1065
V O L U M E 20, NO. 11, N O V E M B E R 1 9 4 8 in the specific gravity of benzene (0.879) and hexane (0.660) was investigated. In order to measure the specific gravity by means of a Westphal balance, a minimum of 25 ml. of liquid is necessary. Mixtures of 20 ml. of 80% alcohol (containing added benzene) and 25 ml. of saturated salt solution were extracted with 25-ml. portions of hexane, and the specific gravities of the latter were measured. The results obtained were slightly lower than the calculated values. The hexane extract was therefore first washed with two 25-ml. portions of water to remove dissolved alcohol, followed by a final wash with 25 ml. of saturated salt solution. The specific gravities of the extracted hexane were then found to agree closely with the calculated ones. A typical specific gravity-concentration Figure 2.
graph is shown in
Apparatus and Reagents. The apparatus and reagents required for this determination are the same as listed under the refractive index method, except that a Westphal-type balance is substituted for the refractometer. I n the authors' work, a Christian Becker Chain-0-matic specific gravity balance, Catalog KO.110, range zero to 2.000, standardized a t 20' C., was used. Procedure. Dilute the alcohol sample, distill as described under the refractive index method, and transfer the distillate to a 250-ml. Squibb separatory funnel. Add 25 ml. of saturated salt solution and 25.0 ml. of hexane, stopper the funnel, and shake vigorouslv for 30 seconds. After the two layers have separated, discard the aqueous layer. Wash the hexane with two 50-ml. portions of water (three if ether is suspected t o be present) and finally with 25 ml. of saturated salt solution. Transfer the hexane layer to a 25-ml. cylinder and determine its specific gravity a t 20°/20" C. If the determination is made a t a higher temperature, add 0.00086 per 1' C. From the corrected reading subtract the specific gravity of the hexane itself a t 20"/20" C., and from
the graph, prepared by applying the foregoing procedure to known mixtures, read the concentration of benzene in the sample. Analysis of Known Mixtures. The foregoing method, including the distillation step, was used to analyze several known mixtures of alcohol-benzene, some of which contained added ether (Table IV). The results possess the same accuracy as those found by the distillation-refractive index procedure. SUMMARY
The method of Babington and Tingle for benzene in alcohol gave results which were considerably too high. Furthermore, it was shown that the chemistry of their method is unsound. Two methods for the determination of benzene in alcohol, accurate within 0.02% of the volume of the sample, have been developed. One depends on the difference between the refractive indices of benzene and hexane, and the other depends on the difference between their specific gravities. A small amount of ether does not interfere. ACKNOWLEDGMENT
The authors wish to thank E. B. Spaulding and Floyd Diephuis, formerly of the Badger Ordnance Works, now a t the Parlin, S . J., plant and Experiment Station, respectively, for helpful suggestions regarding the method. LITERATURE CITED
(1) Atkins, W. R. G., Nature, 151, 449 (1943). (2) Babington, F. IF'., and Tingle, Alfred, J . Ind. Eng. Chern., 11, 556 (1919). (3) Baernstein, H. D., IXD. ENG.GREY., ANAL.ED.,15, 251 (1943). (4) Dolin. B. H., Ibid., 15, 242 (1943).
RECEIVED February 9, 1947.
Determination of Small Amounts of Benzene in Ethyl Ether S. L. R.IIREL1, D. L. KOUBA, AND W. W. BECKER Hercules Experiment Station, Hercules Powder Company, W'ilmington 99, Del. Small amounts of benzene (0.2 to 1.2'70) in ether may be determined within 0.05% of the volume of the sample by making use of the difference in the specific gravities of benzene (0.879) and ether (0.720). The benzene is concentrated in about one third of the ether by distillation, and the specific gravity of the residue is determined.
I
S CONSECTIOS with the operation of ordnance plant3
Advantage was taken of the considerable difference between the specific gravit,ies of benzene (0.879) and ether (0.720). The method consists in distilling off about tn-o thirds of the ether to concentrate the benzene, measuring the specific gravity of the residue, and reading its benzene content from a graph prepared by using known mixtures. The results, expressed as per cent benzene, are acAnalysis of Known Benzene-Ether Solutions and Plant-Rectified Ether curate xithin 0.05 unit. Benzene in Benzene Difference The general principle of this Benzene Specific Distillation Found in between Residue Sample, Added, Gravity Volume of .$mounts procedure was developed to Volume of Residue Residue after (Read from Volume Present Basis a t 2Oo/2O0 C. Distillation B , Fig. 1) Basis a n d Found determine small amounts of 9% M1. % % % benzene in alcohol (1).
manufacturing solvent types of smokeless powder during World K a r 11, a method was desired for determining small amounts of benzene in ethyl ether, which had been manufactured from 2B ethyl alcohol containing 0.5% benzene.
Table I.
Sample la
2a 3 3 4 4 4 6
a b
0.40 0.60
0:sia 01666
0.86b
0.7207 0.7218 0.7202 0.7220 0.7212 0.7223 0.7230 0.7211 0,7222
5 0:63b Known benzene-ether solution. Includes original benzene determined previously.
44.5 44.5 47.0 47.0 43.5 41.0 46.5 41.5 42.5
1.31 1.96 1.00 2.08 1.60 2.27 2.70 1.54 2.21.
0.39 0.58 0.31 0.65 0.46 0.62 0.84 0.43 0.63
-0.01 -0.02
+0:04 ,.. -0.04 -0.02
...
EXPERIMENTAL
In evaluating the specific gravity method, small amounts
0.00 1 Present address, F. 0. Pierce Company, Long Island City,
K. Y.
ANALYTICAL CHEMISTRY
1066 (0.2 to 1.2%) of benzene were added from a microburet to 50 ml. of ether, the solutions shaken with 50 ml. of saturated sodium chloride solution, and the specific gravities measured. The values were found to lie on a reasonably straight line ( A , Figure 1). As certain plant' samples of ether contained amounts of benGene that were below the sensitivity of the method, concentration by distillation was attempted. Solutions consisting of 150 ml. of ether containing added benzene were concentrated to approximately 50 ml. by distillation and then the specific gravities of the residues were measured. The values plotted in B , Figure 1, sho17 that a slight loss of benzene occurs. It is, therefore, advisable for each analyst to distill known solutions in his apparatus, construct his own graph, and use it in calculating the benzene content of samples. Apparatus. The distillation apparatus is similar to that described by Shaefer (W), except that a 2-liter suction flask containing a 100-ml. test tube is used as a receiver for the distillate. Procedure. Measure a 150 nil. sample of the ether into a 500nil. round-bottomed flask. Attach the flask t o a 3-bulb Snyder column, condenser, and receiving flask containing a large test tube marked a t the 100-ml. point. Direct a moderately strong current of compressed air against the lower bulb of the column. Distill 100 ml. of the ether a t the rate of 2 to 3 drops per second and discard it. Cool the flask and transfer the residual ether to a 250-ml. Squibb separatory funnel, add 50 ml. of saturated sodium chloride solution, stopper the funnel, and shake vigorously for 30 seconds. Allow the t'wo layers to separate and discard the aqueous layer. Rash the ether with two more 50-ml. portions of salt solution to remove any alcohol present. Transfer the ether layer to a 50-ml. graduated cylinder, read the volume, and measure the specific gravity a t 20"/20" C. If measured a t a higher temperature, add 0.0011 per 1' C. From a graph prepared after distilling known mixtures of cther and benzene, read the per cent benzene in the distillation residue. Calculate the per cent benzene in the original sample by the following equation: Volume of residue X
yobenzene in residue 150
0.72
0 $72
2 0
,\" 0 7 2 N
t >
2
072
5 u
'Y
072 -0-
w 0.71
0.71
--A--CURVE B-RESIDUES L E F T A F T E R D I S T I L L A T I O N OF KNOWN SOLUTIONS
I
I
0 5
I O
PERCENT
The foregoing procedure was applied to two known solutions of ether and benzene which contained 1% each of water and
I 5
I
I
2.0
2.5
BENZENE
Figure 1. Concentration of Benzene in Ether us. Specific Gravity of Benzene-Ether Solution
alcohol. Typical plant-rectified samples are known to contain small amounts of these substances. The method was also applied to three samples of plant-rectified ether, both as received and after the addition of known amounts of benzene (Table I). ACKNOWLEDGMENT
Most of the experimental work described in this art.icle was carried out a t the Radford Ordnance Works, operated by the Hercules Powder Company.
70 benzene, by volume RESULTS
CURVE A- KNOWN SOLUTIONS WITHOUT D I S T I L L A T I O N
LlTERATURE CITED
(1) Kouba, D.
L.,Kangas, L. R.,and Becker, W. W., ANAL.CHEM.,
20,1063 (1948). (2) Shaefer, W. E., IXD. ENG.CHEM., ANAL.ED.,16,432 (1944).
RECEIVED February 9, 1947.
Determination of Diethyl Phthalate in Smokeless Powder P. G. BUTTS', G. B. PRINE2, D. L. KOUBA, AND W. W. BECKER Hercules Experiment Station, Hercules Powder Company, Wilmington 99, Del. Diethyl phthalate in solventless type smokeless powder can be determined by digesting a sample with potassium hydroxide and hydrogen peroxide, distilling from the reaction mixture the ethyl alcohol so formed, and determining the ethyl alcohol in the distillate by oxidation with potassium dichromate.
0
NE of the constituents added to certain types of solventless smokeless powder is diethyl phthalate. During World War 11, a rapid and accurate method was needed for its determination. Before the war the only available direct procedure was the Thames oxidation method ( 2 ) which, essentially, consists in digesting a 5.0-gram sample with 40% (1 to 1) nitric acid, whereby the nitrocellulose is hydrolyzed to a water-soluble form and the phthalic ester is converted to phthalic acid. After 1 Present address, Department of Chemistry, Purdue University, Lafayette. Ind. 4 Present address, Columbia Powder Company, Tacoma, Wash.
oxidation of the oxalic acid (formed by oxidation of the cellulose) with potassium permanganate, lead acetate is added in order t o precipitate lead phthalate. This precipitate is filtered, dissolved in nitric acid, and treated with sulfuric acid. The resulting precipitate of lead sulfate is filtered, dried, and weighed, and the percentage of diethyl phthalate is calculated. When Smith and Strempfer (I) used lead acetate as a precipitating agent, they obtained high results, which they attributed to contamination of the precipitate with varying amounts of basic lead acetate. When lead acetate was added to known amounts of phthalic acid, the analytical values obtained for phthalic acid were 3Iy'
