114 abstracts: geochemistry 



can not be regarded as good evidence for the occurrence of any trans- 

 formation or chemical reaction, whether produced by subjecting the 

 system to compression or by other means. J. J. and L. H. A. 



PHYSICS. — Mixtures of amorphous sulfur and selenium as immersion 

 media for the determination of high refractive indices with the micro- 

 scope. H, E. Merwin and E. S. Larsen. American Journal of 

 Science, 34: 42^7. 1912. 

 Fused mixtures of sulfur and selenium are glassy when cold. By 

 standardizing the mixtures with respect to their refractive indices by 

 measurements on prisms molded into the angle between glass plates, 

 they can be used to match the refractive indices of suitable substances 

 immersed in them and studied under the microscope. A chart showing 

 the refractive indices of various mixtures for several wave-lengths has 

 been prepared, and a method of interpolating values of refractive 

 indiqps, obtained by using a monochromatic illuminator, explained 



H.E. M. 



GEOCHEMISTRY. — The sulfides of zinc, cadmium, and mercury; their 

 crystalline forms and genetic conditions. E. T. Allen and J. L. 

 Crenshaw. Microscopic study by H. E. Merwin. American 

 Journal of Science, 34: 341-396. 1912. 



The sulfides of zinc are enantiotropic, with an inversion point at 

 1020°. Sphalerite is the stable form below this temperature, wurt- 

 zite above. Their indices of refraction, dispersion, and specific gravities 

 were determined. Iron in the form of ferrous sulfide 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 sulfides on zinc salts at 200° and above. Wurtzite was obtained 

 by action of hydrogen sulfide on solutions of zinc salts containing free 

 acid at temperatures between 250° and 350°. 



Only one crystalline form of cadmium sulfide was obtained. It is 

 identical with the mineral greenockite. Crystallographic and optical 

 measurements and determinations of specific gravity were made on a 

 very pure synthetic preparation. 



Besides cinnabar, a black sulfide 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. 



