106 REPORTS ON INVESTIGATIONS AND PROJECTS. 



ditions which protected the molten mass from oxidation. The hypothesis is 

 advanced that the loess formation was intruded by igneous masses which 

 melted down the adjacent loess and formed the present black scoriae. The 

 lack of oxidation of the scoriae and their abundance in the field precludes 

 the possibility that they were formed by the melting down of loess by bon- 

 fires or any type of fire in the open air. Prehistoric man is, therefore, not 

 responsible for their occurrence. 



(18) The expansion coefficient of graphite. Arthur L. Day and Robert B. Sosman. 



Jour. Wash. Acad. Sci., 2, 284-289. 1912. 



A preliminary publication of the results of the investigation reviewed be- 

 low (No. 19). 



(19) The expansion coefficient of graphite. Arthur L. Day and Robert B. Sosman. 



J. Ind. Eng. Chem., 4, 490-493- 1912. 



The expansion of artificial graphite up to 1500 was determined as a basis 

 for the measurement of specific volumes of minerals and rocks at high tem- 

 peratures. Two methods were used : ( 1 ) the expansion of a bar of graphite 

 self-heated by a heavy current was measured by means of micrometer micro- 

 scopes at a fixed distance apart; (2) the expansion of the same bar was ob- 

 served in a platinum-resistance furnace. The mean coefficient from zero 

 degrees is 0.55 -f- 0.0016 t. 



The comparison of this value with other determinations on natural graph- 

 ites and other forms of carbon shows a parallelism between the temperature 

 of formation and the smallness of the coefficient, and indicates that the name 

 "graphite" covers a continuous series of substances of varying properties. 



(20) The sulphides of zinc, cadmium, and mercury; their crystalline forms and genetic 



conditions. E. T. Allen and J. L. Crenshaw. Microscopic study by H. E. 

 Merwin. Amer. Jour. Sci., 4, 34, 34 I_ 396- 



The sulphides of zinc are enantiotropic, with an inversion point at 1020 . 

 Sphalerite is the stable form below this temperature, wurtzite above. Their 

 indices of refraction, dispersion, and specific gravities were determined. Iron 

 in the form of ferrous sulphide is present in solid solution in the ferruginous 

 sphalerites, since the specific volume, index of refraction, and inversion-point 

 change continuously with increasing percentage of iron. Sphalerite was 

 formed synthetically by action of alkali sulphides on zinc salts at 200 and 

 above. Wurtzite was obtained by action of hydrogen sulphide on solutions 

 of zinc salts containing free acid at temperatures between 250 and 350 . 



Only one crystalline form of cadmium sulphide was obtained. It is iden- 

 tical with the mineral greenockite. Crystallographic and optical measure- 

 ments and determinations of specific gravity were made on a very pure 

 synthetic preparation. 



Besides cinnabar, a black sulphide of mercury, probably identical with 

 metacinnabar, and a new form, hexagonal, but with properties distinct from 

 cinnabar, were obtained. Cinnabar is the stable form ; the other two are 

 monotropic forms. 



The most interesting result for geochemistry which was obtained in these 

 synthetic studies was the following: The unstable crystalline forms, meta- 

 cinnabar, wurtzite, and marcasite, are obtained only from acid solutions, 

 while the corresponding stable forms, cinnabar, sphalerite, and pyrite, are 

 the only product of alkaline solutions, though they may be obtained from 

 acid solutions also. 



