Intelligence and Miscellaneous A?'ticles. 385 



relation to those phsenomena which are produced solely by electro- 

 chemical forces. The new results which I now make known, testify 

 to the fecundity of the methods of investigation by means of which 

 we may determine the play of affinities in the contact of solids with 

 liquids. 



Silica and Quartz (Si O*^). — Silica generally occurs in the form of 

 quartz, insoluble in alkalies, and sometimes in a hydrated state so- 

 luble in alkalies, as in opal, and the deposits formed by mineral 

 waters. We are indebted to M. Ebelmen for some interesting 

 researches on the artificial production of hydrated silica in a hard 

 transparent state, like rock crystal, by exposing silicic aether to 

 the action of moist atmospheric air ; this silica has the formula 

 2Si03 + 3HO, and its density is 1*770. These conditions are obvi- 

 ously not those under which silica has been formed naturally. 



On the other hand, M. de Senarmont has shown that by heating 

 under pressure a solution of silica, in water saturated with carbonic 

 acid, or in weak hydrochloric acid, to 392° or 572° Fahr., anhydrous 

 silica is obtained in the form of quartz, and insoluble in all reagents 

 except hydrofluoric acid. It is probable that quartz has actually 

 been formed in this way in nature, for the conditions are such as 

 may co-exist at a certain depth below the surface of the earth. 



Further, M. Fremy has recently succeeded in obtaining solid 

 hydrated silica by decomposing sulphuret of silicium by water, and 

 under conditions which may coexist naturally. Mr. Cross has, by 

 means of a voltaic battery consisting of a great number of couples 

 weakly charged, slowly decomposed a solution of silica in potash or 

 hydrofluoric acid, in such a manner as to obtain at one of the poles, 

 according to the chemical relation of the silica in the compound, 

 prismatic crystals of quartz with pyramids at their summits. This 

 mode of production may not be one which takes place naturally, but 

 the fact is deserving of notice. 



I have endeavoured to ascertain whether it may not be possible, 

 by means of the method of double decomposition, which has already 

 enabled me to obtain malachite (hydrated bibasic carbonate of 

 copper) and a number of other compounds, to produce quartz and 

 hydrated silica. For this purpose I introduced into a flask, fur- 

 nished with a loosely fitting cork, a very weak solution of silicate 

 of potash (about half a litre), with a number of plates of sulphate 

 of lime. Carbonic acid gradually penetrated in the flask, giving rise 

 to the formation of carbonate of potash, which immediately acted upon 

 the sulphate of lime, producing sulphate of potash and carbonate of 

 lime, which crystallized, while silica was precipitated sufficiently hard 

 to scratch glass, and forming granules or plates of 5 or 6 centimetres 

 superficies. These plates showed a tendency to assume a coralloid 

 structure ; the silica of which they consisted contained 12 per cent, of 

 water. Silica was likewise deposited at the bottom of the flask in 

 very delicate particles, having the same hardness as the above, which 

 when treated with a hot solution of potash, left at the bottom of the 

 capsule transparent lamellae, which gave, between two Nichol's 

 prisms, the colours presented by crystals causing double refraction, 



