320 Royal Society, 



in a small quantity of hydrochloric acid, without heat, and placing 

 the liquid upon a dialyzer for several days. The liquid must not 

 contain more than 1 per cent, of titanic acid, otherwise it sponta- 

 neously gelatinizes, hut it appears more stable when dilute. Both 

 titanic and the two stannic acids afford the same classes of com- 

 pounds with alcohol &c. as are obtained with silicic 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 remarkable colloid, of which the pectous form alone has 

 hitherto been known. Liquid tungstic acid is prepared by adding 

 dilute hydrochloric acidcarefully to a 5 per cent, solution of tung- 

 state 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 tempe- 

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

 or gelatine, 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. without losing its solubility or passing into the pectous 

 state, but at a temperature near redness it undergoes a molecular 

 change, losing at the same time 2*42 per cent, of water. When water 

 is added to unchanged tungstic acid, it becomes pasty and adhesive 

 like gum ; and it forms a liquid with about one-fourth its weight of 

 water, which is so dense as to float glass. The solution effervesces 

 with carbonate of soda, and tungstic acid is evidently associated 

 with silicic and molybdic acids. The taste of tungstic acid dissolved 

 in water is not metallic or acid, but rather bitter and astringent. 

 Solutions of tungstic acid containing 5, 20, 50, 66*5, and 79'8 per 

 cent, of dry acid, possess the following densities at 19°, 1*0475, 

 1-2168, 1-8001, 2-396, and 3'243. Evaporated in vacuo liquid 

 tungstic acid is colourless, but becomes green in air from the deoxi- 

 dating action of organic matter. Liquid silicic acid is protected 

 from pectizing when mixed with tungstic acid, a circumstance pro- 

 bably connected with the formation of the double compounds of these 

 acids which M. Marignac has lately described. 



Molybdic Acid has hitherto been known (like tungstic acid) only 

 in the insoluble form. Crystallized molybdate of soda dissolved in 

 water is decomposed by the gradual addition of hydrochloric acid 

 in excess without any immediate precipitation. The acid liquid thrown 

 upon a dialyzer may gelatinize after a few hours, but again liquefies 

 spontaneously, when the salts diffuse away. After a diffusion of 

 three days, about 60 per cent, of the molybdic acid remains behind 

 in a pure condition. The solution of pure molybdic acid is yellow, 

 astringent to the taste, acid to test-paper, and possesses much stabi- 

 lity. The acid may be dried at 100°, and then heated to 200° 

 without losing its solubility. Soluble molybdic acid has the same 

 gummy aspect as soluble tungstic acid, and deliquesces slightly when 

 exposed to damp air. Both acids lose their colloidality when digested 

 with soda for a short time, and give a variety of crystallizable salts. 



