aominal operating current for 12AY7 and should be optimal for long tube life. LITERATURE CITED
(1) Babcock, W. E., EZectronics31, No. 37, 90-3 (1958). (2) Blumer, Max, A x a . CHEM. 32, 772 (19GO).
(3) Whitlock, w.1 "Techniques for A lieation Of Tubes in d g b a r y Equipment Wright Air Development Center Technical R ~ 55-1, 1-21 (October 1955).
SIR: We wish to thank C. $1. Proctor for his comments and suggest modifica~tion~ of . the circuit according to his recommendations.
MAXBLUMER CHARLES M.PROCTOR Wooda Hole Oceanographic Institution 2540 122nd Ave., S. E. Woods Hole, Mass. Bellevue, Wash.
imolybde nu m Ca rbi R. J.
FRIES and CHARLES P. KEMPTER 10s Alamos Scientific Laboratory, University of California, 10s Alamos, N. M.
HE crystal structure of Mo2C was T f i r s t determined by Westgren and Phragm6n (6),who reported a closepacked hexagonal lattice. The most recently published lattice constants were reported by Kuo and Hagg (2) to be a = 3.002 A. and c = 4.724 A. Lander and Germer (3) have found evidence of a face-centered cubic modification of MOZCwith a = 4.15 A. Nadler and Rempter (4) found the melting point of MozC to be 2410' ct 15' C. The starting material used for this investigation was Fansteel Metallurgical Corp. MozC. I n order to reduce the amount of free carbon and combined nitrogen and oxygen present in this material, a 12-gram sample of the powder was pressed at 50 tons per square inch in a 1/2-inch pellet die and heated inductively a t 1950' C. for 90 minutes in a helium atmosphere. The pellet wae placed on a small MotC tablet, which in turn was supported by a graphite pedestal. This heated sample analyzed 93232% Mo, 6.66% total carbon, 30 p.p.m. nitrogen, and 195 p.p.m. oxygen (1). Free carbon was not detectable. This analysis
corresponds to a stoichiometry of pvl[o*.o*c. The spectrographic analysis results (based on MOO^) are shown in Table I.
Table II.
X-Ray Powder Diffraction Data for M o K
Miller Indicee
Relative Intensity
100
30
002 101 102 110 103 200 112 20 1 004 202 104 203 120 121 114
122
30
100 40
50 70 10
eo eo
10 20 20 60
20 95 95 70
d, A. 2.59 2.357 2.271
+
proportional to 4 tan 4, where is the complement of the Bragg angle. The back-reflection lattice constants obtained were a, = 3.00281 =t0.00007 A. and c, = 4.72878 i 0.00014 A,, uncorrected for refraction. The standard deviations are of courE a measure of the precision, not the accuracy of the determinations. Correcting for refraction, one obtains a, = 3.00292 A,, co = 4.72895 A, and c,/a, = 1.575. Therefore, t8hevolume of the hexagonal and the theounit cell is 36.929 cu. 9. retical density (for one MozC per unit cell) is 9.167 grams per cc. at 25' C.
1.745
1.500 1.347 1,298 1.266 1.253 1.182 1.139 1.076 1.003 0.9829 0.9622 0.9288
0 9076
ACKNOWLEDGMENT
The authors thank 0. R. Simi for the spectrographic analysis, G. C. Heasley, R. D. Gardner, and Lois F. Gritzo for the chemical analyses, L. -4.Wahman for the x-ray film reading, and Dorothy L. Cooper for the I B M 704 work.
I
LITERATURE CITED
(1) Kriege, 0. H., Los Alamos scientific
Table I. Spectrographic Analysis of
Major 300
