Researches on Artificial Productions of Minerals. 307 
of six languages; Dutch, French, English, Italian, Latin, or 
German. They must be addressed in the ordinary forms of 
competition, to the Secretary of the Society, M. J. G S. 
van Breda, before the 1st of January 1856. 
Researches on the Artificial Production of Minerals, be- 
longing to the family of Silicates and Aluminates, by the 
reaction of Vapour on Rocks. By M. DAUBRKE. 
- Modern geology admits, as demonstrated, a modification 
of rocks in contact with, or in the vicinity of, massive 
erystalline formations. It is this theory which has procured 
for them the designation of metamorphic rocks. 
Since the memorable experiment of James Hall, elevated 
temperature has been admitted as the principal agent of 
metamorphism. But the intervention of heat alone cannot 
explain the important modifications which rocks have under- 
gone*in many countries; complex chemical actions have 
contributed to alter the primitive type. 
- In former researches, which the Academy has condescended 
to receive with favour, I have been principally occupied with: 
_ the mineral formations that contain repositories of tin, and 
the reciprocal reactions of vapours, the one upon the other. 
The new experiment, the results of which I have now the 
honour to submit, along with a few modifications in the 
_ processes, have the same theoretical idea as I commenced 
_ with, and now extend the inquiry to the crystalline or azoic 
rocks. 
_ The chloride of silicium reacting, in a state of vapour and 
_ at the temperature of red heat, on the basis which enter into 
_ the constitution of rocks, becomes decomposed, forming by 
_ the change chloride of calcium and of silicic acid. Some- 
_ times this acid remains free, sometimes it combines in excess _ 
; < _with the base, and forms simple or multiple silicates. 
4 _ This reaction is remarkable in this respect in a chemical 
Fi pec of view, and it is 50 pay 3 in a geological one, that 
: are Poll, but in general very distinetly defined. 
, U3 
