US3134649A - Nitrometer - Google Patents

Description

May 25, 1964 J. J. J. s'rAuNToN ETAL 3,134,649

NITROMETER Filed Jan. 3. 1961 ATTORNEYS.

United States Patent O 3,134,649 NITROMETER John I. J. Staunton, Gak Park, Lewis Malter, Niles, Edgar H. Stephens, Glenview, and Robert H. Smith, Jr.,

Wheaton, Ill., assiguors to Coleman Instruments, Inc., a

corporation of Delaware Filed Jan. 3, 1961, Ser. No. 80,272 8 Claims. (Cl. 231-253) This invention relates to a gas absorption apparatus adapted for use in a nitrometer, for measuring a volume of nitrogen in the analysis of nitrogen content by the Micro-Dumas method.

In analyzing for nitrogen content, a weighed sample is heated to combustion in an enclosed tube. The products of combustion are swept by a stream of carbon dioxide through heated nely divided copper and copper oxide beds which remove unwanted components. The remaining carbon dioxide and nitrogen are then conducted from the combustion train into a potassium hydroxide solution in a nitrometer. There they are passed as a stream of tine bubbles through the solution to remove the carbon dioxide, and the nitrogen gas accumulates at the top of the nitrometer where its volume subsequently may be determined.

The classical nitrometer, known as the Pregl nitrometer, consists of a caustic reservoir provided with a mercury seal in the bottom, and gas from the combustion train is introduced into the mercury and escapes into the caustic. A levelling bulb filled with caustic is connected to the caustic reservoir below the liquid surface level, and it serves to equalize the internal and external pressure during measurement of the volume of nitrogen collected in a graduated tube above the reservoir. A stop-cock valve closes the top of the graduated tube, and nitrogen is vented therethrough after measurement. This device is bulky and involves the handling of an awkward levelling bulb. Careful control of bubbley size and rate is required for the eective absorption of carbon dioxide, due to the poor dispersion of the entering bubbles. Bubbles of nitro gen tend to stick to the mercury-caustic interface and to creep up the side wall, and they must be dislodged to avoid error. Leakage occurs at the stop-cock. A substantial waiting period is required after combustion is complete, for complete carbon dioxide absorption, temperature equalization, and drainage of caustic from the walls of the graduated tube. These effects vary considerably with changes in manipulation of the levelling bulb and operating technique.

A new form of nitrometer which eliminated some of the defects was devised recently, as described in Microchemical Journal, vol. IV, pages 43-54, 1960. A shorter, larger diameter caustic reservoir is provided with a side gas inlet into the caustic, with the elimination of the mercury seal. Instead, the gas inlet is provided with a Bunsen valve, formed by a slit in the side of a terminal rubber tube with a closed end. A magnet encased in Teiion is provided in the caustic reservoir, and it is operated as a magnetic stirrer, resting on the bottom of the reservoir beneath the Bunsen valve. A fixed side arm pressure equalizing vessel is connected to the reservoir and cornmunicates therewith below the liquid level. The gas collected above the reservoir is measured by a calibrated piston and cylinder or syringe, which is operated to bring the caustic level in the reservoir back to a reference level after gas is introduced. The caustic in the reservoir is then level with the caustic in the pressure equalizing vessel. Connection of the gas absorption apparatus to the piston and cylinder measuring apparatus and to the combustion train is made through ground and waxed ball and socket type joints.

The foregoing design eliminates the bulk and awkwardness of the Pregl nitrometer, but it also suiiers from several disadvantages. The effectiveness of the stirrer is borderline, because it is too remote from the bubble stream. The Bunsen valve is hard to make and maintain, and tends to introduce error-producing contamination. The design is prone to leakage at the piston seal, at the joints, and at the Bunsen valve. If the latter leaks, a pressure drop in the combusiton train might cause caustic to be drawn back through the system with disastrous results. The joints are hard to make and break.

The present invention has for its object to provide a new and improved nitrometer and a gas absorption apparatus adapted for use therein, and in other applications, which overcome these and other prior disadvantages, and which are especially characterized by accuracy of measurement, and ease and rapidity of operation.

Arr important object is to provide better breakup and dispersion of gas bubbles from the combustion train in the absorption apparatus and to prevent them from sticking in the apparatus, while increasing the time in the absorption medium.

Another object is to provide an absorption appartus which includes a mercury seal, in which the gas bubbles are prevented from adhering to the mercury-caustic interface.

An additional object is to provide central release of the gas into the aborption medium, together with uniform non-turbulent rotational stirring of the medium and upward central 'helical travel of the gas bubbles.

A further object is to provide an apparatus which is not prone to leakage in operation, and which may be disconnected from the system easily and rapidly when operation is discontinued or at any other time.

These and other objects, advantages and functions of the invention will be apparent from the specification and from the attached drawings illustrating preferred embodiments of the invention, in which like parts are identified by like reference symbols in each of the views, and in which:

FIGURE 1 is a vertical sectional and elevational view of one embodiment of the new nitrometer;

FlGURE 2 is a fragmentary vertical sectional view of a modification of the gas absorption apparatus illustrated in FIGURE l; and

FIGURE 3 is a fragmentary vertical sectional view of another modified form of the gas absorption apparatus.

The present invention provides a number of improve` ments over the aforementioned nitrometer described in the Microchemical Journal. The gas absorption apparatus is especially characterized by provision of an absorption chamber adapted to serve as a caustic reservoir, a mercury chamber therebelow, a restricted passageway between the chambers, and means for releasing a stream of gas in the mercury chamber beneath the passageway. Stirring means preferably are provided in the absorption chamber above the passageway. The new construction is very effective in breaking up and dispersing gas bubbles, preventing bubble adherence, and producing rapid complete absorption of carbon dioxide and accumulation of the nitrogen gas. The construction provides a number of additional signicant advantages, as will appear from the description which follows.

Referring to the drawings, a nitrometer 10 is illustrated in FIGURE l, and it includesa gas absorption apparatus generally indicated by the numeral 12 and measuring apparatus generally indicated by the numeral 14. The absorption apparatus is connected by a conduit 16 to the combustion train, not shown, wherein a sample is combusted and the products are removed by a stream of carbon dioxide according to the Micro-Dumas method.

The absorption apparatus 12 includes a cylindrical absorption chamber 18 having a ground llat bottom 20, a circular vertical side wall 22, and an upwardly and inwardly inclined conical top wall 24. A central or axial integral tubular neck 26 is provided on the top wall 24 of the absorption chamber. It has a relatively narrow cylindrical bore 28 in its lower portion, and an enlarged upper cylindrical bore 30 commencing at a point 32 spaced above the chamber 18. The absorption chamber is lled with potassium hydroxide, normally to a reference mark 34 on the side of the neck 26, in the lower portion thereof.

A cylindrical mercury chamber or well 36 is arranged below the absorption chamber 18 in aligmnent therewith. The mercury chamber includes a flat bottom 38, a circular side wall 40, and an upwardly and inwardly inclined conical top wall 42. The mercury chamber communicates with the absorption chamber 18 at the bottom 20 thereof, and axially of the two chambers, through a restricted passageway or narrow tubular conduit 44 integral with the two chambers. Mercury is contained in the chamber 36, normally up to the bottom edge 46 of the restricted passageway.

A captive Teflon-covered cylindrical magnet stirrer 48 is contained in the absorption chamber 18, and it includes a central peripheral rib 50. The stirrer spins on the rib acting as a pivot, about the vertical axis of the restricted passageway 44. The stirrer spin is stabilized by the ground flat construction of the absorption chamber bottom 20, with no dragging at the ends of the stirrer or moving olf center. We have found that the magnet stirrer 48 can be driven from a driver magnet (not shown) rotated below the thickness of mercury contained in the well 36, taking advantages of the high resistivity of mercury with its resulting low eddy current attenuation of the driving eld.

A vertically arranged pressure equalizing vessel 52 is fixed on the gas absorption apparatus 12, by means of a connecting member 54 between the vessel and the absorption chamber 18. The vessel is open to the atmosphere or other source of known pressure at its upper end 56. It is filled with potassium hydroxide solution to a normal upper liquid surface level 58 in the same plane with the reference mark 34 on the absorption chamber neck 26. The pressure equalizing vessel is connected to and communicates with the absorption chamber by a tubular conduit 60. The conduit is connected to the lower end of the vessel, upwardly inclined from the vessel to the absorption chamber, and connected to the absorption chamber beneath the surface of the potassium hydroxide absorption medium when contained in the chamber.

A gas inlet tube 62 is fixed on the absorption apparatus by means of a connection 64 to the absorption chamber 18. The tube extends through the side wall 40 of the mercury well 36, to the central vertical axis thereof. The tube opens upwardly on the axis and beneath the restricted passageway 44, at a sharp edged horizontal delivery face 66. An arm portion 68 of the gas inlet tube is immersed 'n1 the mercury 70.

The absorption chamber neck 26 is connected to a conduit 72 in the measuring apparatus 14. The conduit provides an air buer between the caustic and the piston and cylinder, described below. This connection and a connection of the gas inlet tube 62 to the combustion train conduit 16 are made by sealed joints 74 and 76, respectively. Each joint includes a ball socket 78 having an upper peripheral flange 80, and a tubular male joint member 81 received therein which includes a clamping flange 82 and a resilient O-ring seal 84 at its lower end. The O-rings form reliably leak-proof joints with the ball sockets 78, and they are self-aligning and rapidly discon- 4 necting. The joints may be secured by conventional clamps 86 connected on the ange members 80 and 82 of the socket and male member.

The measuring apparatus includes a calibrated piston and cylinder or syringe 87. The cylinder consists of two tubular metal parts 88 and 89 each threaded at one end and there joined by a threaded coupling 90, and the cylinder is closed at the outer ends. A smooth surfaced metal piston or plunger 91 is mounted in the cylinder for reciprocal longitudinal movement. A seal ring 92 constructed of a resilient material such as neoprene or Teilon is clamped between the tubular parts, and it bears on the surface of the plunger between its ends. The seal partitions the cylinder to provide a gas chamber 93 in one part 88, which communicates through an opening 94 in the closed end of the part with the conduit 72 leading to the absorption chamber neck 26. The system is vented by means of a stop cock 104 in a branch line 105 connected to the conduit 72.

The piston 91. is driven by a micrometer screw 95 mounted in the cylinder head part 89. The screw is in threaded engagement with an adjustable micrometer nut 96 secured to the end of the piston. A guide pin 97 prevents the piston from turning. It is mounted on the side of the piston and moves together with the piston in a longitudinal slot 98 in the side wall of the head part 89. rThe micrometer screw shaft is supported by a sleeve 99 which extends through the end wall 100 of the head part 89. Collars 101 and 102 are secured on the sleeve adjacent to the opposite sides of the end wall, to prevent the screw from moving longitudinally. The screw is turned by an external digital dial 103, on which gas volume readings are made.

In operation with the apparatus of FIGURE 1, gas enters the combustion train through the submerged arm 68 of the gas inlet tube. Bubbles break olf cleanly at the sharp delivery face 66 of the arm, with no tendency of the bubbles to creep over and cling to side walls. The delivery tip is also clear and non-clogging.

The gas flow displaces the mercury in the gas inlet tube 62 and also some of the mercury in the well 36. This causes the mercury to rise in the restricted passageway 44, to the top of the passageway and on line with the bottom 20 of the absorption chamber at normal ilow rate. The emerging bubbles shrink almost at once in the circulating mass of absorption medium and are forthwith torn apart and further dispersed by the stirrer 48. The mercury level moves up and down in the passageway 44 as each bubble is expelled.

In this manner, the gas bubbles rise straight through an interface of small area between the mercury and the absorption medium, eliminating the tendency to stick at the interface and sweeping the interface clean. The pumping action of the mercury is a further safeguard against sticking of bubbles. With the bubbles broken up and dispersed as described above, rapid and complete gas absorption is achieved.

Should the ilow rate increase, the interface remains the same, because mercury is removed by stirrer action and driven to the bottom perimeter of the absorption chamber as indicated at 106 in FIGURE 3. At lower than normal gas evolution rates, the mercury level may be lowered in the restricted passageway 44. The pumping action of the mercury due to the bubble flow maintains a circulation of fresh potassium hydroxide in the passageway, so that carbon dioxide bubbles collapse immediately on leaving the interface and do not block the constriction.

A preferred exemplary construction of the restricted passageway 44 in the construction illustrated is about 4 millimeters long and has an internal diameter of about 4 millimeters. With a smaller diameter, there may be a tendency to trap and coalesce bubbles at low ow rates. With a larger diameter, the self clearing characteirstics of the small interface between the mercury and the potassium hydroxide may be vitiated.

Should a large gas evolution rate be experienced commonly during early stages of combustion followed by extended low rates thereafter, an increase in eliiciency and elimination of the requirement for manual return of excess mercury to the well after a run may be effected in the manner illustrated in FIGURE 3. A perimeter groove or sump 107 is provided around the bottom 20 of the absorption chamber, and it is connected to the mercury well 36 by a mercury return tube 108. With this construction, excess mercury will merely accumulate by centrifugal action as indicated at 106, and the mercurycaustic interface level -will be maintained near the top of the restricted passageway 44 for best absorption eiciency at both righ and low gas ow rates.

The stirrer 48 and its arrangement are especially important for producing rapid gas absorption at high rates of flow. It is supported by the absorption chamber bottom above the point of gas introduction, which provides greatly improved bubble breakup and dispersion. The stabilizing spin of the stirrer imparts a rotation to the absorption medium which causes the gas bubbles to follow a long upward helical path, shrinking as they go, as indicated by the lines 199 in FIGURE 3. The travel increases the available absorption time in the medium. The rotation of the medium also scrubs any clinging bubbles off the absorption chamber wall, causing them to move into the center of the medium adjacent the vertical axis of the absorption chamber by centrifugal vortex action.

The absorption chamber 18 is not encumbered by any drag-producing members, so that the rotation of the caustic absorption medium is not impeded or broken up into undesirable turbulence. At the same time, the arm 68 of the gas inlet tube 62 which is immersed in the mercury 70 prevents rotation thereof, to prevent wandering of the gas bubbles in the mercury well 36. The upward inclination of the conduit 60 from the pressure equalizing vessel `52 to the absorption chamber 18 precludes the trapping of gas bubbles in the conduit which was previously encountered. In the new construction, therefore, gas is delivered from below in the center of the apparatus with the elimination of factors tending to cause the bubbles to wander or be trapped by adhesion.

The enlarged bore 30 commencing at the point 32 in the absorption chamber neck 26 functions very effectively to break any bubbles which reach this point and prevent caustic from being swept up into the measuring apparatus 14. This construction requires no waiting period for temperature equalization before making a reading. When the nitrogen gas has accumulated over the caustic, the piston and cylinder 87 is operated by the digital dial 103 to move the piston 91 and bring the caustic level to the reference mark 34. The volume of nitrogen then is read on the dial. The new construction reduces the analytical time as much as ten to fifteen minutes below that required for the Pregl nitrometer. The increased speed coupled with increased accuracy and reduction of critical items of technique is of substantial importance in laboratory operations.

The mercury well 36 furnishes a protective seal against back flow into the combustion train. This safeguard is augmented by the high gas inlet tube 62 which extends upwardly in the apparatus and is secured to the absorption chamber 18. The delivery tip 66 on the gas inlet tube remains clear and open without the clogging tendencies of a valve device.

With any combustion train, a shut down for an extended period of time results in contraction of the gas in the system, which tends to draw the contents of the nitrometer back through the system. Likewise, in the event of a drop in temperature of the measuring apparatus 14, there may be a tendency to draw caustic absorption medium into this apparatus. The quick-disconnecting O-ring seal joints 74 and 76 enable the absorption apparatus to be removed at any time and avoid these possibilities. Also,

spent caustic is easily-replaced, since the absorption apparatus readily can be removed, and it is a free standing unit not subject to possible leakage.

The stirrer 48 may be captive, which has the advantage that it is protected from handling and is cleaned by the same chromic acid process used to clean the glass apparatus. This is important in preventing contamination of the stirrer surface by grease or other material which will cause adhesion of bubbles that are difficult to dislodge. The caustic absorption medium can be poured from the apparatus when spent, the apparatus can be rinsed repeatedly, and fresh medium can be added without losing a substantial amount of the mercury, which does not require replacement. The restricted passageway 44 serves to retain the mercury.

Should other considerations make it advisable for a non-captive stirrer to be used, the embodiment of FIG- URE 2 may be employed. The pressure equalizing vessel 52' thereof has an enlarged bottom opening 110 which enables the stirrer 48 to be removed therethrough. An enlarged conduit 60 is provided which includes a downwardly inclined bottom wall 111 merging with the bottom 20 of the absorption chamber. The wall inclination prevents mercury globules and associated gas bubbles from moving too far into the conduit, and the mercury will return to the absorption chamber 18. An upwardly inclined top wall 112 insures that gas bubbles which enter the conduit 60' will return to the absorption chamber. Also, the mercury reservoir can be lled through the pressure equalizing Vessel 52 if desired.

In the embodiment of FIGURE 3, the lower end of Y the conduit 60 leading from the pressure equalizing vessel to the absorption chamber is connected to the mercury well 36 by a mercury return leg or conduit 113. This leg serves to return any globules of mercury that may be swept into the caustic conduit 60. The stirrer 48 is then captive, as in the embodiment of FIGURE 1.

The invention thus provides a compact nitrometer gas absorption apparatus which 'functions Very rapidly and conveniently to perform accurate nitrogen analyses. The components of the apparatus combine to provide rapid and complete breakup and dispersion of gas bubbles without adhesion of the bubbles to various parts of the apparatus, wtih resulting rapid and complete gas absorption. The prior causes of inaccuracies, delays, leaks and backups have been obviated.

It will be apparent that various changes and modifications may be made in the preferred embodiments of the invention which are illustrated, and in the operation thereof, within the spirit and scope of the invention. It is intended that such changes and modications be included within the scope of the appended claims.

What we claim as new, and desire to secure by Letters Patent of the United States, is:

1. Gas absorption apparatus which comprises an absorption chamber, a mercury chamber therebelow, a restricted passageway of small cross section compared with the cross section of said chambers interconnecting said chambers for conducting gas to said absorption Ichamber, conduit means having an upwardly facing opening for releasing a stream of gas bubbles in said mercury chamber directly beneath said passageway, and stirring means in said absorption chamber directly above said passageway for breaking up gas bubbles entering said absorption chamber from said passageway.

2. Gas absorption apparatus which comprises an absorption chamber, a mercury chamber therebelow, a restricted passageway of small cross section compared with the cross section of said chambers interconnecting said chambers for conducting gas to said absorption chamber, conduit means having an upwardly facing opening for releasing a stream of gas bubbles in said mercury chamber directly beneath said passageway, stirring 'means in said absorption chamber directly above said passageway for breaking up gas bubbles entering said absorption chamber from said passageway, and a central tubular neck communicating with the top of said absorption chamber having a restricted bore therethrough to break up any bubbles which reach said neck and to hinder liquid flow therethrough.

3. Gas absorption apparatus which comprises an absorption chamber, a mercury chamber therebelow, a restricted passageway of small cross section compared with the cross section of said chambers interconnecting said chambers for conducting gas to said absorption chamber, conduit means having an upwardly facing opening for releasing a stream of gas bubbles in said mercury chamber directly beneath said passageway, stirring means in said absorption chamber directly above said passageway for breaking up gas bubbles entering said absorption chamber from said passageway, a pressure equalizing vessel xed on said apparatus, and 'conduit means connecting said vessel and said absorption chamber and being inclined upwardly from said vessel to said chamber.l

4. In a nitrometer, gas absorption apparatus which comprises an absorption chamber, a mercury chamber therebelow, a restricted passageway of small cross section compared with the cross section of said chambers interconnecting said chambers for conducting gas to said absorption chamber, conduit means having an upwardly facing opening for releasing a stream of gas bubbles in said mercury chamber directly beneath said passageway, magnetically actuated stirring means in said absorption chamber directly above said passageway for breaking up gas bubbles entering said absorption chamber from said passageway, a central tubular neck communicating with the top of said absorption chamber having a restricted bore therethrough, a pressure equalizing vessel xed on said apparatus, and conduit means connecting said vessel and said absorption chamber and being inclined upwardly from the vessel to the chamber.

5. The apparatus of claim 1 in which said mercury chamber is lilled with mercury at least to the lower end of the restricted passageway and said absorption chamber is filled with absorption medium to provide an interface of small area between the mercury and the absorption medium.

6. Gas absorption apparatus which comprises an absorption chamber, a mercury chamber therebelow, a restricted passageway of small cross section compared with the cross section of said chambers interconnecting said chambers for conducting gas to said absorption chamber, a conduit disposed within said mercury chamber and having an upwardly turned end with a sharp delivery face directly beneath said passageway for cleanly releasing a stream of gas bubbles, and stirring means in said absorption chamber directly above said passageway for breaking up gas bubbles entering said absorption chamber from said passageway.

7. Gas absorption apparatus which comprises an absorption chamber, a mercury chamber therebelow, a restricted passageway of small cross section compared with the cross section of said chambers interconnecting said chambers for conducting gas to said absorption chamber, conduit means having an upwardly facing opening for releasing a stream of gas bubbles in said mercury chamber directly beneath said passageway, said absorption chamber having a perimeter sump in the bottom thereof, an opening through the bottom of said sump to provide for draining mercury from the sump back to the mercury chamber, and stirring means in said absorption chamber directly above said passageway for breaking up gas bubbles entering said absorption chamber from said passageway.

8. The apparatus of claim 7 which includes a pressure equalizing vessel Xed on the apparatus, a conduit eX- tending downwardly from the bottom of said vessel to said mercury chamber, and a branch conduit extending upwardly from said downwardly extending conduit at a point above the top of the mercury chamber to interconnect said downwardly extending conduit to the absorption chamber.

References Cited in the iile of this patent UNITED STATES PATENTS 1,124,432 Heath Jan. 12, 1915 1,366,382 Heath Jan. 25, 1921 OTHER REFERENCES Gustin: Microchemical Journal, vol. IV, March 1960, pages 43-54.

Gustin: Microchemical Journal, v01. I, pages -87, 1957.

Claims (1)

1. GAS ABSORPTION APPARATUS WHICH COMPRISES AN ABSORPTION CHAMBER, A MERCURY CHAMBER THEREBELOW, A RESTRICTED PASSAGEWAY OF SMALL CROSS SECTION COMPARED WITH THE CROSS SECTION OF SAID CHAMBERS INTERCONNECTING SAID CHAMBERS FOR CONDUCTING GAS TO SAID ABSORPTION CHAMBER, CONDUIT MEANS HAVING AN UPWARDLY FACING OPENING FOR RELEASING A STREAM OF GAS BUBBLES IN SAID MERCURY CHAMBER DIRECTLY BENEATH SAID PASSAGEWAY, AND STIRRING MEANS IN SAID ABSORPTION CHAMBER DIRECTLY ABOVE SAID PASSAGEWAY FOR BREAKING UP GAS BUBBLES ENTERING SAID ABSORPTION CHAMBER FROM SAID PASSAGEWAY.

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