
202 PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 
acid would be apt to come out too low for the solubie silicates, and too high 
_ for the insoluble ones.’ 
In consequence of this conflict of opinion, and being as much puzzled as 
Mr Young, I made the following series of experiments :— 
1. Is soluble Silica converted by a high and long-continued heat into insoluble 
Silica? 
1st... A quantity of impalpable silica was prepared by the fluosilicic acid 
process. This silica, after thorough air drying, was found to lose 9°854 per 
cent. of water when heated to 212° Fahr. It was.found to be then almost 
totally soluble in hot sodium carbonate solution. It was now cautiously heated 
and kept at a barely visible red heat for five minutes. After this treatment 
9-9 per cent. were found to be insoluble. Another portion of the same make 
was heated to the highest heat of a fine Bunsen burner for seventy-five 
minutes, of this 75°19 per cent. were insoluble. | 
The specific gravity of this powder was not taken, but if it be tridymite the 
above silica is the best variety to employ in the manufacture of that modification. 
2d. A piece of perfectly limpid and colourless rock crystal was powdered, 
fused with flux, and obtained as recognised silica—entirely in the granular 
form. After drying in the water bath it. was soluble all but -397 per cent. 
By the same treatment as first applied to the impalpable silica, it yielded 
4:492 per cent. of insoluble ; while by the same treatment as secondly applied 
to the impalpable, it yielded 6°963 per cent. of insoluble. 
A continuous high heat, therefore, converts soluble into insoluble silica ;—and 
the finer the state of division of the silica, the greater the pr opor tional amount so © 
converted. 
2. What amount of influence upon the solubility of the “Silica” is affected by 
over-heating during the granulation of the saline mass? And what is che 
cause of this influence ? 
The pseudo hypersthene (augite) of Oaniiek was found when granulated in’ 
the water bath. at a temperature of a 186° to give a “silica” of which 23:4 per 
cent. was insoluble. The same mineral was granulated in the hot air bath at 
a temperature of 320°, when’53°98 per cent. were found to be insoluble. 
Anthophyllite from Hillswick, Shetland, was found when granulated over 
the water bath to give a silica of which 2°87 was insoluble ; the same mineral, 
treated and granulated at 270° in the hot air bath, gave a silica, 7°25 per cent. 
of which was insoluble. 
Andesine, from Portsoy, at the i heat granulation, gave a silica with 8° 9 
per cent. insoluble ; when granulated at 380°, 71°25 per cent. were insoluble. 
The low heat insoluble silica from the augite was found to contain only 
