384 Dialysis. 



so as to affect the nerves of taste. The solution of silica 

 remains for some time perfectly limpid, but eventually sets 

 into a firm jelly. This alteration may be brought about immedi- 

 ately by the presence of several substances, particularly by any 

 earthy carbonate such as chalk. This solution of pure silica 

 possesses remarkable properties ; it is absorbed by gelatinous 

 tissues such as the skin of animals, in the same manner as 

 tannin ; and like it converts them into a kind of leather, which 

 possesses the remarkable property of not putrefying when kept 

 moist. In the same manner a solution of pure peroxide of iron 

 may be obtained, by first dissolving excess of the hydrated 

 oxide in hydrochloric acid, and then dialysing, when a colloid 

 solution of oxide of iron remains, that is capable of being 

 gelatinized like the silica. 



Prussian blue, which is insoluble in pure water, is capable, 

 when recently precipitated, of being dissolved by the aid of 

 gentle heat in a solution of one-sixth of its weight of oxalic acid, 

 when it forms the well-known permanent blue ink. If such 

 a solution be dialysed, the Prussian blue, is in the course of a 

 few days, obtained in a solution in pure water, and may be 

 rendered gelatinous by the addition of sulphate of zinc and 

 several other metallic salts, as the solution of silica is gelati- 

 nized by the addition of carbonate of lime. 



Such are a few of the many examples of these remarkable 

 phenomena. They are as yet of too recent discovery to have 

 been applied to many practical purposes, but a vast number of 

 applications at once suggest themselves. In cases of the sus- 

 pected poisoning of articles of food, the poison, if a crystalloid 

 substance like arsenic, can be readily dialysed and obtained in 

 a pure form, however heterogenous may be the mixture in 

 which it is contained. 



Dyeing will be greatly facilitated by steeping a fabric in a 

 pure solution of some colloid dye, which will unite with the 

 animal or vegetable fibre as it gelatinizes. 



The purification of many drugs, and the separation of dif- 

 ferent substances in the chemical arts will be rendered much 

 easier than heretofore. In fact there appears scarcely a limit 

 to the application of this principle. Already, as may be seen 

 by the report of Mr. Church's paper, read before the Chemical 

 Society, and reported in our second number, page 150, dialysis 

 has thrown light upon obscure points in geology, such as the 

 formation of flints and other silicious fossils, and it promises 

 equally to benefit physiological research. In fact, humble and 

 inconspicuous as its phenomena may appear at first sight, it is 

 probable that in its influence on science and art, it will greatly 

 surpass any discovery of late years. 



