ANALYTICAL CHEMISTRY
290 Table VI.
Analysis of Crude Benzene Hexachlorides F?
Crude
12.7.12.8 14.0,14.&13.7 17.0,17.0,17.6,16.9 11.2,11.4,11.8,11.8,11.4
12.9.12.9 16.2,16.4,16.0
SUMMARY
A mass isotope dilution method has been developed for absolute determination of the gamma isomer and, in principle, for some of the other known isomers of benzene hexachloride in crude benzene chlorination products. I n particular, the use of infrared spectrophotometry as a means of determining the extent of the mass isotope dilution has been described and its extension as a general absolute assay technique for the analysis of many different kinds of substances under a wide variety of conditions visualized. I n general, it would appear much easier to introduce deuterium into an organic molecule as a marking atom than practically any other kind of atom, the more so if the organic molecule in question cannot be svnthesized by other than natural methods, for hydrogen exchange is of far more common occurrence and more easily achieved under sufficiently mild conditions than is true for other kinds of atoms. Because the introduction of deuterium into a molecule results, in general, in rather extensive changes in its infrared spectrum, it should always be possible to determine the extent of the deuterium isotope dilution by such means. Even under the most unfavorable conditions where other changes in the infrared spectrum are only trivial the presence of the C-D linear stretching vibration a t about 4.5 mu, a region not generally interfered with by other types of vibrations, Tyould provide a means of analysis. Moreover, for compounds whose solubility properties preclude the use of any otherwise usable solvent, one can use solids equally effectively (1, 13). Thus the combined general methods employed in this paper are of considerable scope and interest from the point of view of the absolute analysis of organic substances occurring in complex media. The use of the concept of isotope dilution in analysis is not new (15), but the specific use of infrared spectrophotometry in determining the mass isotope dilution in place of the older and more cumbersome
combustion-density of water methods is believed to be substantially original (14). Because impurities are Jvithout effect upon the accuracy of this method, its reliability is limited only by its precision, which is constant over practically the whole range of concentrations, and moreover, as the precision would appear necessarily superior to that attainable by direct infrared analysis, the isotope dilution method must take precedence over it and all other methods as a primary assay by n-hich the reliability of other methods may be gaged. ACKNOWLEDGMENT
The authors wish to express their thanks to Gustav Stein and
R. Valerio of the hferck Development Laboratories for having carried out the photochlorination of the hexadeuterobenzene, and for having separated and purified the individual deutero and protio isomers used in this investigation. LITERATURE CITED
(1) Barnes, R. B , Gore, R. C., Williams, E. F., Linsley, S. G., and Petersen, E. M., IND.ENG.CHmI., SNAL ED.,19,620 (1947). (2) Bowen, C. V.,private communication. (3) Bowman, P. I., Benedict, W. S., and Taylor, H. S., J . Am. Chcm. Soc., 57,960 (1936). (4) Daasch, L. W., IND.ENG.CHEM.,ANAL.ED., 19,779 (1947). ( 5 ) Heal, R.E., and Dunn, H. 8.,forthcoming publication. (6) Herrfeld, N., Ingold, C. K., and Poole, H. G., J . Chem. Soc , 1946,326. (7) Ingold, C. K., Raisen, C. G., and Wilson, C. L., Ihid.. 1936,915. ( 8 ) Kauer, K. C., Du Vall, R. S., and Alquist, F. N., Abstracts of Papers, 110th Meeting AM. CHEM.SOC.,p. 52 I, 1946; I n d . Eng. Chcm., 39,1335 (1947). (9) Kauer, K. C.,Du Vall, R. B., and Alquist, F. N., Ihid., 39,1336 (1947). (10) Oetjen, R. A., Kao, C.-L , and Randall, H. M., Rev. Sci. Instruments, 13,515 (1942). (11) Rosenblum, C.,private communication. (12) Slade, R. E., Chemistrv & Industry, 64,314 (1945). (13) Trenner, N.R., and Walker, R. W., forthcoming publication. (14) Walcher, W., Ergeh. Ezakt. Naturw., 18,155 (1939). (15) Weissberger, A., “Physical Methods of Organic Chemistry.” 1’01. 11, p. 1296,New York, Interscience Publishers, 1946. (16) Weldon, L. H.P., and Wilson, C. L., J . Chem. SOC.,1946,237. RECEIVED June 12, 1948. Presented before the Division of Analytical and Micro Chemistry a t the 113th Meeting of the h~rsaxcasCHEMICAL SoCIETY, Chicago, Ill.
A Flowmeter for High Temperature Gases E. W. COMINGS AND R. C. JOHNSON’ University of Illinois, Urbana, I l l .
T
HE development and specification of pyrotechnic fuel mixtures during World War I1 gave rise to the need for a simple
but fairly accurate method of measuring the instantaneous volume rate of gas evolved ( 2 ) . The required apparatus consists essentially of a sharp-edged orifice fitted nith a shielded thermocouple in a high velocity gas stream to permit the simultaneous measurement of hot gas temperature and pressure across the orifice. A baffle \vas provided to prevent the thermocouple from “seeing” the incandescent surface of the pyrotechnic mixture. This device came to be known as a volume tester.
The fuel is ignited and temperature and pressure readings are taken a t frequent intervals throughout the burning time.
APPARATUS
The device was constructed in several sizes. a cross section through a typical unit. 1
The gas from the surface of the pyrotechnic mixture flows around the baffle plate and through the tube containing the thermocouple. This tube serves the dual purpose of imparting a relatively high velocity to the gas floviing by the thermocouple and of shielding the latter from the cooler sides of the apparatus. The gases then exhaust through the orifice to the atmosphere. A pressure connection is provided in the side of the unit near the orifice, which is connected to a manometer or pressure gage. Chromel-alumel B. and S.gage 22 thermocouple wires were found satisfactory with gas temperatures approaching 2000 O t F . All except the junction was coated with Sauereisen for protection. The calibration of the couple yas checked a t a known temperature after each one to three tests.
Figure 1 shows
Present address, Pennsylvania State College, State College, Pa.
CALCULATIOKS
The relationship between pressure drop across the orifice and the weight rate of flow is given by the Equation (1, 3 )
V O L U M E 21, N O , 2, F E B R U A R Y 1 9 4 9
29 1
A method of measuring the flow of hot gases from a pyrotechnic fuel mixture is described. The gases pass over a shielded thermocouple and are then exhausted through a sharp-edged orifice. The flow rate is corrected for gradual changes in gas temperature and pressure. The device is termed a volume tester.
8M ORIFICE M , S H A RIP EDGED N y STAINLESS STEEL PLATE
T$ 1 11
q
e=
1
pa
520 pi 14.7 X 144 X Ti 1c
Ps
=
PRESSURE TAP
,I1 -
379
(3)
2 2 B * S CAGE CHROMEL ALUMEL THERMOCOUPL
BAFFLE P L A T E H E L D BY FOUR STEEL STRIPS
IGNITER INLET I
When the burning rate is not constant and causes variations in the flow of gas during the test, a plot of q , against time niay he integrated graphically to give the total volume of gases generatcd, reduced t o standard conditions. From the equation
IV
A T H OF I.
= Pep8 = q,
Ai
-
379
I
the total weight of gas is determined and compared Kith the Keight of the pyrotechic mixture to obtain a material balance. 12.5 IN.
..I Figure 1. Volume Tester for Measuring Instantaneous Hot Gas Flow Rates
where
TIME,MINUTES
Figure 2.
Equation 1 is accurate within 1% for palp, not less than 0.8 and the error is not serious when p,/p1 approaches 0.5. For a 0.41 0.35 B4 given unit and gas = K , a constant. The ink stantaneous volumetric rate of flow in terms of volume reduced to standard conditions (60" F. and 1 atmosphere in this paper) is given by
+
PI = W/P.
The perfect gas law may be used.
Relation of Gas Temperature and Pressure Difference across Orifice t o Time
Similarly the instantaneous volumetric rate in terms of actual volume a t the temperature and pressure in the unit is given by the equation q1
= W/Pl
For two gases of different average molecular n-eight, M a and of k , each flowing through the orifice under identical conditions of temperature and pressure, the ratio of their volume flow rates (either actual or reduced t o standard conditions) is
M a , but with the same value
292
ANALYTICAL CHEMISTRY
This makes it possible to calculate the rates of flow on the basis of an assumed molecular weight and later to correct these when the true molecular weight is determined by gas analysis. From equation 2
d?:
d” ,-
I-
q, = c‘y
= c y
d/ap
Pa
and from Equation 4
and k. These lines may be constructed for a reference gas, such as air. The values of q. read from these curves may be integrated over the period of time covered by the test and the total gas volume obtained in terms of this reference gas. Equation 5 will then serve to convert the integrated flow of reference gas to the flow of actual test gas. The application of continuously recording temperature and pressure difference instruments to the procedure will be selfevident. The method may also be applied to other orifice in stallations for measuring gas flow.
(7)
I
0.25
ACKNOWLEDGMENT
This paper is based on work done a t the Munitions Develop ment Laboratory a t the University of Illinois during World War 11. E. D. Shippee contributed to the project.
ACTUAL CAS FLOW RATE,qi
\
=
c”
= c’
VI
4
520 379 = 9.64 c’ 14.7 X 144
= c’ 4 3 7 9 X 14.7 X 144 =
0
39.3 c,
520
TIME, MINUTES
Figure 3.
orifice constant; a value of 0.61 wm used
c
Relation of Gas Flow Rates to Time
DO D1
= orifice diameter, feet
go
=
K
= 0‘41 +:’35
k
=!?
Gas volumes measured under actual conditions of temperature and pressure and also at 60’ F. and 1 atmosphere
The steps in making the calculations may be summarized as follows: 1. Temperatures and pressures ( A p ) are tabulated for a number of time intervals. 2. The values of pl (barometric pressure + A p ) are calculated.
(
it;:)
3. The values of = and y are determined. 4. The instantaneous values of qa and q1 based on average values of molecular weight and k are obtained from Eauations 6 and 7. 5. The flow rates, q., are then plotted against time and integrated graphically to obtain the total volume of gas (corrected to standard conditions) emitted during the test period. 6. This value is corrected for molecular weight when necessary, converted to total mass, and used in a material balance as a check on the validity of the measured flow rates. I
The mpthod has consistently given material balances which check within * 5 % . I t is felt that this is reasonable accuracy in view of the high temperatures and varying flow rates encountered. Typical curves of pressure and temperatue versus time and the calculated curves of actual volume rate and volume rate correrted to standard conditions are shown in Figures 2 and 3. When used as a standard test procelure the calculations may be simplified by preparing suitable graphs and a nomograph. In step 3 a nomograph is useful for calculating p l / p a from the measured values of p l and TI. In step 4 a series of lines a t constant p i / p , of either q1 or qs as ordinate against A p as abscissa on log-log paper may be prepared for constant barometric pressure
= diameter upstream from the orifice, feet
32.17 lb. (mass) X feet Ib. (force) X sec?
B4,a constant for a given unit and gas
ratio of specific heat a t constant pressure to sljecific
CV’
M
pl
heat a t constant volume = molecular weight of gas = absolute pressure upstream from the orifice, pounds
(force) per square foot Ap = pl - p z , difference in pressure across orifice q1 = volumetric rate of flow measured a t the temperature and pressure upstream from the orifice, cubic feet per second q. = volumetric rate of flow measured a t 60” F. and 14.7 pounds per square inch absolute pressure So = cross-sectional area of orifice, square feet T I = absolute temperature upstream from orifice, degrees Rankine W = mass rate of f l o ~pounds , (mass) per second
’a (0.41 + 0.35 B4)
y
= correction factor, 1 -
pl
= gas density, upstream from orifice, pounds per cubic foot = gas density at 60” F. and 14.7 pounds per square inch
pn
Plk
absolute, poulzds per cubic foot
LITERATURE CITED
(1) Am. SOC.Mech Engrs., “Fluid Meters, Their Theory and Application,” 4th ed., Part 1,p. 107, 1937. (2) Comings, E. W., Adams, C. H., and Shippee, E. D., 2nd. Eng Chem., 40, 74 (1948). (3) Walker, W. H., Lewis, W.K., McAdams, W. H., and Gilliland.
E. R., “Principles of Chemical Engineering,” 3rd ed., p. 66. New York. MoGraw-Hill Book Co., 1937. RECEIVED April 26.1948.
