80 70 60 50 40 9 0 10 20 30 40 50 60 70 80 90 100 2,4Dinitrotoluene, mole %.In a previous note' we reported that we were unable to duplicate the results of Stillwell and Robinson,2 who reported that the alloy commonly known as NarPb contains two formulas of Na31Pb8 in a face-centered cubic unit cell (a0 = 13.27 kX.) and is presumably one of the y-alloys with electron: atom ratio 21 : 13. I n every case our results (on alloy specimens prepared by ourselves) were in agreement with those of Zintl and Harder,a who reported four formulas of NaI6Pb4 in a body-centered cubic unit cell (a0 = 13.29 kx.). We concluded from our results and from some theoretical considerations that the results of Stillwell and Robinson are very probably in error.The alloy studied by Stillwell and Robinson was furnished by Dr. G. Calingaert (then of the Ethyl Corporation, Detroit, Michigan). Recently Dr. Calingaert has furnished us with a specimen of the same alloy prepared in the same way as that furnished to Stillwell and Robinson, and presumably identical to it in regard to structure. We have examined this alloy by powder photography, using the technique ,previously described' except that (1) D. P. Shoemaker, N. E. Weston and J. Rathlev, J . A m . Chsm.(2) C. W. Stillwell and W. K. Robinaon, {bid., 6S, 127 (1933).(3) E. Zintl and A. Harder, 2. physilc. Chem., B84, 238 (1936).
SOC., 77, 4226 (1955).the powdered alloy was sealed in glass capillaries in the dry state rather than in oil. To test the remote possibility that in our previous work a phase transition from the S and R structure to the Z and H structure was brought about by grinding, a photograph was also taken of unground fines screened from the sample. To rule out the existence of the S and R structure at elevated temperatures, an additional powder photograph was taken with the specimen heated at 350" by a blast of hot air. All photographs showed only the Z and H phase, thereby confirming our previous results, and further substantiating the incorrectness of Stillwell and Robinson's results.We wish to thank Dr. Calingaert4 for his kindness in furnishing us wit,h the alloy sample, and the Ethyl Corporation (Baton Rouge, Louisiana) for financial support.In the course of a study of the lubricating properties of phosphates and phosphonates, we measured the vapor pressures of twenty of these and related compounds. Our results fit the Clausius-Clapeyron equation within the accuracy of our measurements. log P (in mm.:of Hg) = -A / T ("K.) + C The vapor pressures were measured from a few tenths of a millimeter up to atmospheric pressure or the thermal decomposition temperature. This is the temperature at which a compound begins to crack and give off more volatile fragments. It is marked by a break in the straight line on a graph of log P vs.
