340 Mr. Graham on the Properties of Silicic Acid ^c, [June 16, . 



understood. On the other hand, the gelatinous acid may again he Hquefied 

 and have its energy restored by contact with a very moderate amount of 

 alkah. The latter change is gradual, 1 part of caustic soda, dissolved in 

 10,000 water, liquefying 200 parts of silicic acid (estimated dry) in 60 

 minutes at 100° C. Gelatinous stannic acid also is easily liquefied by a 

 small proportion of alkali, even at the ordinary temperature. The alkali, 

 too, after liquefying the gelatinous colloid, may be separated again from it by 

 diffusion into water upon a dialyzer. The solution of these colloids, in 

 such circumstances, may be looked upon as analogous to the solution of in- 

 soluble organic colloids witnessed in animal digestion, with the difference 

 that the solvent fluid here is not acid but alkaline. Liquid silicic acid may 

 be represented as the " peptone of gelatinous silicic acid ; and the lique- 

 faction of the latter by a trace of alkali may be spoken of as the peptization 

 of the jelly. The pure jellies of alumina, peroxide of iron, and titanic acid, 

 prepared by dialysis, are assimilated more closely to albumen, being peptized 

 by minute quantities of hydrochloric acid. 



Liquid Stannic and Metastannic Acids. — Liquid stannic acid is prepared 

 by dialyzing the bichloride of tin with an addition of alkali, or by dialyzing 

 the stannate of soda with an addition of hydrochloric acid. In both cases 

 a jelly is first formed on the dialyzer ; but, as the salts diffuse away, the jelly 

 is again peptized by the small proportion of free alkali remaining : the 

 alkali itself may be removed by continued diffusion, a drop or two of the 

 tincture of iodine facilitating the separation. The liquid stannic acid is 

 converted on heating it into liquid metastannic acid. Both liquid acids 

 are remarkable for the facility with which they are pectized by a minute 

 addition of hydrochloric acid, as well as by salts. 



Liquid Titanic Acid is prepared by dissolving gelatinous titanic acid in a 

 small quantity of hydrochloric acid, without heat, and placing the Hquid 

 upon a dialyzer for several days. The liquid must not contain more than 

 1 per cent, of titanic acid, otherwise it spontaneously gelatinizes, but it 

 appears more stable when dilute. Both titanic and the two stannic acids 

 afford the same classes of compounds with alcohol &c. as are obtained 

 with sihcic acid. 



, Liquid Tungstic Acid. — The obscurity which has so long hung over 

 ^ tungstic acid is removed by a dialytic examination. It is in fact a re- 

 markable colloid, of which the pectous form alone has hitherto been known. 

 Liquid tungstic acid is prepared by adding dilute hydrochloric acid care- 

 fully to a 5 per cent, solution of tungstate of soda, in sufficient proportion 

 to neutralize the alkali, and then placing the resulting liquid on a dialyser. 

 In about three days the acid is found pure, with the loss of about 20 per 

 cent., the salts having diffused entirely away. It is remarkable that 

 the purified acid is not pectized by acids or salts even at the boiling 

 temperature. Evaporated to dryness, it forms vitreous scales, like gum 

 or gelatin, which sometimes adhere so strongly to the surface of the 

 evaporating dish as to detach portions of it. It may be heated to 200° C. 



