M3 



obtained as a brown amorphous powder. Deville has also succeeded 

 in crystallizing silicon in " large beautiful needles of a dark iron-grey 

 colour, reddish by reflected light." If this silicon be raised to red 

 heat in the presence of oxygen it formed a white pulverulent substance 

 — silicic oxide. A large cjuantity of it was on the table before them. 

 It was to the problems connected with the occurrences of this sub- 

 stance in Nature in a state of greater or less purity, to the marvellous 

 and beautiful forms which it assumed, and to its relations with other 

 bodies with which we rind it closely connected, that he desired to call 

 their attention that evening. It would be evident that unless we knew 

 some of its more salient chemical properties we should be groping 

 bUndly in the dark -we should be building on an insecure and un- 

 stable foundation. 



The following then were a few which it behoved them well to 

 consider. This oxide of silica, natural as well as artificial, was 

 insoluble in water either hot or cold. All the acids, with one exception 

 (hydrofluoric), were incapable of dissolving it. If water contained in 

 solution any alkaline carbonate— such as carbonate of soda or carbonate 

 of potash — then this silica w-as dissolved to a slight extent. In a hot 

 solution and under pressure the quantity dissolved was greater, and 

 when the liquid was cooled and the pressure removed, the silica was 

 deposited as an opalescent jelly. In aqueous caustic potash or soda it 

 dissolved to a large extent. Water which had carbonic acid in 

 solution, would also dissolve siliceous rocks when under the influence 

 of considerable pressure. Struve had by this means been able to 

 imitate many kinds of mineral water. Alkaline chlorides had also 

 a solvent effect on silica, though not to a great extent. 



And here he must beg them to notice the smaller bottle before 

 him, which contained gelatinous silica. Flint jelly would not, perhaps, 

 be an inappropriate name for it, as it was made from a flint. This 

 was silica, united with the elements of water : hydrated silica. It was 

 slightly more soluble in all solutions than the white powder from 

 which all water had been driven. This distinction of solubility also 

 occurred in Nature, and the hydrated was termed opal-silica. It was 

 not met with in a crystalline or semi-crystalline form, that which was 

 he would term quartz-silica . The distinction between the two was not 

 absolute, but would serve their purpose for the time. Further, the 

 oxide of silica was termed also silicic acid. For this reason. If 



