TEST OF PROCEDURE
The procedure described was applied to a variety of phosphates from several sources and with a range of fluoride content from 0.06 to 4.2y0 fluorine. These previously anby the s. Survey with the distillation technique during the course of several years, and also those National Bureau of Standards
189.
standard phosphates which were available. The results in the table were selected from a larger set of data to illustrate the degree of accuracy a t low, and medium levels Of fluorine* The Bureau of Standards standard sample No. 120 phosphate rock was used as the reference standard. (This s h n d ard has been discontinued.) The standard sample currently available is y o . 56b, for which only one determination is cited by the Bureau of Standards.
LITERATURE CITED
(1) Fox, J. E., Jackson, IT. A., ANAL. CHEM.31,1657 (1959). (2) Parkerj 2 4 . jG o d d a d . 4.p.1 Anal. Cham. Acta 4,517 (1950).
c.
(3) Shapiro, L., Brannock, IV. I\7., U. S. Geol. Survey, Bull. 1036-C (1956).
LEONARD SHAPIRO
U.S.Geological Survey Washington, D. C.
authorized by the Director, U. S.Geological Survey.
PUBLICATION
Zirconium Carbide
CHARLES P. KEMPTER and R. JAY FRIES
Los Alamos Scientific Laboratory, University of California, Los Alamos, N. M. of zirconium T carbide was first reported by van Arkel ( I ) . The space group is 0; HE CRYSTAL STRUCTURE
F m 3m (NaC1 structure-type) with 4 (ZrC) per unit cell. The x-ray powder data file contains one "ZrC?" data card (1-1050) which lists approximate interplanar spacings with no Miller indices assigned. The starting material used for this investigation was high purity ZrC obtained from Union Carbide Metals Co. About 10 grams of this material were pressed in a pellet die at 25 p.s.i. to form a cylindrical sample 0.5 inch in diameter and 0.75 inch long. The sample was then set in a graphite crucible and heated inductively in 1 atm. of helium. The sample was heated slowly to about 28OO0C.,soaked a t this temperature for 1 hour, and then cooled rapidly in helium. Before this treatment, the material analyzed 87.9% Zr Hf, 0.9% free C, and
