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



represented by NaO -f 36Si0 2 (Gmelin). This silicate is probably 

 a co-silicate of soda in the pectous condition. Soluble silicic 

 acid produces a gelatinous precipitate in lime-water, containing 

 6 per cent, and upwards of the basic earth. This and the other 

 insoluble earthy co-silicates appear not to be easily obtained in 

 a definite state. They gave out a more basic silicate to water on 

 washing. The composition of these salts and that also of the 

 co-silicate of gelatine were found to vary according as the mode 

 of preparation was modified. When a solution of gelatine was 

 poured into silicic acid in excess, the co-silicate of gelatine formed 

 gave, upon analysis, 100 silicic acid with 56 gelatine, or little 

 more than half the gelatine stated above as found in that com- 

 pound prepared with the mode of mixing the solutions reversed. 

 The gallo-tannate of gelatine is known to offer the same variability 

 in composition. 



The gelatine used in the preceding experiments was isinglass 

 (colle de poisson) purified by solution in hydrochloric acid and 

 subsequent dialysis. As the acid escapes by diffusion, a jelly is 

 formed in the dialyser. This jelly is free from the earthy matter, 

 amounting to about 0*4 per cent., in isinglass, and is not liable 

 to putrefaction. 



Cosilicic acid also precipitates both albuminic acid and pure 

 caseine. 



Soluble Alumina. — We are indebted to Mr. Walter Crum for 

 the interesting discovery that alumina may be held in solution 

 by water alone in the absence of any acid. But two soluble 

 modifications of alumina appear to exist, alumina and metalu- 

 mina. The latter is Mr. Crum's substance. 



A solution of the neutral chloride of aluminium (A1 2 C1 3 ), 

 placed on the dialyser, appears to diffuse away without decom- 

 position. But when an excess of hydrated alumina is previously 

 dissolved in the chloride, the latter salt is found to escape by dif- 

 fusion in a gradual manner, and the hydrated alumina, retaining 

 little or no acid, to remain behind in a soluble state. A solution 

 of alumina in chloride of aluminium, consisting at first of 52 

 parts of alumina to 48 of hydrochloric acid, after a dialysis of 

 six days, contained 66*5 per cent, of alumina ; after eleven days 

 76*5 per cent. ; after seventeen days 92*4 per cent. ; and after 

 twenty-five days the alumina appeared to be as nearly as possible 

 free from acid, as traces only of hydrochloric acid were indicated 

 by an acid solution of nitrate of silver. But in such experi- 

 ments the alumina often pectizes in the dialyser before the 

 hydrochloric acid has entirely escaped. 



Acetate of alumina with an excess of alumina gave similar 

 results. The alumina remained fluid in the dialyser for twenty- 

 one days, and when it pectized was found to retain 3*4 per cent. 



