Prof. Graham or the Properties of Silicic Acid §c. 317 



allowed to form more than 1 per cent, of the alcoholic solution, 

 otherwise it may gelatinize during the experiment. If I may be 

 allowed to distinguish the liquid and gelatinous hydrates of silicic 

 acid by the irregularly formed terras of hydrosol and hydrogel of silicic 

 acid, the two corresponding alcoholic bodies now introduced may be 

 named the alcosol and alcogel of silicic acid. 



The alcosol of silicic acid, containing 1 per cent, of the latter, is a 

 colourless liquid, not precipitated by water or salts, nor by contact 

 with insoluble powders, probably from the small proportion of silicic 

 acid present in solution. It may be boiled and evaporated without 

 change, but is gelatinized by a slight concentration. The alcohol is 

 retained less strongly in the alcosol of silicic acid than water is in the 

 hydrosol, but with the same varying force, a small portion of the 

 alcohol being held so strongly as to char when the resulting jelly is 

 Tapidly distilled at a high temperature. Not a trace of silicic ether 

 is found in any compound of this class. The jelly burns readily in 

 the air, leaving the whole silicic acid in the form of a white ash. 



The alcogel, or solid compound, is readily prepared by placing 

 masses of gelatinous silicic acid, containing 8 or 10 per cent, of the 

 drv acid, in absolute alcohol, and changing the latter repeatedly till 

 the water of the hydrogel is fully replaced by alcohol. The alcogel 

 is generally slightly opalescent, and is similar in aspect to the hydrogel, 

 preserving very nearly its original bulk. The following is the com- 

 position of an alcogel carefully prepared from a hydrogel which con- 

 tained 9 '3 5 per cent, of silicic acid : — 



Alcohol.... 88-13 



Water 0'23 



Silicic acid 11*64 



100-00 



Placed in water, the alcogel is gradually decomposed — alcohol diffu- 

 sing out and water entering instead, so that a hydrogel is reproduced. 



Further, the alcogel may be made the starting-point in the forma- 

 tion of a great variety of other substitution jellies of analogous con- 

 stitution, the only condition required appearing to be that the new 

 liquid and alcohol should be intermiscible, that is, interdiffusible 

 bodies. Compounds of ether, benzole, and bisulphide of carbon 

 have thus been produced. Again, from etherogel another series of 

 silicic acid jellies may be derived, containing fluids soluble in ether, 

 such as the fixed oils. 



The preparation of the glycerine compound of silicic acid is faci- 

 litated by the comparative fixity of that liquid. When hydrated 

 silicic acid is first steeped in glycerine, and then boiled in the same 

 liquid, water distils over, without any change in the appearance of 

 the jelly, except that when formerly opalescent it becomes now entirely 

 colourless, and ceases to be visible when covered by the liquid. But 

 a portion of the silicic acid is dissolved, and a ghjeerosol is produced 

 at the same time as the glycerine jelly. A glycerogel prepared from 

 a hydrate containing 9'35 per cent, of silicic acid, was found by a 

 combustion analysis to be composed of 



