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 ...

E m i s s i o n s p e c t r a offer a useful but relatively unexplored technique I for detection of species in high t e m p e r a t u r e s y s t e m s . In t h i s work the Y \ ' ? .' , ' /'. emission intensity of atomic Th above carbon s~t u r a t e d ThC was used a s a 2 m e a s u r e of Th vapour, p r e s s u r e .by applying the second and t h i r d laws of thermodynamics. A King igraphite t u b e ) ' f u r n a c e operated a t 2100 t o 2500 ".C was. used f o r . t h e e m i s s i o n s o u r c e . The inner b o r e of a graphite h e a t e r tube was coated with p r e r e a c t e d ThC t o .provide a region of equilibrated vapour. 2 ' 1 . Spectra w e r e detected by focusing the vapour e m i s s i o n ontb the ' s l i t of a scanning grating s p e c t r o m e t e r . Intensities w e f e measured. w i t h . a photomultiplier . Intensity m e a s u r e m e n t s w e r e made a t s e v e r a l t e m p e r a t u r e s , . f o r Th e m i s s i o n t o the ground s t a t e a t wavelength:s of 4 4 9 3 . 3 3 and 5760.55A, and fdr the C2 ( 0 -1) band head in t h e Swan s y s t e m a t 5 6 3 5 . 5 A . The second law . . ... of thermodynamics w a s applied to the data by using.the relation p a ,IT.. , Enthalpies of r e a c t i o n obtained w e r e : ' -iii-ThC2 ( s ) = 2C (graph)' ,. v + Th(g); AHo = 165 k c a l . .. . . 298 ThC2 ( s ) = C2 ( g ) + Th(g); = 361 k c a l 2C ( g r a p h ) = C2 (g); AH;98 = 199 kcal. By using, 137.7 . k~a l /~. . a t o m f o r the AH0 of sublimation of Th, the data . 298 . r e s u l t in -26.9* 5 kcal/mole for the AH0 f ,298 of. ThC2. The value for the of sublimation of C2 i s in a g r e e m e n t with previous work and lends confidence .to. the se'cond law t r e a t m e n t . In o r d e r t o use the t h i r d law method a' Th p r e s s u r e calibration was n e c e s s a r y . According1.y a W-foil tube lined on the inside with Th I-~ietal was supported within a graphite heater tube. The e m i s sion intensity was observed a t 1950 "C and c o m p a r e d with the known vapour p r e s s u r e of Th to obtain -" ..the calibration f a c t o r . C o r r e c t i o n s w e r e applied f o r solubility, of W i n .the Th, and f 0 r . a difference in. emitting pathlength of g a s in the two types of U e x p e r i m e n t s . A value of < -24.9 k c a l w a s obtained f o r AH" f ,298 of ThC2. Absolute e r r o r s in the determinations a r e difficult to evaluate. An uncertainty in the stoichiometry of the ThC phase and lack of sufficient 2 heat capacity information complicate the situation. P r e c i s i o n of intensity . m e a s u r e m e n t s i s good, however, with standard deviations ranging f r o m 0.1 t o 67'. . The technique c a n potentially provide rapid and a c c u r a t e determinations of thermodynamic data. It i s well suited for actinide work.in that it i s o l a t e s radioactive m a t e r i a l s f r o m . t h e detection s y s t e m .

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