ANALYTICAL
326
bulb. According to Midgley (S), this material is very effective as a boiling stone. The fact that the vapors, after boiling from the liquid, immediately come in contact with the relatively hotter walls of the distilling bulb prevents their partial condensation. In consequence, the distillation of condensed gases parallels a simple batch distillation without fractionation much more closely than the ordinary A. S. T. M. distillation, in which the temperature of the walls of the distilling bulb above the boiling liquid is below its dew point. There are, however, certain details in which the experimental procedure does not exactly follow the mechanism assumed in the calculation. The separation of methane from the ternary mixture involves the loss of a certain amount of ethylene from the ethanes fraction. This would tend to depress the front end of the curve. Moreover, the distillation curve is constructed from readings of the increase in pressure of the overhead gas in a receiving bulb, and therefore represents the percentage of the material finally recovered in the receiver. The graph, however, is constructed on the basis of per cent evaporated from the condensed sample in the distilling bulb. An error is, therefore, introduced by the amount of gas which fills the distilling bulb a t atmospheric pressure, before any sample is collected. Furthermore, a lag exists in the thermocouple readings. These conditions, in addition to the approximate nature of the assumptions made in calculation of the master graph will cause discrepancies between the predicted and observed analyses. APPLICATION OF METHOD Several typical analyses of dry refinery gases are presented in the accompanying table for comparison with the fractional distillation method. These gases are derived a t 25 per cent from crude still operation, 25 per cent from vapor phase cracking in a DeFlorez unit, and 50 per cent from liquid phase cracking in Cross units.
CONBTITUBINT
RUN 1 PodbjelShort niak cut
RUN 2 PodbielShort niak cut
Fixed gaa and methane Ethanes Propanes Butanes
39.4 24.0 26.4 11.2
1.3 10.5 56.1 32.1
38.2 23.2 28.1 10.5
1.1 12.0 57.2 27.9
RUN3 PodbielShort niak cut
.
36.5 18.0 24.8 20.7
34.8 20.4 26.6 18.2
The reasons for this inconsistency are believed due as much t o variations from day to day of the composition of the closeboiling fractions contained in the refinery gases and to errors in experimental observation as to the inadequacy of theoretical treatment The data on hand a t present indicate that the percentages of ethanes predicted from the master graph are about 2 per cent too high. Likewise, the butanes predicted are about 2 per cent lower than actually obtained in a fractional analysis. Since the accuracy with which the analyses may be performed is not much greater than this deviation, no correction has been incorporated into the master graph. When sufficient data become available to establish definitely this trend of deviation, it may be readily taken into consideration by changing the relative position of the constructed “grid” and the coordinates of Figure 1. While not as accurate as the best fractional distillation analysis, the short-cut method with the simplification presented is well adapted to routine analysis for plant and laboratory. The method of preparing a master graph indicated above is believed to be quite as satisfactory for this type of work as that based on experimental data for synthetic mixtures of pure paraffin hydrocarbons, and presents the advantage of an appreciable saving of time and expensive chemicals. It is planned to extend the application of the Rayleigh equaI
Vol. 6, No. 5
EDITION
tion to mixtures containing pentanes. This would make the correlation applicable, not only to dry gases, but to practically all but the heaviest refinery gases.
(1)
LITERATURE CITED Copson, R. L., and Frolich, P. K., IND. ENG. CHEM.,21,
1116
(1929).
(2) Davis, H. S., and Daugherty, J. P., I b i d . , Anal. Ed., 4, 193 (1932). (3) Midgley, T., Jr., I b i d . , 1, 86 (1929). (4) Oberfell, G. G . , and Alden, R. C., Oil Gas J.,27, No. 22, 142 (1928). ( 5 ) Podbielniak, W. J., IND.ENQ.CHEM.,Anal. Ed., 3, 177 (1931). (6) Rosen, R., and Robertson, A. E., Ibid., 3, 284 (1931). (7) Schaufelberger, W. M., Oil Gas J., 29, No. 16, 46 (1930).
(8) Walker, Lewis, and McAdams, “Principles of Chemical Engineering,” 2nd ed., pp. 598,731, MoGraw-Hill Book Co., N. Y., 1927. RBCEIVHlD
September 2, 1933.
Self-Filling Pipet for Dispensing Hot Caustic Solutions CLIFFORD J. B. THOR Bureau of Plant Industry, Austin, Texas
A“
ORDINARY pipet modified as shown in Figure 1 greatly facilitates manipulation of the hot ferric sulfatesulfuric acid solution used in the permanganate method for determining copper reduced in the various methods of sugar analysis. For this specific purpose, the lower tube of a 50cc. pipet was cut off near the bulb and the new outlet firepolished until the opening was of suitable size (about 3 mm.). The bends in the upper tube were easily made after heating with an ordinary Tying-top burner. The 50-cc. pipet operates satisfactorily when the solution is contained in a 2-liter Pyrex beaker which can conveniently be heated by means of a small e l e c t r i c hot plate. The pipet is placed in the s o l u t i o n in a position similar to that -...:::sshown by the dotted lines. It sinks gradually as the - bulb fills and eventually assumes the position shown in solid l i n e . T h e latter position perm i t s removal of a V large proportion of FIGURE 1. SELF-FILLING PIPET t h e l i a u i d in t h e beaker ‘before refilling is necessary. When the liquid is to be dispensed, the filled pipet is best twisted so the bulb is vertical. When dissolving cuprous oxide which has been collected on an asbestos mat in a Gooch crucible, it is convenient to loosen the mat with a pointed glass rod, transfer the bulk of it to a 250-cc. beaker, and finally wash down the inside of the crucible with the stream of hot acid solution from the pipet. If such a pipet were to be made specially to deliver a more exact and predetermined volume of liquid, it would undoubtedly be desirable to attach the upper tube near point X since air bubbles tend to collect there when the level of liquid in the beaker becomes low. RECBIVED April 19, 1934.
