50 Rogers — Eglestonite from, San Mateo County, Gal. 



is soluble on heating. The mineral is blackened by ammonia, 

 and slightly darkened by hydrogen sulphide solution. Qualita- 

 tive tests show the presence of mercury and chlorine and the 

 absence of the sulphate radical. 



Quantitative analysis. — In order to make the identification 

 of the mineral eglestonite more certain, a quantitative analysis 

 was made by the writer. The powdered mineral mixed with 

 ignited lime free from water and chlorine was heated in a hard 

 glass tube. The tube with the mercury sublimate was weighed, 

 and then weighed again after driving off the mercury. The 

 loss is mercury. The residue was dissolved in nitric acid and 

 the chlorine determined by precipitating AgCl. The results 

 obtained with 25 mg. of carefully picked, almost pure, mineral 

 are as follows : 



Atomic Calculated for 



Analysis ratio Hg 4 Cl 2 



Hg... 88-00 2-10 90-21 



CI 7-43.. 1-00 7-99 



The theoretical percentages for Hg 4 Cl 2 0, the formula estab- 

 lished by Hillebrand,* are given in the last column. These 

 quantitative results also agree with the calculated percentages 

 for kleinite and terlinguaite, but considering the small amount 

 of material and the slight impurities the agreement with egles- 

 tonite is as good as can be expected. 



Identity with eglestonite. — The qualitative and quantitative 

 tests prove that the mineral is an oxychloride of mercury, with 

 a formula at least near that of eglestonite. The isometric char- 

 acter of the crystals limits the mineral to eglestonite or moses- 

 ite.f The habit of the crystals, the absence of twinning, the 

 normal isotropic character, the darkening on exposure to light, 

 and the absence of the sulphate radical, all taken together 

 make it certain that the mineral is eglestonite. 



Stanford University, Cal., 

 April, 1911. 



* Journal of the Am. Chem. Soc, vol. xxix, p. 1193, 1907. 



f Canfield, Hillebrand, and Schiller, this Journal, vol. xxx, pp. 202-8, 1910. 



