I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
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Vol. 16. No. 9
A New Correction Tube for Gas Burets’ By F. C. Vilbrandt UNIVERSITY OB NORTH CAROLINA. CHAPELHILL, N. C.
T
HE usual variations in temperature and pressure that take place during the course of an analysis of a gas entail an excessive amount of calculation in order to prevent errors. To obviate these numerous calculations many of the commercial sets of standard laboratory design are fitted with compensating tubes of the Peterssen2 type attached to the measuring burets. All readings of volumes are thus rendered to a comparable basis, either to volumes under standard conditions of temperature and pressure (760 mm. pressure and 0” C.) or to readings that are compensated for any changes in temperature and pressure taking place during the course of the analysis. The original correction tube of Hempe13consisted of a candelabra-shaped arrangement of three arms, too bulky to enclose any part of it in the water jacket with the buret used for measuring the gas. Petermen’s tube2 is constructed so that the gas enclosed in the correction tube is at the same temperature as the gas being measured, but the construction of the manometer in this apparatus is such as to make it extend outside of the water jacket. It is under strain D and easily broken. To build it so the manometer will be in the jacket would C= require a very large, unwieldy apparatus. The author has used the Peterssen tube for a number of years and, aside from the foregoing objections, has found it a very useful and reliable Cadjunct to the measuring buret in gas analysis. Attempts to instruct students and assistants in the use of this apparatus have amplified its weaknesses-that is, ease in breaking off the manometer, which is under strain, and the frequent recalibration due to breakage. This difficulty can be overcome by modifying the correction tube and manometer in such a manner that the entire apparatus can be enclosed in the water jacket holding the gas buret, with all strains in the apparatus eliminated. FIG.1
APPARATUS The Compensating tube, A (Fig. l), has sealed into it, opening below, a tube, C, which serves as the maliometer in place of the reverse U-shaped arrangement of Peterssen. Mercury in the well a t the bottom of the compensator A seals off the gas enclosed in it from the gas in communication with the buret. Changes in temperature and pressure cause the mercury in C to rise or fall when in communication with the gas in the measuring buret. $ince this apparatus is submerged in the same water in the jacket as the measuring buret, H, no difference in temperature exists between the gas to be measured and the gas enclosed in the compensator A , CompensaReceived January 28, 1924. Chcm., 26, 467 (1886). Gas Analysis,” 1002, p. 94. millan Co., New York. 1
* 2. anal.
* Hempel-Dennis, “Methods of
The Mac-
tions are made for the difference in pressure by forcing more or less gas into the part of the compensator in communication with the gas in the measuring buret by raising or lowering the level bulb on the measuring buret so that the level of the mercury meniscus reaches some point, F. I n the same way as the Peterssen apparatus provides for excessive pressure or vacuum in the compensator, by carelessly bringing the gas in the measuring buret in communication with the compensator, two reservoirs, B and B‘, are provided at the top and bottom of the capillary, C. If these reservoirs are not provided, the adjustment of the mercury column might be thrown out by carelessness. When the apparatus is to be used only for compensating changes in temperature and pressure which occur during the course of an analysis, the side arm, G, is unnecessary. To adjust under these condftions, an amount of air is forced into the space in tube A through the mercury in the wall a t the bottom of C, sufficient to raise the level of the mercury in C to some etched mark on this capillary. The tube C should be made from tubing with marks etched upon it. It is usually rather difficult to set a mercury meniscus accurately to some predetermined etched mark, so by using a previously graduated tube, as suggested above, a mark to be selected and used for the compensating mark can be readily obtained without laboriously striving to bring it to a desired mark. When readings are desired to read to volumes under standard conditions, a small side arm is sealed onto the compensating tube A to permit ready forcing of air into this chamber to bring the mercury level to the proper point, after the usual calculations for differences in temperature and pressures have been made according to the procedure used in adjusting and calibrating the Peterssen tube.4 After the proper precautions and calculations have been made the side arm, G, is sealed off. It may be advisable to seal a stopcock onto the side arm to permit the tube to be cleaned with greater ease, but the necessity of cleaning is. never great if clean mercury is used and if care is exercised in manipulation to prevent any corrosive gases from entering the compensator. A stopcock on the side arm, however, detracts. from the adaptability of the compensator in that it prevents its. insertion in its entirety into the water jacket along with the measuring buret. The volumes of B and B‘ depend largely upon the volume of the measuring buret to which it is to be attached. T h e y must be of sufficient size to take care of the difference in expansion or contraction that gases undergo during the use of the equipment, together with a small additional volume as a factor of safety so that readjustments and recalculations. due to careless manipulation of the compensator need not be so frequent. This is no different from the precautions called for in the use of the Peterssen apparatus. This compensating device can be made in lengths suitable. to the water jacket and measuring buret to be used with it. It simplicity, ease of manipulation and construction, compactness, flexibility, comparative ruggedness, and inexpensiveness suggest its use, not only for laboratory gas analysis sets, but also for the portable field sets with but a minor change at the top of the measuring buret with which the present sets are provided-i. e., sealing on a 2-way stopcock and attaching; 4
Dennis, “Gas Analysis,” 1918, p. 94. The Macmillan Co.,New York.
I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
September, 1924
the compensating device a t this point, using a slightly larger water jacket to enable inserting the compensator alongside the measuring tube. The accuracy of the single column mercury meniscus used
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in this apparatus is as great as that of the 2-level adjustment used on the Petermen tube, and much more delicate and accurate than the wide 2-bulb Tutwiler modification of the Petermen compensator.
Solubility of the Petroleum Hydrocarbons' By C. F. Mabery CASESCHOOL OF APPLIEDSCIENCE, CLEVELAND, OHIO
B
ESIDES the solubility of the petroleum hydrocarbons in one another, they are generally characterized by insolubility under different conditions in single solvents. It is only with variable mixtures of ether, in which, except the last residues of the asphaltic crudes, these hydrocarbons are all extremely soluble, and alcohol, in which they are a t most only slightly soluble, that efficient solvents may be made capable of a good separation of the homologs andisologs. A method of separation based on these differences in solubility was employed as described in an earlier paper on this subject.2 While the results then presented were sufficient to indicate wide variations in solubility, no attempts were made in that work to show precisely these differences in the hydrocarbons separated. I n taking up the study of the Midcontinental oils-using this term in a broad sense to include Oklahoma, Wyoming, Illinois, and Ohio crudes-and other southern oils, it seemed desirable to ascertain with greater precision the extent to which this method may be relied on for the separation of the individual hydrocarbons. By reference to the paper cited it appears that, starting with a given quantity of oil, the solvent dissolves out first in successive portions all the series, graduated in solubility, and after a sufficient number of repetitions the fractions show a similar graduation in physical properties. Then from this mixture of homologs and isologs, with the use of a properly graded solvent, the isologs, the lighter D-hydrocarbons, may be fractionated from the less soluble homologs, the H-hydrocarbons.
METHODS The solvent was tried in two formsether 50, alcohol 50; and ether 100, alcohol 50, by volume; the former on fractions in the most soluble end, and the latter on the fractions of the least soluble end. For the manipulation of the solution two common test tubes with side tubes were used, as shown in the figure. I n the tube B, closed by a cork and rubber cap, a quantity of the oil with ---the solvent was allowed to stand a t 20" -C. for 2 hours, or until it settled clear after sufficient agitation. The tube A , also closed with a stopper and cap, was weighed, cooled to the same temperature, attached to the tube B as shown, and after a portion of the solution in tube B was decanted into it, again closed with its cap and weighed. The cork and cap were then removed and this tube was heated in an air bath to 110" C. for the removal of the solvent and moisture (from the solvent), and the tube and oil weighed. By this means it was possible to prepare and weigh a saturated solution of the solvent without loss. ~~~
1
Received July 7, 1924.
* Mabery, THISJOURNAL,
16, 1233 (1923).
I n making the saturated solutions care is necessary in limiting the amount of the oil, especially in the 100-50 solvent, for a large excess of the oil is liable to dissolve the ether away from the alcohol. On this account the solubility of the Cabin Creek Fraction D-7 in the 100-50 solvent could not be determined. This often happens in extractions with too rich a solvent. The addition of more alcohol attracts the ether from the oil so quickly that the stopper may be blown out of the bottle.
RESULTS The results obtained by this method are recorded in the table, which includes fractions of the oils described in the former paper together with those from an Oklahoma oil and from a Gulf Coast, Texas, oil. From the last two oils, a description of which has not been published, fractions were separated from distillates, -300" C. 30 mm., and from residues of these distillates. As in the earlier paper, the numbers of the fractions are taken from the H and D series, No. 1, the most soluble end, to No. 10 or 13, the least soluble end. SOLUBILITY OF THE PETROLBUM HYDROCARBONS Composition of sol- Solubilty Fraction vent, ether-alcohol Per cent 4.33 H-2 50-50 Cabin Creek (f300' C., 30 mm.) 15.86 D-2 2.19 H-7 4.86 D-7 42.53 100- 50 H-7 9.60 D-7 (Ether dissolved by oil) 6.10 H-1 50-50 Rosenbury ($300' C., 30 mm.) 19.45 D-1 4.64 H-5 11.26 D-5 7.25 H-2 Mecca (+30O0 C., 30 mm.) 9.66 D-2 7.58 100-50 H-7 13.53 D-7 Sour Lake, Texas (+300° C., 7.26 50-50 H- 2 30 mm.) 16.66 D-2 7.27 50-50 H-5 22.04 D-5 10.52 100-50 H-5 25.62 D-5 12.55 5C-50 H-I. Russian (+300° C., 30 mm.) 17.60 D-1 3.25 100-50 H-5 6.94 D-5 28.27 H-2 Oklahoma (-300' C., 30 mm.) 35.30 D-2 12.22 H-9 30.39 D-9 50-50 8.40 H-2 Oklahoma (+300° C.,30 mm.) 16.54 D-2 4.72 H-13 6.82 D-13 11.00 100-50 H-13 15.82 D-13 Gulf Coast, Texas (-300' C., 20.24 60-50 H-2 30 mm.) 29.28 D-2 9.83 50-50 H-8 15.54 D-8 9.16 H-2 Gulf Coast (+300° C . , 30 mm.) 18.84 D-2 6.52 H-10 12.20 D-10 4.73 100-50 H-13 9.57 D-13
