1890.] Occurrence of Silver in Volcanic Dust 279 



The specific gravity was found = 2'597 at 25° 0., as compared with, 

 water at the same temperature. 



The ash was fusible, though with difficulty, before the mouth blow- 

 pipe, or in a small platinum spoon or crucible over the blast lamp, 

 forming a greenish vesicular slag, red on the surface. 



On being boiled with water it gave up 0*13 per cent, of soluble 

 matter. This portion, soluble in water, consisted mainly of sodium 

 sulphate and chloride, with a little of the corresponding salts of 

 potassium and traces of yellowish-brown organic matter. 



Treatment with dilute hydrochloric or even acetic acid produced 

 quite noticeable effervescence. On digestion with gentle warming in 

 rather dilute acetic acid, 336 per cent, dissolved, of which 2'83 per 

 cent, was calcium carbonate, - 31 per cent, magnesium carbonate, and 

 the rest minute amounts of iron, aluminum, and the alkaline salts 

 soluble in water. 



On being boiled with strong hydrochloric acid the ash (not having 

 been previously treated with water or acetic acid) dissolved to the 

 extent of 9 61 per cent., the solution having a dark yellow-brown 

 colour, due to the presence of iron. 



The material taken as a whole, i.e., without any previous mechanical 

 separation of its constituent minerals, and without previous digestion 

 with water or acid, but dried at 100° C, gave on analysis the following 



results* : — 



Si0 2 61-49 



Ti0 3 0-18 



Al 2 6 3 16-05 



Ee 2 3 2-84 



EeO 2-48 



MnO trace 



MgO 1-04") besides the MgC0 3 and 



CaO 3-39 / OaCOg stated below. 



rTa 2 6-85 



K 2 2-14 



Li 3 trace 



Ag 



CI 



so 4 



Organic matter .... 



CaC0 3 2-83 



MgC0 3 0-31 



H 2 0-27 



99-87 



* For comparison with, these results may be quoted the following : — 



A. Abich's analysis of the rock, andesite, from the summit of Chimborazo. (Gr. 



