636
INDUSTRIAL AND ENGINEERING CHEMISTRY
by 0.9 mm. of mercury. Higher sensitivity is possible by decreasing the ratio d / D , say, by decreasing the size of the orifice. However, the size of the orifice limits the capacity of gas removal from the system, so that increased sensitivity by decreasing the size of the orifice is obtained a t the expense of decreased capacity. In Figure 3, the rate of gas flow is plotted from a suitable orifice flow equation (Fliegner’s equation) modified to include the molecular weight of the gas, although otherwise based on air flow.
.
A representative example is shown by the dotted lines on the chart for:
P = 120 mm. of mercury, d = 1.25 mm. for air flow
(IN= 29)
Starting a t the value of P, the path proceeds vertically to the 45 a line corresponding to the molecular weight of the gas ( air is shown by the hcavy line), then horizontally to the d = 0.1-mm. axis. From here the path follows an oblique line until it intersects the vertical line corresponding to the value of d , and finally horizontally to give the rate of gas flow of 1.3 liters per minute a t standard temp,.rature and pressure (S.T.P. = 0’ C. and 760 mm. of mercury pressure). Thus, by means of these charts, the dimensions of the device may be chosen to give desired characteristics within very wide ranges. These charts do not extend below a pressure of 1 mm. of mercury, because for lower pressures new factors controlling both the sensitivity and rate of gas flow are introduced. Thus, the rate of gas flow equation has to be modified by lower discharge orifice coefficients due to change-over from turbulent to viscous flox. Moreover, the sensitivity of the device becomes dependent upon the relative motion of the float, which is adequate a t pres-
Determination
Vol. 18, No. 10
sures above about 1 mm. of mercury; below this pressure, modifications in design are needed to magnify the displacement of the float. CONCLUSIONS
The simplicity of this type of manostat and the ease v,Tith which it may be designed t o meet a wide range of requirements make it ideal for practically all laboratory needs in place of complicated electrical hookups. Built of heavy glass or metal, the unit may be easily adapted for superatmospheric pressures. Furthermore, by suitable design, the device may be used for large industrial applications IT-henever constant-pressure conditions must be maintained automatically. Certain modifications of the device may also be made, so that it is more suitable for very low pressure, and in which it is also a direct-reading semivacuum gage. These modifications are still in the process of development and will be discussed in a subsequent paper. ACKNOWLEDGMENTS
Thanks are due J. P. Bader of the Emil Greiner Co. for his valuable suggestions in preparing the charts, and for permission to publish them. The helpful suggestions of D. F. Othmer of the Polytechnic Institute of Brooklyn are deeply appreciated. LITERATURE CITED
(1) Caswell,Phil.Trans., 24,1597 (1704). (2) Dubrovin, J.,Instruments, 6, 194 (1933). (3) Gerrnann, F. E. E., and Gagos. K. A , , IND.ENQ.CHEM.,ANAL.ED. 15, 285 (1943).
OF
Some Aromatic Amines and Substituted Ureas in Smokeless Powder
Improved
Volumetric
Bromination
Procedure
THOMAS D. WAUGH, GARMAN HARBOTTLE, AND RICHARD M. NOYES, California Institute of Technology, Pasadena, Calif. The volumetric bromination procedure which is in general use for the estimation of stabilizers in smokeless powder has been modified b y the use of glacial acetic acid as a solvent for the sample to be brominated. The modified procedure is more convenient than the standard procedure in which carbon tetrachloride iP’ used in a two-phase system, and less dependent on conditions of bromination than the standard procedure in which alcohol i s used as the solvent.
F
OR the quantitative determination of stabilizers in smokeless powders a volumetric bromination procedure has been widely used in preference to gravimetric procedures, which are generally more time-consuming. The volumetric bromination procedure involves treatment of a solution of a powder extract with a known amount of standard bromate-bromide solution, acidification to liberate bromine, addition of iodide in excess a t the end of the bromination period, and titration of the free iodine with standard thiosulfate solution with the use of starch as indicator. This procedure has been used in the determination of diphenylamine, ethyl centralite (A-,A-’diethyl-N,N’-diphenylurea), and acardite (N,Ndiphenylurea). Under the conditions of the procedure 1 molecule of diphenylamine reacts with 4 molecules of bromine, and 1molecule of ethyl centralite or acardite reacts with 2. In the procedure as developed fur centralite by Levenson (g), the bromination and titration are carried out in a one-phase solution in the presence of ethyl alcohol to keep the stabilizer in solu-
tion, under carefully controlled conditions of temperature and time in order to obtain quantitative bromination of the stabilizer without accompanying side reactions between the bromine and the alcohol. In order to eliminate the necessity for such precise control a procedure employing carbon tetrachloride as a solvent for the stabilizer was developed by Ellington and Beard (1). Carbon tetrachloride is nonreactive to bromine, so that conditions of bromination are much less critical than in the alcohol procedure. The manipulations are somewhat cumbersome, however, because the two-phase system must be shaken frequently during bromination and titration. Both the alcohol procedure and the carbon tetrachloride procedure are in common use for the estimation of diphenylamine and centralite in smokeless powders. The authors have found that the advantages of both procedures may be obtained in a procedure in which glacial acetic acid is used as the solvent for the substances to be brominated. Acetic acid is nonreactive to bromine; moreover, its use permits the bromination and titration to be carried out in a single phase. Accordingly, they have developed a procedure involving the use of acetic acid and have tested this procedure by determinations of ethyl centralite, diphenylamine, and acardite. Most procedures for the estimation of stabilizers in smokeless powder involve extracting the powder sample directly with ether or else decomposing the sample with alkali, distilling the stabilizer with steam, and extracting the distillate with ether; the re-
ANALYTICAL EDITION
October, 1946 Table
Stabilizer E t h y l centralite
hlethod H04c
I. Analysis of Pure Samples of Stabilizers
Time of Bromination, Minutes 5 1 45 see.
Temperature of Bromination, O
c.
Room
WC. .. . ...
Alcohol CClC Diphenylamine Acardite
HOAc
CC14 KOAc CClr
Table
15 see. 45 eec. a
15-20 Room Room Room Room
1 5
10 5
1 3 hours 5
Room
P e r C e n t of Sample Detected Individual determinations Bverage 101,5,101 . O , 102.0,102.8 101.8 100.2,99.9,99.8,100.0 100.0 99.8 99.8 99.5 99.5 99.3 99.3 99.3,99.6,99.7,99.2 99.5 99.8,99.8,98.3. 100.7, 99.8 99.9,99.6, 100.8, 99.3,99.6 99.9,99.0 99.4 99.6,99.8,99.2,99.9 99.6 99.0 99.0 99.1,98.3 98.7 83.6 84.5,8 2 . 8 81.3 81.3 30.9 30.9
637 TITRATION.At the end of this time 10 ml. of 15% potassium iodide solution are added, the flask is swirled, and the gutter and walls arc washed down with distilled water from a xash bottle. The solution is titrated immediately with 0.05 A‘ sodium thiosulfate solution. Five milliliters of 0.5% starch solution arc added when the solution has assumed a light yellow color, and the titration is continued to the disappearance of the blue color. A blank determination is made, under the same conditions of bromination and titration, on a 60-ml. portion of glacial acetic acid. The percentage of stabilizer in the powder sample is calculated by means of the equation
II. Comparative Analyses of a Nitroglycerin Propellant for Ethyl Cenhalite
Centralite
Av.
Percentage of stabilizer =
Carbon Tetrachloride
.4cetic Acid
70
70
0.986 0.997
0.971 0,973 0.978 0.981 0.976
0,992
sulting ether solution is evaporated, and the residue from the evaporation is analyzed for stabilizer. The authors have found that the use of these procedures on samples that were subsequently analyzed for ethyl centralite or diphenylamine by the carbon tetrachloride bromination procedure frequently led t o results which were low by as much as 10% of the stabilizer present. Subsequent studies indicated that the discrepancies were due to the presence of difficultly volatile peroxides in the ether. The replacement of ether by methylene chloride as an extracting solvent eliminated the discrepancy entirely and led to satisfactory results. Accordingly its use is recommended in the procedure given below. PROCEDURE
This procedure may be used when diphenylamine, centralite, or acardite are present in a smokeless powder in the absence of other substances that react with bromine. Xtroglycerin and diethyl phthalate do not interfere. When more than one stabilizer is present in a given powder, a more involved procedure than the one given below must be used. REAGENTS.Standard 0,1000 iY bromate-bromide solution is prepared by dissolving 2.784 grams of recrystallized potassium bromate (dried to constant weight at 110” C.) and 15 grams of potassium bromide in distilled water and diluting to 1 liter in a volumetric flask. Standard 0.05 N sodium thiosulfate solution, 0.5y0starch indicator solution, and a 15% solution of potassium iodide are prepared according to standard iodometric practice (3). The methylene chloride used for extraction is distilled from technical grade material; adequate head and tail fractions are discarded. Reagent grade glacial acetic acid is used in the bromination procedure. A sample of powder conEXTRACTION AND BROMINATION. taining not more than 0.075 gram of ethyl centralite, 0.02 gram of diphenylamine, or 0.06 gram of acardite is finely divided and introduced into a Soxhlet extraction apparatus, which is attached to a 250-ml. glass-stoppered iodination flask containing 100 ml. of methylene chloride. The sample is extracted for 2 hours or more depending on its state of subdfvision. The flask is then detached and the methylene chloride is completely evaporated by means of a stream of dry air, with suitable precautions to minimize the hazard due to possible detonation of the nitroglycerin in the extract. The residue is dissolved by the addition of 60 ml. of glacial acetic acid, and 26.00 ml. of 0.1000 N bromate-bromide solution are added with a pipet. Five milliliters of concentrated hydroch1ori.c acid are added, the flask is stoppered, and the contents are mixed by swirling. The bromination is allowed to proceed for 1 * 0.25 minutes from the time the solution was acidified if centralite or diphenylamine are being determined, or at least 5 minutes in the case of acardite.
(1 - A / B ) IYVC
w
in which A = volume of thiosulfate consumed in titration of sample B = volume in milliliters of thiosulfate solution consumed in titration of blank 11’ = normality of standard bromate-bromide solution V = volume of pipet in milliliters W = weight of powder sample in grams C = one tenth of equivalent weight of stabilizer; 6.709 for centralite, 2.115 for diphenylamine, and 5.306 for acardite The nitroglycerin remaining in the solution at the end of the titration should be destroyed by boiling with an excess of ferrous chloride or by some other appropriate procedure. RESULTS
The accuracy and precision of the new method and the effect of time of bromination were determined by analysis of purified samples of ethyl centralite, acardite, and diphenylamine, as aell as powder samples containing ethyl centralite; comparison analyses were also made by one or both of the standard procedures mentioned above. The results of these experiments are presented in Tables I and 11. Additional experiments, the results of which are not given in the tables, demonstrated that acetic acid is virtually inert toward bromination under conditions of the procedure and that the presence of either nitroglycerin or diethyl phthalate does not introduce serious error into the estimation of centralite. The data in Tables I and I1 demonstrate that this volumetric procedure ‘involving bromination in acetic acid solution is satisfactorily accurate and precise, and that the results are not critically dependent on the time allowed for bromination. As it is more convenient to carry out than the carbon tetrachloride and alcohol procedures, it is recommended for the estimation of stabilizers in smokeless powders. ACKNOWLEDGMENTS
The authors wish to express their thanks to W. A. Schroeder and James G. Renno for carrying out experiments on the aberrations due to ether peroxides, and David P. Shoemaker for assistance in preparing the manuscript. LITERATURE CITED
(1) Ellington, 0. C., and Beard, H. G., J . SOC.Chem. Ind., 50, l5lT (1931). ( 2 ) Levenson, H., IND. ENG.CHEW,ANAL.ED., 2,246 (1930). (3) Swift, E. H., “System of Chemical Analysis”, pp. 71, 77, New York, Prentice-Hall, 1940.
CONTRIBUTION 1056 from Gates and Crellin Laboratories of Chemistry, California. Institute of Technology. Based on work done for t h e Office of Scientific Research and Development under Contract OEMsr-881 wlth the California Institute of Technology.
