INDUSTRIAL AND ENGINEERING CHEMISTRY
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Vol. 15, No. 4
A New Specific-Gravity Apparatus for Natural Gas' By T.R. Weymouth, R. P.Anderson, and J. R. Fay UNITEDNATURALGAS Co., OILCITY, PA.
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HIS new apparatus varying specific gravities, A new apparatus has been described for determining the specific for determining the showed that the influence gravity of natural gas, which comprises an orifice and a Capillary specific gravity of of viscosity upon the differtube in the same gas line, with differential gages for each. The natural 'gas comprises an ential pressure is practimethod of operating and calibrating this apparatus has been disorifice and a capillary tube cally constant for these cussed and its field of usefulness compared with that of the wellin series, and the principle gases, and accordingly the known effusion apparatus. of its construction is based apparatus here described upon two facts, well known has been developed. to those familiar with the flow of fluids in pipe lines, which DESCRIPTION (IF APPARATUS may be stated as follows: (1)when a fluid is oassed throuah " a For convenience in field use, the apparatus has been built thin, sharp-edged orifice, the drop in preskre a t the orifice, known as the differential pressure, varies with the specific in compact, portable form, as shown in Fig. 1. The metal gravity of the fluid, other factors remaining constant; and case is 12 in. high by 8 in. wide by 6 in. deep, with a partition ( 2 ) when a fluid is passed through a small capillary tube at through the center from side to side. Back of the partition a low rate, the drop in pressure through the tube is a the orifice and capillary tube are suspended in water for confunction of the viscosity of the fluid, but is independent venient control of temperature, and in front of the partition of its specific gravity. It is thus obvious that, for fluids is a board to support the differential gages for the orifice of the same viscosity, the rate of flow of the fluid through and the capillary tube. Gas enters through tube A, which the orifice may be kept constant by maintaining a constant contains cotton for removing dust and other foreign matter differential pressure on the capillary tube, and that any from the gas, passes through fitting B, which contains an variation in the specific gravity of the fluid will result in a orifice 0.02 in. in diameter, then through a capillary tube, C, corresponding variation in the differential pressure at the and finally out of the apparatus a t D. The orifice is conorifice. In other words, the differential pressure a t the nected by copper tubing to differential gage E, read on inorifice is a measure of the specific gravity of the fluid and clined portion F, with scale G, calibrated in specific gravity. the differential gage scale-may be calibrated to read specific The inlet of the capillary tube is connected by copper tubing to differential gage H. This gage is inclined in the upper gravity directly, portion, J, to increase the accuracy of setting the fluid in the gage for the passage of gas a t a definite rate through the orifice. The capillary tube is of glass, has a bore of about 0.04 in., is about 28 in. long, and is cemented in the special fitting K with de Khotinsky cement. One-eighth inch standard brass pipe and fittings are used in the connections to the special fittings for the orifice and the capillary tube. The level L is attached to the board for convenience in setting the apparatus approximately horizontal before use. Xylol is used in both differential gages, which must be filled to the proper point before the apparatus is used.
MANIPULATION
FIG, I
The first application to be made of these facts has been in the determination of the specific gravity of natural gas. Preliminary experiments with a wet meter and small capillary tubes o n natural gases from western Pennsylvania, of widely 1 Presented before the Section of Gas and Fuel Chemistry a t the 64th Meeting of t h e American Chemical Society, Pittsburgh, Pa., September 4 t o 8 , 1922
The gas whose specific gravity is to be determined is passed into the apparatus through tube A a t a rate which mill produce a certain differential on the capillary tube J, and the specific gravity of the gas is read from the scale G. This specific gravity may be termed the observed specific gravity of the gas, and must be corrected to obtain the true specific gravity if the temperature of the gas passing through the apparatus differs from the calibration temperature, or if the barometric pressure differs froin the calibration pressure. The temperature of the water in the bath in which the orifice and capillary tube are suspended and the barometric pressure must be determined a t the time when the reading of the observed gravity is made; and b y the use of tables or charts the true specific gravity may easily be ascertained. CALIBRATION The apparatus in Fig, 1 was calibrated by using natural gases varying in specific gravity from 0.60 to 0.90, as deteimined by calculation from combustion data. Data have also been secured on the effect of variations in temperature and atmospheric pressure on the reading of the apparatus, and charts for the reduction of observed readings to true specific gravity have been prepared.
April, 1923
IND UXTRIAL AND ENGIhTEERING CHEMISTRY
FIELD OF USEFULNESS In the natural-gas industry there is need for an apparatus that will give accurate results in the field a t all times of the year. The effusion specific-gravity apparatus, now widely employed, gives trouble in cold 'weather, due to the difficulty of preventing the condensation of moisture in the orifice, and this difficulty is eliminated entirely with this new specific-
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gravity apparatus. Further advantages of the new apparatus as compared with the effusion instrument are the higher degree of accuracy and the shorter time required for a complete determination. Moreover, since the new instrument gives instantaneous readings, it responds readily to rapid changes in specific gravity, and can be adapted to recording purposes where gases of fluctuating gravities are flowing.
A New Method for the Control of Thermostats''z By D. J. and J. J. Beaver DEPARTMENT OF CHEMISTRY, COLUMBIA UNIVERSITY, NEW YORK. N. Y.
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Of A new method has been outlined for accurately controlling the the showingthat a dirty mercury surface has work On conductivity temperafure of a thermostat for long periods of time, which possesses less effect On the and viscosity measurethe following adoanfages: ( I ) the elimination of sparking at the when an Oscillating point is merits, it Was necessary to mercury contact, ( 2 ) an contact obtained without the used than when a fixed maintain a thermostat 'Onuse of elaborate mechanical equipment, ( 3 ) the elimination of the point is used. However, we to o.oolo for back-lash at the mercury contact, ( 4 ) the elimination of excessioe found after a day's run, months at a time* The wear on the relay points, and ( 5 ) a fhermoregulator which reacts when using the oscillating thermostats On the market w r y quickly to small changes in femperature. were found to be inadeWith this apparatus it is possible to maintain wafer or oil therpoint, the mercury surface quate for the purpose, mosfats of capacities oarying between 10 and 300 liters constant f o is so contaminated because Of Oxida0.001" C.over long periods of time with a minimum amount of with oxide that it has to be cleaned. tion of the mercury surface . in the thermoregulator. To prevent the formation This oxidation is caused of the oxide film on the merby the small electric arc produced when the contact is made cury, an atmosphere of hydrogen or nitrogen is maintained over or broken. This difficulty can be eliminated b y decreasing the surface. This method is satisfactory as long as the gas is the number of contacts per unit of time with a proportionate present, but is cumbersome because of the apparatus and care decrease in the accuracy of regulation or by making the required to maintain the supply of gas. Clark,e after filling current across these points so small that no arc can be pro- the space above the mercury surface with hydrogen, seals duced. The object, of the present paper is to describe a off the top of the thermoregulator so that no other gas can enregulating device which combines accuracy of regulation ter. With the thermoregulator sealed in this manner it is with constancy of regulation for long periods of time. difficult to adjust the temperature and impossible to use an Constancy of regulation by ,electrical methods depends oscillating contact,. King' claims to have secured satisfactory mainly on two interdependent devices-the thermoregulator results by replacing the air above the mercury with an inert gas and then sealing the capillary tube above the contact and the controlling mechanism. point with a drop of mercury. This method fails if the l)ISADV.4KTAGES O F OTHER THERMOREGULATORS regulator is jarred, because the drop of mercury gradually Many kinds of thermoregulators capable of indicating a works down to the main body of liquid and so changes the change of O.O0lo in the bath temperature have been described temperature of regulation. in the past. Nearly all of them are made of glass and contain A simpler and more permanent way to prevent this oxidaeither toluene and mercury or mercury only. The contact tion of the mercury is to use an electrical controlling mechais usually made between mercury in a capillary tube and a nism, which requires a very small current for its operation and fixed platinum point. It was observed by G o W that, if the which is so constructed as to be free from inductance or caplatinum point was made to oscillate UP and down for a dis- pacity. A properly constructed magnetic relay or solenoid tance of about 1 mm., more sensitive temperature control will operate satisfactorily with a current of 0.004 ampere was secured than when using the same thermoregulator with under a &volt drop of potential. However, even with this a fixed point. In recent articles by White4 and Sligh6 the small current an appreciable spark is formed a t the mercury advantages of the oscillating contact are discussed mainly surface, oxving to the large inductance of the relay coils. from the theoretical viewpoint. Sligh gives some data for A nonmagnetic controlling mechanism in which the expanshort runs on a thermostat, using first a fixed and then an sion of a brass tube, caused by the heating effect of the conoscillating contact point, which show that the latter gives a trolling current, is used to make or break the heater circuit, regu1at;on about fifty times as sensitive as the former-i. e., requires sufficient current to Cause considerable arcing a t the the temperature variation of the first was fifty times as great mercury surface. This arcing can be largely, but not cornas for the latter. It is stated that the mercury surface pletely, eliminated by the use of condenser of the proper ca"was in bad condition" but that this had very little effect on pacity across the contact points.
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1 Presented before the Division of Physical and Inorganic Chemistry a t the 64th Meeting of the American Chemical Society, Pittsburgh, Pa., September 4 to 8, 1922. 2 Contribution KO. 401 from t h e Department of Chemistry, Columbia University, New York, N. Y. 8 J. rhzm. bhys., 6 (1S97),479. 4 P h y s . Reu., 16 (1920), 509, J. Wash. Acad. Sci., 10 (1920),429 J. A m . Chem. Soc., 44 (1922). 60.
METHODOF REGULATION After trying several different methods we found that the most satisfactory way to Overcome these drawbacks is to use a very small current across the mercury contact and then 6
J. A m . Chem. Soc., 25 (1913). 1889.
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I b i d . , 42 (1920), 2058.
