INDUSTRIAL A N D ENGINEERING CHEMISTRY
November, 1927
1291
Analysis of Mixtures of Aliphatic Nitrates b y Means of the Refractometer' By Wm. H. Rinkenbach PITTSBURGH EXPERIMENT STATION, U. S. BUREAUOF MINES,PITTSBURGH, PA.
T
HE recent introduction of the use of ethyleneglycol di-
nitrate and the probable future use of related nitrates in dynamites in conjunction with nitroglycerin presents a new and difficult problem in the analysis of such mixtures. This is due to the facts that a t present no chemical test for the detection of one in the presence of the others is known and also that, because of the differences in their vapor pressures, the usual procedure leading to their estimation by means of the nitrogen content of the mixture obtained by evaporating an ethereal extract cannot be used.
Indices of Mixtures of Ethyleneglycol Dinitrate a n d Nitroelvcerin Per cent ethyleneglycol dinitrate 17.35 33.71 49.17 61.93 79.23 Per cent nitroglycerin 8 2 . 6 5 66.29 50.83 38.07 20.77 n'," 1.4704 1.4651 1.4617 1.4581 1.4539 1.4634 1.4597 1.4562 1.4519 ny 1.4685 Table 11-Refractive
n y
1.4666
1.4617
1.4577
1.4543
1.4499
:z?
1.4646
1.4600
1.4556
1.4524
1.4579
T a b l e 111-Effect of Varying Proportions o n Refractive Indices of Mixtures of Ethyleneglycol Dinitrate a n d Nitroglycerin
ETHYLENEGLYCOL
DINITRATE
Tests on Pure Compounds
Studies2 of the properties of several members o f this class of compounds indicated the possibility of developing an analytical procedure based on the measurement of the refractive index of a mixture. Refractive indices of the pure compounds were first determined over a wide range of temperature for each substance, a curve was drawn which in each case proved to be a straight line, and values were read a t definite temperatures from this curve. (Table I) A Leitz refractometer equipped with a water jacket and a calibrated thermometer was used. The ethyleneglycol dinitrate and diethyleneglycol dinitrate have been described.2 The nitroglycerin was similarly prepared, kept in a vacuum desiccator for three weeks before use, and showed a nitrogen content of 18.35 per cent when analyzed by the nitrometer. The mixture of nitroglycerin and nitropolyglycerin was a commercial sample prepared by the usual method, containing 30 per cent of nitropolyglycerin and being free from oils, fats, and resins. The values may be considered accurate to the fourth decimal place.
--
P e r cent 0
10 20 30 40 50 60 70
80 90 100
NITROGLYCERIN
Per cent 100 90 80 70 60 50 40 30 20 10 0
n'," 1,4751 1.4722 1.4694 1.4666 1.4640 1.4613 1.4587 1.4562 1.4537 1.4513 1.4491
2; 1.4732 1.4703 1.4675 1.4648 1.4621 1.4595 1.4569 1.4544 1.4520 1.4496 1.4472
?LT 1.4713 1.4684 1.4656 1.4628 1,4601 1.4575 1.4548 1,4523 1.4498 1.4476 1.4454
These results show a maximum deviation of - 3 per cent of ethyleneglycol dinitrate, or 0.0008 in refractive index from the straight line connecting the 100 per cent values. They also represent a maximum deviation of *2 per cent or 0.0005 from any of the points by which the curves were determined. The values a t 15" C. came the nearest to giving a smooth curve passing through all points, and this may be considered the optimum temperature a t which to work. The foregoing gives a method by which the proportions of the glycol compounds in admixture with nitroglycerin or nitroglycerin and nitropolyglycerin may be determined with a fair degree of accuracy when the pure components Table I--Refractive Indices of Pure Compounds only are present. As such it is particularly applicable to ETHYLEBE DIETHYL-70% NITROGLYCERIN TEMPERA- ~YITROGLYCOLEKEGLYCOL 30% SITROPOLY- the analysis of nitrated mixtures in plant operation. TCRE
GLYCERIB
15.0 20.0 25.0 30.0
1.4751 1,4732 1.4713 1,4693
c.
DIBITRATE DINITRATE 1.4491 1.4472 1.4454 1.4435
1,4636 1.4517 1.4498 1.4479
GLYCERIB
Effect of Impurities 1.4767 1.4748 1.4728 1.4709
Inspection shows that the refractive indices of nitrates of the glycols are practically identical and much lower than those of nitroglycerin and the nitroglycerin-nitropolyglycerin mixture. Determination of the refractive index of a sample should give at least a qualitative indication of the presence of the glycol compounds. Tests with Mixtures
In order to make this method quantitative, mixtures of nitroglycerin and ethyleneglycol dinitrate were made up from accurately weighed portions of each and studied in the same manner as were the pure compounds. The curres derived gave the values in Table 11. Concentration-refractive index curves a t 15", 20", and 25 " C. were plotted from these values. It was found that the points were uniformly below a straight line joining the values for the pure compounds a t the given temperature. From the average curve drawn for each temperature the values in Table I11 were read off. Received June 3, 1927. Published with approval of the Director, U. S. Bureau of Mines. 8 THIS JOURNAL, 18, 1195 (1926); 19, 926 (1927). 1
The effect of the presence of a small amount of oi!y impurity, such as is found in ether extracts of dynamite, was next investigated A dynamite known to contain nitroglycerin but no nitropolyglycerin or ethyleneglycol dinitrate was extracted with ether in the usual manner. The extract was evaporated until all ether had been driven off under low pressure and a residue consisting of nitroglycerin and separated oils, fats, and resins was obtained. The nitroglycerin was separated by filtration a t 30" C. and studied by means of the refractometer. It was found that if the temperature was lowered to below 20" C. more oils, fats, and resins separated and obscured the field. The nitroglycerin was then chilled to 0' C., the precipitated oils, fats, and resins were filtered off, and the clear filtrate was studied under the refractometer. The two series of values were used to construct curves from which values a t regular temperature intervals were read off (Table IV). For purposes of comparison corresponding values for pure nitroglycerin are given. Indices of Pure a n d D y n a m i t e Nitroglycerin PURE DYNAMITE NITROGLYCERIN TEMPERATURE NITROGLYCERIN Before freezing After freezing ^ ^
Table IV-Refractive " L.
15.0 20.0 25.0 30.0
1.4751 1.4732 1.4713 1.4693
1.4819 1,4804 1.4781
1.4838 1.4820 1,4802 1.4783
INDUSTRIAL A N D ENGINEERING CHEMISTRY
1292
From this table it is evident that the application of the curves derived for mixtures of the Pure cornsounds to the interpretation of values obtained on dynamite extractives would give results indicating a proportion of nitroglycerin much higher than that actually present. It is also apparent that the oils, fats, and resins present in dynamite extractives cannot be removed entirely by freezing. Marqueyrol and Goute13 described a cryoscopic method of analysis for mixtures of nitroglycerin with ethyleneglycol dinitrate, but the writer has found that, while fairly accurate for mixtures of the pure substances, it yields very erroneous results when applied to mixtures extracted from commercial explosives. This was attributed to the impossibility of entirely removing oils, fats, and resins by freezing, as recommended by Marqueyrol and Goutel, and the data for refractive indices Bull. soc. chim., 2T, 443 (1920).
Vol. 19, No. 11
of such mixtures given above prove this conclusion to hold. Application of Method
Inasmuch as the oils naturally present in dynamite “dopes” vary eonsiderably and the types of greases used for graining purposes also vary to some extent, it is improbable that a satisfactory correction for the error caused by the presence of these substances could be determined and applied to a dynamite extractive. Accordingly, the application of the method and data, given in the case of commercial dynamites, must be restricted to the qualitative detection of the nitrates of the glycols. To the analysis of mixtures that have not dissolved oils and fats from other dynamite constituents, the method can be applied quantitatively, and so is of value in factory-control work.
Apparatus for Fractional Distillation under Reduced Pressur e’ By Jacque C. Morrell and Gustav Egloff UNIVBRSAL OIL PRODUCTS COMPANY,CHICAGO, ILL
EVERAL years ago the authors described a new form of apparatus for the fractional distillation of liquid mixtures under reduced pressure.2 The present contribution relates to a modification of this apparatus, which is more convenient in form for general laboratory use than the original apparatus. Figure 1 shows the front elevation of the modified apparatus. The receivers are mounted vertically a t the same elevation instead of being placed one directly above the other. The operation of the apparatus is similar to that of the original design. A three-way mercury-sealed stopcock (2) with large passageways controls the flow of the distillate to t h e r e c e i v e r s . When a fraction has collected in one of the receivers, stopcock (2) is turned so that the distillate flows to the other. Stopcock (4),also a threew a y s t o p c o c k , is then opened to the atmosphere and closed to the equalizing or stabilizing reservoir connected to the vacuum pump. This change permits the w i t h d r a w a l of the fraction from the receiver through the draw-off stopcock (3). The second fraction is collected and withdrawn similarly. After a fraction has been removed the receiver is g r a d u a l l y
S
1 Received July 1, 1927. Presented before the Division of Petroleum Chemistry at the 74th Meetina of the American Chemical Society, Detroit, Mich., Septemter 5 to 10, 1927. 9 J . SOC. Chcm I n d . , 42, 188T
connected with the stabilizing reservoir by means of stopcock (4) to reduce the pressure to that of the system. Figure 2 is a side elevation of the same apparatus that shows more clearly the arrangement of the equalizing bottle (5) and the stopcocks (4) for connecting the receiver with the system or the atmosphere. Acknowledgment
The writers wish to acknowledge a suggestion of 13. M. McClure, formerly of this laboratory, in the conversion of the original apparatus t o the present form.
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