980EARL W. L~ALMBERG 1701. '76 was made using heat capacity data listed by Kelley.lo The net result is AH298.16 = -488.8 f 0 . 5 kcal.;mole, which is the heat of formation under standard conditions of tantalum pentoxide from the elements. The assigned uncertainty in this instance (and similarly for the other substances in this paper) takes account of uncertainties in the combustion heat of the metal, calibration of the calorimeter, combustion heat of benzoic acid, completion of combustion and correction for impurities in the metal. The mean value for niobium corresponds to -453.44 kcal./mole of niobium pentoxide. The corrections to standard state conditions, made in the same manner as for tantalum, yield Af1298.16 = -455.2 + 0.6 kcal.;'mole as the heat of formation of niobium pentoxide from the elements.The mean value for zirconium is equivalent to -260.82 kcal./mole of zirconium dioxide. Correction to standard conditions results in Af1298.16 = -261.5 =t 0.2 kcal.;mole as the heat of formation of zirconium dioxide.The mean value for tantalum carbide corresponds to -299.17 kcal. for the reaction T a C + 9/rO? = ','?Taz06 + CO? under bomb conditions. Reduction to unit fugacity of oxygen and COZ were made jointly, using a (10) K , I;. Kelley, C. S. Bur. hlines Bull. 477 (i950). suitable modification of i\-ashburn's9 equation ; corrections to a constant-pressure process and to 25' were made as mentioned previously. The result is AH2g816 = -300.0 * 0.5 for the above reaction under standard conditions. Combining with the heats of formation of carbon dioxide6 and 0.5 mole of tantalum pentoxide leads to A H 2 9 8 1 6 = -38.5 * 0.6 kcal./mole as the heat of formation of tantalum carbide from the elements.Previous heat of formation values of tantalum pentoxide, niobium pentoxide and zirconium dioxide were considered in compiling the N. B. S. Tables, the adopted values being, respectively, -499.9, -463.2 and -258.2 kcal./mole. The present work is considered superior in that purer metals were available for study, the use of a kindler (such as paraffin oil) was avoided, and higher precision was obtained. No value for tantalum carbide is given in the E. B. S. Tables.Using entropy values listed by KelleylO and the assumption that the tantalum and niobium oxides have the same entropy of formation, the following free energies of formation are derived : AF0298 16 = -456.5 + 0.6 kcal.imole for tantalum pentoxide, AF0298 16 = -422.9 =t 0.7 kcal./mole for niobium pentoxide, AF0298 16 = -247.7 * 0.2 kcal., mole for zirconium dioxide, and AF29816 = -3S.l =t 0.6 kcal.,'mole for tantalum carbide.
BERKELEY 4, CALIFORXIAA study has been made of the carbonyl compounds which are present in a hydrocarbon-air flame. The experimental methods included formation and chromatographic separation of the 2,4-dinitrophenylhydrazone derivatives. I n addition to the carbonyl compounds which are t o be expected in the light of presently accepted mechanisms, a number of synthesis products mere obtained, compounds in which the length of the carbon chain wa...
