V O L U M E 22, NO. 7, J U L Y 1 9 5 0 high. The addition of gum arabic in the back-titration with thiocyanate made the end point sharper and more distinct. LITERATURE CITED
(1) KolthoK. I. M., and Stenger. V. A., "Volumetric Analysis." Vol. I,p. 193, New York, Interscience Publishers, 1942.
953 (2) Lottermmer. A., End Lorens, W..Kolloid Z., 68, 201 (1934). (3) Pierce. W. W., and Haenisch, E. L., "Qusntitative Analysis," 5 ed., B. 299, New York, John Wiley & Sons,1948. (4) Schneider. L., J . Am. Chern. Soc.. 40,591 (1918). Rmcmmio July 29.1949.
Photometric Method for Estimation of Minute Amounts of Mercury Use of G.E. Germicidal Ultraviolet Intensity Meter C. W. ZUEHLKE AND A. E. BALLARD Eastman Kodak Company, Rochester, N. Y.
Micragroms of Mercury
Figure 2
'
Figure 1. Apparatus w i t h Lamp Housing Removed
N A prevlous article ( 1 ) a procedure was given for the determination'of 0.02 to 0.6 miorogram of mercury in up to 500 ml.
of solution. The method consists in collecting the mercury, v o l e tilizing it into a quartz-ended cell, and measuring the amount of light of 2537 A. ahsorbed by the mercury vapor, using a specially designed ultraviolet photometer. Recently, the General Electric germicidal ultraviolet intensity meter has been offered &s a completely self-contained unit, having dimensions of 6 X 5 X 4 inches (15 X 12.5 x 10 om.). A study of the reproducibility and sensitivity of this instrument pdicatea that the substitution of this meter for the special photometer origindly used makes possible the assembly of k compact and comparatively inexpensive apparatus. This should extend the use of the procedure considerably!, I Figure 1 is a photograph of the apparatus with the lamp housing removed. A is the 4-watt G.E. germicidal lamp, B is the shutter, C i s the quartz-ended sample cell, D ia the movable furnace, and E is the meter. A 350-ohm rheostat for varvine the intensity of the germicidal lamp and the rheostat for co6trdliug the furnace temperature me not shown. OPERATION O F METER
The germicidal lamp is turned on and allowed to operate a t full line voltage for 10 minutes with the shutter closed. The meter circuit is balanced a t zero in artificial light (in an inside
Microgromr of Mercury
Figure3
d
ANALYTICAL CHEMISTRY
934
room),, which is a standardization of the meter circuit. The meter IR Bet for the range from 0 to 100 mw. per square foot, the shutter i8 oDened.. and the lieht intensitv is adiusted bv means
known amounts of mercury in 250 ml. of water through the complete procedure. ACKNOWLEDGMENT
Thanks are here extended to Warren Ksmm and Howard MoKinney for assembling the apparatus and preparing the curves. pa.d--!iaidinf? I r k pleated by mean8 of'tbe movablefurnace, and
LITERATURE ClTED
(1) Ballard and Thornton, IND.ENO.C~EM., ANAL. ED., 13, 893
(1941).
The
CI'PVCS
given in. Piqures 2 and 3 were obtained by taking
RECEIVED January 16, 1950. Communication 1310 from the Kodsk Research Laboratories.
32* B.BX (Cyc1otsi.methylenetrinitrarnine) Contr5,loixtsrl 5 y ?VA?,TE!$ C MCCROWF, Armour Research Foundation, Illinois Institute of Technology, Chicago 16, 111.
CH,
/\
d 2 25 2 20 2 12 2 08
I/Il Very weak Very weak 0 04 0 04
-
I/Ii 0.07
d 2.01 1.97 1.92 1.86
0.09 Very weak 0.07
.
Structural Fornula for RDX
DX is the symbol for the high explosive cyclotrimethylenetrinitrsmine, which was developed for u ~ eduring World War 11. It can be crystdliaed from a variety of solvents includiiig benzene, nitrometlmne, acetone, acetic acid, and nitric acid. It possesses one very unstable polymorphic form (II), which e m be isohted only in small quantities for a few seconds during fusion studies on a xdcroscope slide. Becmsuse of ita physical instability, there is no possibility of.obtaining RDX I1 even in laboratory recrystallisations.
"-
EDX (1)
CRYSTAL MORPHOLOGY Crystal System. Orthorhombic. Form and Habit. RDX crystallizes in 8 wide variety of habits from needles (nitric acid) and plates (acetic acid) to massive (nitromethane acetone). Usually flattened on 001 showing theforms: (1101, (1201, 11011, {.Olll,md (1111. Axial Ratio. a:b:c = 0.881:1:0.813. Interfacid .Angles (Polar). 1104 110 = 32'50'; 1 2 0 A D O = 590; 101 A io1 = 850 30'; 011 n 011 = 780 20'. X-RAYDIFFRACTTOE DATA Cell Dim~ensions. a. = 11.61. A; h = 13.19 A,; e = 10.72 A. Fomula Wejshts per Cell. 3. Parmula Weight.. 222.13. i3nnsity. ?.?2 (pyoiomster); 1.81 (x-ray).
c
d
Figure 1. Photomicrographsof RDX
