled as
slow as I had done of late, I would be caught by the rains in Houssa,
and I might as well have a sword run into my breast. He said he
would send for the taja to-night, and give me into his charge. I said, I
must go to Boussa, and make a present to the sultan; that if I did not,
he would say, a white man has passed through my country without
paying his respects to me, or bringing a present: it would be going
out of the country like a thief, not like the messenger of the king of
England. “Very well,” says he, “I will despatch a messenger with you
to request he will not detain you. You must send all your things up to
my house; I will give them and your servants in charge of the taja,
and all will go well; my messenger shall accompany them to
Koolfu”—(sometimes pronounced Koolfie and Koolfa). He then
began asking me if Englishmen would come into the country. “Yes,”
says I, “if you use them as well as you have done me: there is now a
doctor on his way to join me from Dahomey.” He said he would be
very glad to see him, and would forward him on to me. I asked him if
this country or Borgoo owed any allegiance to Yourriba: he said,
none; and laughed at the idea. He said he owed allegiance to
Boussa, as Kiama, Niki, and Youri did; that he was separated from
Kiama by the brook I halted at the second day I left that place, and
that the province of Wawa extended as far south as Rakah; that
Kiama owed no allegiance to Yourriba, but was a province of Borgoo,
subject to the sultan of Borgoo, who was the head of all: he added,
the sultan of Boussa could take Yourriba whenever he chose, but,
says he, the Fellatas will take it now. I asked him if he thought the
sultan of Boussa would give me the books that were found in the
boat belonging to the white men lost there. He said, if there were
any, he would certainly give them to me, as they were of no use to
him, he could not read; and he then related to me the same story
nearly that his head man had told me of that affair, and asked me if
the unfortunate people were not my countrymen, and had great
riches: I said they were, but that they were not rich, but honest men
like myself; that one, the head man, was a doctor.
Tuesday, 28th.—This morning I visited the governor’s brother who
has got the sore leg, as he had sent a fee, and could not come and
see me. His left ankle was dreadfully ulcerated and swelled, and had
been in the same state since the last rainy season. The leg was thin
and wasted; and he complained of suffering much pain. He could
move his toes very well; and inquiring if it was the effect of a hurt, he
said no, that it had come on at the beginning of the last rains. I
directed him to wash it clean night and morning with warm milk and
water, to apply poultices night and day until the swelling was
reduced, and on no account to drink spirits or palm wine: an advice
which he did not at all admire, as he said when he drank it eased his
pain and gave him sleep. I desired moreover that when the swelling
in his leg was reduced by the poultices, he should put clean fat on a
soft rag and lay over it, and on no account to drink any thing stronger
than water. After my return home he sent me a present of a sheep,
four fowls, eggs, milk, and honey. I now began to prepare for starting
to Boussa in the morning at daybreak, but the taja is working against
me, and I doubt being able to get off, as I have just learned that he
does not leave this until Saturday next, and wishes to detain me
also. The sky being clear, before the moon rose I was able to get the
meridian altitude of the star Dubbe in the Great Bear, which gave the
latitude of my house in Wawa, 9° 53′ 54″ north. Its longitude I
calculate to be 5° 56′ east.
 Wednesday, 29th.—Wawa is the capital of a province of the same
name in the kingdom of Borgoo; it is in the form of a square, and
may contain from eighteen to twenty thousand inhabitants. It is
surrounded by a good high clay wall and dry ditch; and is one of the
neatest, most compact, and best walled towns between this and
Badagry. The streets are wide, spacious, and airy, the houses of the
coozie, or circular hut form; the huts of each house being connected
by a wall, forms an airy and open space inside, and does not take
away from the regular appearance of the houses. One of the coozies
next the street has two doors, which forms an entrance into the
interior, into which the other coozies open. The plan of the one in
which I lived may serve for all, except the governor’s and that of the
widow Zuma. This plan will afford a fair specimen of the
accommodations of Wawa. The governor’s house is surrounded by a
clay wall, about thirty feet high, in the form of a square, having large
coozies, shady trees, and square clay towers inside.

A. Sleeping and sitting-rooms. c. Little houses for holding grain. F. House of entrance.
B. Stables. D. Houses of the slaves. 4. Places for cooking.

The marriages of the Wawanies are very simple. The pagans

make up matters with the girl first, give the father or mother a
present, and all is right. The Mahometans read the fatha, and make
a present; read it again, and part, when tired of one another. The
virtue of chastity I do not believe to exist in Wawa. Even the widow
Zuma lets out her female slaves for hire, like the rest of the people of
the town. Neither is sobriety held as a virtue. I never was in a place
in my life where drunkenness was so general. Governor, priest, and
layman, and even some of the ladies, drink to excess. I was
pestered for three or four days by the governor’s daughter, who used
to come several times in a day, painted and bedizened in the highest
style of Wawa fashion, but always half tipsy; I could only get rid of
her by telling her that I prayed and looked at the stars all night, never
drank any thing stronger than roa-in-zafir, which they call my tea,—
literally hot water: she always departed in a flood of tears.
Notwithstanding their want of chastity, and drunkenness, they are a
merry people, and have behaved well to me. They appear to have
plenty of the necessaries of life, and a great many of the luxuries,
some of which they would be better without; this being the direct
road from Bornou, Houssa, and Nyffé, to Gonja, Dahomey, and
Jannah. Since the war between the Fellatas and people of Yourriba,
they are able to procure plenty of European articles, such as pewter
jugs and dishes, copper pans, earthenware, Manchester cottons, &c.
Their fruits are limes, plantains, bananas, and several wild fruits in
the season. Their vegetables are yams, calalou, or the leaves of a
plant which they use in their soups, as we do greens or cabbage;
grain, doura, Indian corn, and millet. Fish they procure in great plenty
from the Quorra and its tributary streams: those I have seen were all
smoked, and principally a kind of catfish. Their best and largest
horses come from Bornou: the native breed are small, like the
Shetland ponies, hardy, active, and generally of a brown or mouse
colour. Oxen are in great plenty, principally in the hands of the
Fellatas; sheep and goats are also plentiful; domestic fowls plenty
and cheap; honey and bees’ wax abundant; ivory and ostrich
feathers they say are to be procured in great plenty, but they can get
no sale for them. The country abounds in wild animals of all the
different kinds to be found in Africa. Slaves are numerous: the males
are employed in weaving, collecting wood or grass, or on any other
kind of work; some of the women are engaged in spinning cotton
with the distaff and spindle, some in preparing the yarn for the loom,
others in pounding and grinding corn, some cooking and preparing
cakes, sweetmeats, natron, yams, and accassons, and others selling
these articles at the markets; the older female slaves are principally
the spinners. The mere labour is very light, and a smart English
servant would accomplish their hardest day’s work in one hour: but if
their labour be light their food is also light, being confined to two
meals a day, which almost invariably consist of paste of the flour of
yams, or millet, in the morning about nine o’clock, and a thicker kind,
approaching to pudding, after sunset, and this only in small
quantities; flesh, fowl, or fish, they may occasionally get, but only by
a very rare chance. Their owners, in fact, fare very little better:
perhaps a little smoke-dried fish, or some meat now and then;
principally only a little palm oil, or vegetable butter, in addition to their
paste or pudding; but they indulge freely in drinking palm wine, rum,
and bouza.
Of the slaves for sale I can say but little, and a stranger sees very
little of them. In fact when not going on a journey to some slave mart,
or sent out to the wells or rivers in the mornings to wash, they are
seldom seen. Even then they are fastened neck to neck with leather
thongs; and when this duty is over, they are confined closely in the
houses until they are marched off. When on their march, they are
fastened night and day by the neck with leather thongs or a chain,
and in general carry loads; the refractory are put in irons, in addition
to the other fastening, during the night. They are much afraid of
being sold to the sea coast, as it is the universal belief that all those
who are sold to the whites are eaten; retorting back on us the
accusation of cannibalism, of which they have perhaps the greatest
right to blame us. The slaves sold to the sea coast are generally
those taken in war, or refractory and intractable domestic slaves.
Nyffé at present is the place that produces the most slaves, owing to
the civil war raging in that country.
The people of Wawa would take beads in exchange for any
articles their country might produce; also brass bracelets for the
arms and legs; brass, copper, pewter, and earthenware dishes;
Manchester cottons of gaudy colours, and calicoes. Their arms are
bows and poisoned arrows, and light spears. They say they do not
like war, but appear to be very tenacious in not permitting
interference with their country; and they like the Fellatas better than
their neighbours of Kiama, of whom they are very jealous. They have
a good character for honesty; are cheerful, good-natured, and
hospitable; and no people in Africa that I have met with are so ready
to give information about the country as they are; and, what is very
extraordinary, I have not seen a common beggar amongst them.
They deny their Borgoo origin, and say they are descended from the
people of Nyffé and Houssa. Their language is a dialect of the
Yourriba: but the Wawa women are very good-looking, and the
Youriba women are not: the men are strong and well made, but have
a debauched look. Their religion is partly a loose Mahometanism,
and partly pagan. The most pious of the former can only say a few
prayers, or go through the necessary forms, and are called Malem,
or learned: the latter are called Kaffirs; and what they worship it is
hard to tell; every man choosing his own god, which they pray to that
he may intercede with the Supreme Being for them; and they offer
sheep, dogs, and sometimes a bullock, according to the benefit they
expect. A woman is sent to the market and sold, if, when she has a
child at the breast, she is known to go with a man, and, in addition,
loses her child, and is flogged.
In this country, as well as in all others I have passed between this
and the sea, I have met with tribes of Fellatas, some of whom are
not Mahometans, but pagans. They certainly are the same people,
as they speak the same language, have the same features and
colour, except those who have crossed with the negro. They are as
fair as the lower class of Portugueze or Spaniards, lead a pastoral
life, shifting from place to place, as they find grass for their horned
cattle, and live in temporary huts of reeds or long grass.
Thursday, 30th.—Having had every thing prepared last night for
starting this morning at day-break, I went and took leave of the
governor, who repeated his promises of sending my baggage on to
Koolfu. On my return from the governor, I met a messenger of the
sultan of Boussa, who had been sent expressly for me. He said he
would just wait on the governor, and deliver a message, and follow
me. I left Wawa, mounted on an old red roan mare of the governor’s,
on a good road, leading through a woody country, with numerous
plantations of yams, and Indian corn. At 8.30 A.M. passed a village
about a quarter of a mile from the south side of a range of low rocky
hills, running in a direction from east-south-east to west-south-west
by compass. The rocks were composed of pudding-stone, the white
quartz pebbles of which were square, not rounded, and imbedded in
a gray substance. At the end of an opening in the range was a
beautiful sugar-loaf mountain, overlooking all the rest, and bearing
from the village east-south-east, distance half a mile. This I
presumed to call Mount George, after his present majesty George
the Fourth. After passing the village and entering amongst the hills, I
found the valleys well cultivated, and planted with yams, corn, and
maize, but the road winding and rocky. At 10 A.M. came to the
village of Injum, the first belonging to the province of Boussa. Here I
halted, until the messenger, who had joined me some time before,
got his breakfast. This village is on the north-east side of the hills.
Amongst the number of people who came to look at me was a
woman, whose face, neck, right breast, and part of her right arm,
were covered with a scurf, like a person very ill with the small pox:
the borders of the scurf were bare, raw, and inflamed. This is the
disorder the young man’s mother died of, to whom I gave the
medicines at Kiama. When the disease reaches the toes and fingers,
they first contract, and then drop off; when, in a short time after, the
unfortunate person is relieved by death, as they have no cure for it,
nor do they attempt any. I called the woman, and asked her if she
suffered much pain: she said no, nor did it itch. She sent for some
yams, and offered them, as she said my looking at her would do her
good.
At 10.30 the messenger having finished his breakfast, we left
Injum. He gave me his horse to ride, as I could not get the old Wawa
mare to go on without a great deal of beating. At noon halted at the
side of a brook, to water the horses. Here end the hills and the
pudding-stone of which they are composed, and the rocks are now a
dark gray slate, which moulders away with the rains, the soil a strong
blue clay, with deep gullies formed by the rains. At 1 left the brook:
the country thickly wooded with tall trees, amongst which are a
number of the acacia or mimosa, many of them thrown down by the
elephants, for the purpose of feeding on the upper and tender
branches. The traces of elephants, buffaloes, and the larger kind of
antelopes called in Bornou corigum, are numerous. At 2.40 halted at
a village of the Kumbrie, or Cambrie, a race of Kaffirs inhabiting the
woods, on both sides of the river. They made a great difficulty in
procuring me a drink of water, so I mounted and left them, and at
3.30 arrived at a branch of the Quorra, called the Menai, close to its
junction with a second branch. The Menai is about twenty yards in
breadth, and about two fathoms in depth; the current hardly
perceptible, and the water dark and muddy; that of the branch into
which it runs being about thirty yards in breadth, with a strong
current, about three or four knots, throwing a back-water up the
Menai. The island on the other side of it is low and swampy, and
covered with high reeds; the colour of both the streams red and
muddy, as if in flood; but the messenger, on my asking if this was the
case, said no, that the river was now at its lowest mark, and pointing
to a place on the opposite bank of the Menai, about fifteen feet
above the present level, said the river rose to that height during the
rains. The trees on both banks were close down to the water’s edge,
and the branches were in the stream, and every now and then a
branch would be broken off, and washed away by the strength of the
current. From this, and the muddiness of the water, I concluded it
was rising; but certainly the inhabitants must know best: had I not
made inquiry, I should certainly have said it was rising. The canoe
being on the other side of the Menai, the messenger stripped off his
tobe, and swam over for it. After crossing and swimming the horses
over, in about a quarter of an hour’s ride I entered the walls of
Boussa, by the western gate. The walls appeared very extensive,
and are at present under repair. Bands of male and female slaves,
accompanied by drums and flutes, and singing in chorus, were
passing to and from the river with water, to mix the clay they were
building with. Each great man has his part of the wall to build, like
the Jews when they built the walls of Jerusalem, every one opposite
his own house.
I was much surprised, after entering the gate, to see only clusters
of huts here and there, and no regular town, as I had been led to
expect. I remained under the shade of a tree until the messenger
went and acquainted the sultan of my arrival. On his return I
accompanied him up to the sultan, whom I found sitting under a
small projection of the verandah of one of his coozies: his midaki, or
principal wife, sitting alongside of him. To this personage I had been
advised by the widow Zuma to pay particular attention, as she was
every thing with the sultan. He received me very kindly, and said the
sultan of Youri had kept seven boats waiting for me for these last