Between cy-PbO?, Few04 (Wolframite), and FeNb06 (Columbite) and the Polymorphism of FeNbO4," Schweis. Mineral. Petrog. l6 H. Schrocke; personal communication, 1964. K. Brandt, "X-Kay Studies 011 ABO4 Compounds of Rutile Type and AB206 Compounds of Columbite Type," Arkiv Kemi, Mineral. Geol., 17A [15] 1-8 (1943). Helmut Schrocke, "Heterotype Miscibility Between Wolframite and the Rutile Group," Beitr. Mineral. Petrog., 8,339-48 (1962). lo R. S. Roth and J. L. Waring, "Ixiolite and Other Polymorphic Types of FeNbO4," A m . Mineralogist, 49 [3-41 242-46 (19641. Milt., 43 [l] 217-31 (1963). ramite and the Columbite Group," Beitr. Mineral. Petrog., 8, 92-110 (1961).' 2o L. S. Darken and R. W. Gurry, "The System Iron-Oxygen: 11," J. Am. Chem. Soc., 68 [5] 798-816 (1946).

Since lattice energy calculations have indicated that the most stable sulfides of the periodic system could be expected in the neighborhood of the elements of the rare earth and actinide series, a thorough study of the sulfides of typical representatives of these elements was made. This paper describes the results of the study of the sulfides of thorium and uranium.The earliest careful study of thorium and uranium sulfides is that of Picon4r6sB who studied methods of preparation of ThS2 and US2 and the properties and reactions of these compounds. Strotzer and Zumbusch7 and Strotzer, Schneider and Biltz8 extended the study to polysulfides above the MS2 compounds and to oxidation states below the four plus state. However, due to very extensive oxygen contamination during preparation, the compositions and composition ranges given for the various phases below MS2 were greatly in error.In the present work both uranium and thorium were found to have compounds of the 2f oxidation state, US and ThS, which have the NaCl crystal structure. No compounds below the 2+ oxidation state were found. The solid solution ranges for these compounds appear to be relatively small. The next phase found above the MS phase was a M& phase corresponding to the 3f oxidation state. Both U2S3 and Th&s were found to have the same orthorhombic structure with apparently relatively small solid solution ranges. Th83 is an unusual thorium compound as i t is the only definitely established compound observed to date which contains thorium in the 3+ oxidation state. ThSz prepared by conversion of the oxide by H2S in a graphite container had the orthorhombic PbCt structure. US2 was prepared in a similar manner. Upon heating under reduced pressures, both lost sulfur through a solid solution range. US2 was less stable than ThSz and lost sulfur a t lower temperatures. A compound, Th&, of hexagonal structure, has been prepared by heating liquid ThS2 above 1950' under reduced pressures. It has a homogeneity range of approximately ThS1.71--1.,6. Because of the ready loss of sulfur, the study of the uranium sulfide range down (1) This work was performed under Manhattan District Contract to a composition corresponding to Th&2 did not give definite results. Experimental I. Preparation of the Sulfides of Uranium and Thorium.-Four different methods of preparation will be described below. The first three methods were also used for the preparation of the cerium sulfides and the apparatus used and details of the procedures may be obtained from the paper by Eastman, Brewer, Bromley, Gilles and Lofgreno on the cerium sulfides.Method 1.-This method is suited only for ThS2 and US2 since it involves the treatment of the oxides with excess H2S in a carbon system. Thus one obtains the highest sulfide stable at the temperature of the preparation. The temperature of the reaction should be varied between 1200-1300°; the rate of reaction a t these temperatures is fairly rapid. During the course of the reaction, the oxysulfides ThOS and UOS are first formed at lower temperature ...

Chikalla Reply 309HE vapor-pressure ratios in Table I11 were calculated in 1959 using the data of Ackermann et al.' for UOZ and the data of T Phipps et a1.2 for Pu02. This was the only source of volatility data for PuO2 at that time. In checking the original work an error in slope was found on the extrapolation plot used, which thus gave rise to the ratios reported. The writer agrees with the ratios tabulated by Mr. Gross and wishes to thank him for this correction.

The heat of sublimation of graphite and the heats of dissociation of CO and C2, which have been the subject of much controversy in recent years, have been unambiguously established by the direct determination of the total vapor pressure of graphite by an equilibrium effusion method and by the determination of the partial pressure of C2(gas) in equilibrium with graphite. The heat of sublimation of graphite to C(g) is found to be ΔH0=170.39±0.20 kilocalories per mole at 0°K. The heat of sublimation of graphite to C2(g) is found to be ΔH0=233.1±7 kilocalories per mole. The heats of dissociation of C2 and CO have been shown to be 4.7±0.3 and 11.109±0.01 electron volts, respectively. The accommodation coefficient of carbon gas on graphite at high temperatures is found to be about 0.3 and vaporized carbon gas is shown to be in the 3P ground electronic state.

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Crucibles have been prepared from all af the sulfides of barium, cerium, and thorium, and also from some of the mixed sulfides of cerium with thorium and uranium with thorium. The type of molds used, as well as the methods of pressing of the sulfide powders, are described in detail. Sintering procedures and techniques are listed for each of the various refractories. More than 800 refractory sulfide crucibles have been produced by the authors in the Berkeley laboratories. These crucibles have ranged from extremely small containers with 0.0026 cc. capacity to crucibles with 50 cc. capacity. Tests of these crucibles indicate that they are satisfactory refractories for a large number of metals and halides. Tests of the individual sulfide refractories as containers for various melts are summarized. The individual differences, as well as similarities, of the sulfide refractories are pointed out.

The vaporization behavior of the boron-sulfur system has been studied mass spectrometrically with a glassy, sulfur-rich B2S3 sample, a stoichiometric B2S3 sample, a stoichiometric B2S3 -Zn mixture, and a FeS-B-Zn mixture. Glassy B& gave the most intense and most complicated spectra; the stoichiometric BsS3 sample, the stoichiometric B2S3-Zn mixture, and the early stages of the FeS-B-Zn mixture gave, in the temperature range 400-650 O, indistinguishable spectra that were intermediate in intensity and complexity; and the ZnS-B system, to which the FeS-B-Zn mixture converted in later stages, gave the simplest spectra with the lowest intensities. Ion intensities, appearance potentials, metastable transitions, fragmentation patterns, and temperature dependences are used to show that the parent ions from stoichiometric BZS3 were polymers of B2S3(g) and that BZS3(s) vaporizes congruently. Sulfur-rich samples vaporize incongruently to give polymers of both BSz(g) and BzS3(g). Sulfurdeficient systems also give B2S2(g). Polysulfide bonds are suggested as the cause of the higher volatility and lower melting points of the sulfur-rich samples.he discovery of the gaseous ions of polymeric com-

Two experiments of the successive vaporization type, five mass spectrometric vaporization experiments, and two isomolecular exchange reaction experiments were undertaken to resolve discrepancies in the thermodynamics of the titanium—oxygen system. The first two types of experiments confirmed that Ti3O5(s) is the congruently vaporizing phase. The second type of experiment showed that the principal reaction accounting for the congruent vaporization is Ti3O5(S)=TiO(g)+2TiO2(g). In the third type of experiment, measurements on the isomolecular exchange reaction TiO(g)+Sc(g)=Ti(g)+ScO(g) showed that the dissociation energy of TiO(g) is smaller than that for ScO(g) and on the basis that D0o(ScO) is 160.4±2.0 kcal/mole, D0o(TiO) becomes 156.9±2.2 kcal/mole, or 6.80±0.10 eV. This result may be combined with earlier vapor pressure measurements on Ti3O5(s) and the congruency condition to yield D0o(TiO2)=311.7±1.8 kcal/mole, 13.52±0.08 eV, or very nearly twice D0o(TiO). One of the two previously discussed discrepancies in the thermodynamics of the titanium oxides appears to have been resolved, and the likely resolution of the other is discussed.