DOLOMITES USED AS FLUXES. 645 



were finely powdered, the other half insoluble. The insoluble chloride might have 

 been contained in apatite crystals combined with calcium. A microscopical examina- 

 tion by Mr. Whitman Cross disclosed, however, no apatite, but a very great number 

 of minute fluid inclusions. Both he and Dr. W. F. Hillebraud were led to believe that 

 the chlorides were contained in tbe inclusions. Dr. Hillebraud partly proved it by 

 levigating the dolomites and thereby extracting nearly three-fourths of the chlorides 

 by treatment with water. Mr. Emmons tlirected me to make experiments on dolomites 

 broken into small pieces, but not powdered. These were digested with water over a 

 water-bath for 48 hours. The first solution contained only traces of chlorides, and the 

 experiment being repeated a second time in the same conditions the second solution 

 did not contain any chlorine, thus proving that the chlorides are not impregnating the 

 mass of the rock, but are contained within the crystals of dolomite. The fact that the 

 Glass-Pendery dolomite, which is half disintegrated, contains much less chloride than 

 the dolomites in compact masses corroborates these views. 



The Dugan and Montgomery dolomites have another point of interest, which 

 should not he overlooked. These dolomites contain traces of sulphides, whether of 

 iron or of calcium there was no time to determine. The fact is, however, that no sul- 

 phide of iron is visible in the microscopical section and that the dolomites treated 

 by weak acids evolve unmistakable sulphureted hydrogen. Should the presence of 

 sulphide of calcium eventually be proved beyond a doubt it would give a great prac- 

 tical value to the observation made by the writer, that carbonate of lime is extremely 

 soluble in sulphide of calcium. This reaction is so striking that it seems j)rob- 

 able that it plays a great part in nature and that carbonates of lime may be carried 

 away in alkaline solutions as well as in acid ones and deposited from these. On the 

 other hand, there seems to be a relation between the quantity of organic matter and 

 the quantity of sulphides contained in the dolomites. The Glass-Pendery dolomite, 

 which contains only traces of organic matter, has no sulphides, while the Mont- 

 gomery dolomite, which contains the largest proportion of organic matter, contains 

 also the largest amount of sulphides. These relations may, however, be purely acci- 

 dental. The dolomites were examined for the jirecious metals, but no silver could be 

 detected in either of them, although it is said in Leadville that the Glass-Pendery dolo- 

 mite contains from one to two ounces and the Carbonate Mine dolomite from two to 

 six ounces of silver to the ton. 



To complete the discussion of dolomites a few analyses made at various Leadville 

 smelters are given below. The average composition of dolomites, which has been 

 adopted in the discussion on smelting, was derived from them. 



Analysis of a Glass-pendery dolomite once used at the California smelter, made at the time by the superintend- 

 ent, Mr J. E. Hardman. 



Analysis XIII. Dolomite. 



Carbonate of lime -50.03 



Carbon.ate of magnesia 35. 16 



Silica 1. 14 



Protoxide of iron 0.41 



Alumina 2. 62 



Moisture 10. 64 



ICO. CO 



