the Chemistry of Geology. 251 



doubtless was, very different. It was not necessary, however, 

 to have recourse to this mode of reasoning. Substances, he 

 said, which are inappreciably soluble in one state, may be freely 

 dissolved in another. Silex in the finest powder may be boiled 

 in water without perceptible solution ; but if presented to that 

 solvent while in the nascent state, it was freely dissolved. Sub- 

 stances in the act of being formed from their elements, or of se- 

 parating from previously existing combinations, do not possess 

 that force of aggregation which properly belongs to them, and 

 in such states of transition they have a peculiar aptitude to com- 

 bine with other bodies. This property is observed more or less 

 in all bodies, but silica offers one of the most striking illustra- 

 tions of it. Siliceous earth, in its nascent state, is freely soluble 

 in water, and in various acid and saline solutions, which do not 

 perceptibly dissolve ordinary flint, however finely it may be 

 pulverized ; and the alkalies and alkaline carbonates, which dis- 

 solve silex even in its solid condition, take it up while nascent 

 in far greater quantity. Now, in the decomposition of felspathic 

 rocks, which had been referred to in the first part of the lecture 

 expressly with a view to that subject, the silex was exposed to 

 the united action of water and alkali at the moment of passing 

 from the state of combination which constitutes felspar, and 

 would be expected to be freely dissolved. That it was so, 

 might be proved by a comparative view of the constitution of 

 porcelain clay and felspar. He would represent their compo- 

 sition, he said, by a formula expressive of the number of equi- 

 valents of each element ; though, in doing so, he did not mean 

 to assert that porcelain clay was strictly an atomic compound. 

 Thus: 



Felspar. Porcelain Clay. 



(p o + 3 s i),+ (Ai.t,?!') ; (A/ + 3 i S i). 



The lecturer stated, that the porcelain clay referred to was a 

 sample from Villarica, which he had analyzed during the course 

 of the winter. -Besides aluminous and siliceous earth, it con- 

 tained 21.3 percent, of water. Mr Rogers of Philadelphia had 

 obligingly analyzed for him some porcelain clay from the vici- 

 nity of Mont Dor in Auvergne, which had a similar constitu- 



