Mr. T. Graham on Liquid Diffusion applied to Analysis. 295 



Table XIV. — Dialysis through Parchment-paper during 

 twenty-four hours, at 12°. 



Two per cent, solutions. 



Chloride of sodium . 



Picric acid 



Ammonia 



Theine 



Saiicine 



Cane-sugar 



Amygdaline 



Extract of quercitron 

 Extract of logwood . 



Catechu 



Extract of cochineal . 

 Gallo-tannic acid .... 

 Extract of litmus .... 

 Purified caramel .... 



Diffusate, 



Proportional 



in grammes. 



diffusate. 



1-657 



1 



1-690 



1 



020 



1-404 





847 



1-166 





703 



•835 





503 



•783 





472 



•517 





311 



•305 





184 



•280 





168 



•265 





159 



•086 





051 



•050 





030 



•033 





019 



•009 





005 



Picric acid and theine were actually diffused from 1 per cent, 

 solutions, and the numbers observed are multiplied by 2. The 

 crystallizable principles, theine, saiicine, and amygdaline, appear 

 greatly more diffusible than gallo-tannic acid, or than gum, as 

 has been already seen. Such inequality of rate is likely to 

 facilitate the separation of vegetable principles by the agency of 

 dialysis. 



4. Preparation of Colloid Substances by Dialysis. 



The purification of many colloid substances may be effected 

 with great advantage by placing them on the dialyser. Accom- 

 panying crystalloids are eliminated, and the colloid is left behind 

 in a state of purity. The purification of soluble colloids can 

 rarely be effected by any other known means^ and dialysis is 

 evidently the appropriate mode of preparing such substances free 

 from crystalloids. 



Soluble Silicic Acid. — A solution of silica is obtained by pouring 

 silicate of soda into diluted hydrochloric acid, the acid being 

 maintained in large excess. But in addition to hydrochloric acid, 

 such a solution contains chloride of sodium, a salt which causes 

 the silica to gelatinize when the solution is heated, and otherwise 

 modifies its properties. Now such soluble silica, placed for 

 twenty-four hours in a dialyser of parchment-paper A to the usual 

 depth of 10 millimetres, was found to lose in that time 5 per 

 cent, of its silicic acid, and 86 per cent, of its hydrochloric acid. 

 After four days on the dialyser, the liquid ceased to be disturbed 

 by nitrate of silver. All the chlorides were gone, with no further 

 loss of silica. In another experiment 112 grammes of silicate of 

 soda, 67*2 grammes of dry hydrochloric acid, and 1000 cub. cents. 



