[ 68 ] 

 X. Proceedings of Learned Societies. 



nOYAL SOCIETY. 



[Continued from vol. xiv. p. 551.] 



May 7, 1857. — The Lord Wrottesley, President, in the Chaii'. 



TPIE followins; commnnication was read : — 

 "On the i)art which tiie Silicates of the Alkalies may play in 

 the Metan-.orphism of Rocks." By T. Sterry Hnnt, Esq., of the 

 Geological Survey of Canada. 



In my last communication to the Royal Society on the Meta- 

 movphic Siliuian Strata of Canada, I endeavoured to show, from the 

 results of nnnlyses of the altered and unaltered reeks, that it is the 

 reaction hciwc-cn the siliceous m.atters and the carbonates of lime, 

 magnesia, and iron of the sedimentary deposits, which has given rise 

 to the serijcntines, talcs, pyroxenitcs, chlorites, and garnet rocks of 

 t!ie formation. I then cited the observation of Bischof that silica, 

 even in tlie form of pulverized qtiartz, slowly decomposes these car- 

 bonates at a temperature of 2 1 2° F., with evolution of carbonic acid ; 

 the same author mentions that a solution of carbonate of soda has 

 the power of dissolving quartz under similar conditions". Desiring 

 to vorifv these observations, I have since mads the following experi- 

 ments. 



Colourless crystalline quartz was ignited, finely pulverized, and 

 then boiled for an h.our with a solution of its weight of perfectly 

 pure carbonate of soda j the amount of silica thus dissolved was 1-5 

 per cent, of the quartz, but on rcj)eating the treatment of the same 

 quartz with a second portion of the carbonate, only -3') percent, was 

 dissolved. The object of tliis process was to remove any soluble 

 silica, and the quartz thus purified was employed for the following 

 experiments, which were performed in a vessel of platinum. 



I. 1000 parts of quartz and 200 of carbonate of soda were boiled 

 with water for ten hours, and the mixture was several times evapo- 

 rated to dryness, and exposed for a few minutes to a temperature of 

 about 300° F. The amount of silica taken into solution was 12 

 parts. 



II. A hydrocarbonate of magnesia was prepared by mingling 

 boiling solutions of suljjhate of magnesia and carbonate of potash, 

 the latter in excess ; the precijutate was washed by boiling with 

 successive portions of water. 1000 ])arts of quartz were mixed with 

 about as much of this magnesian carbonate and boiled as above for 

 ten hours. An excess of hydrochloric acid was then added, the 

 whole eva[)oratcd to dryness, and the magnesian salt washed out with 

 dilute acid. The residue was then boiled for a few minutes with car- 

 bonate of soda, and gave 33 parts of soluble silica. 



III. A mixture of 1000 parts of quartz, 200 of carbonate of soda 

 with water, and an excess of carbonate of magnesia was boiled for 

 ten hours, and the residue, treated as in the last experiment, gave 148 

 parts of soluble silica. The alkaline liquid contained a little mag- 



* Bischofs Chcra. and Phys. Geology, Enp;. Edition, vol. i. p. 7. 



