338 Mr. Graham on the Properties of Silicic Acid [June 16, 



and is similar in aspect to the hydrogel, preserving very nearly its original 

 bulk. The following is the composition of an alcogel carefully prepared 

 from a hydrogel which contained 9*35 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 diffusing out 

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



Further, the alcogel may be made the starting-point in the formation of 

 a great variety of other substitution jellies of analogous constitution, 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, contain- 

 ing fluids soluble in ether, such as the fixed oils. 



The preparation of the glycerine compound of silicic acid is facilitated 

 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 novi^ entirely colourless, and ceases to be 

 visible when covered by the liquid. But a portion of the silicic acid is 

 dissolved, and a glycerosol 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 



Glycerine 87*44 



Water 378 



Silicic acid 8*95 



100-17 



The glycerogel has somewhat less bulk than the original hydrogel. When 

 a glycerine jelly is distilled by heat, it does not fuse, but the whole of the 

 glycerine comes over, with a slight amount of decomposition towards the 

 end of the process. 



The compound of sulphuric acid, sulphagel, is also interesting from the 

 facility of its formation, and the complete manner in which the water of 

 the original hydrogel is removed. A mass of hydrated silicic acid may be 

 preserved unbroken if it is first placed in sulphuric acid diluted with two 

 or three volumes of water, and then transferred gradually to stronger acids, 

 till at last it is placed in concentrated oil of vitriol. The sulphagel sinks 

 in the latter fluid, and may be distilled with an excess of it for hours without 

 losing its transparency or gelatinous character. It is always somewhat less 

 in bulk than the primary hydrogel, but not more, to the eye, than one-fifth 

 or one-sixth part of the original volume. This sulphagel is transparent and 



