274: PROCEEDINGS OP THE AMERICAN ACADEMY. 



Silico-Molyhdates. 



The existence of definite silico-molybtlates appears to have been 

 first observed by Parmentier,* who obtained potassium, sodium, and 

 ammonium salts by the action of alkaline silicates upon alkaline mo- 

 lybdates in presence of* nitric acid. The free acid has the formula 

 12 M0O3 • Si02 + 26 aq. I have devised another method of prejjar- 

 ing this class of salts, which may perhaps be generalized in its appli- 

 cation. When a solution of fluosilicic acid is poured into one of 14 : G 

 molybdate of ammonium, no precipitate is formed, but the solution be- 

 comes yellow. On evaporation a bright yellow crystalline body sepa-' 

 rates in large quantity. When normal sodic molybdate, Mo04lS[a2, is 

 strongly acidulated with chlorhydric acid, the addition of fluosilicic acid 

 gives at once a bright yellow color. The solution obtained in this 

 manner gives no precipitate in the cold with ammonic chloride, but on 

 boiling and shaking for a few minutes a beautiful bright yellow crystal- 

 line precipitate is thrown down in abundance. Tiiis is slightly soluble 

 in hot water to a yellow liquid. A solution of fluosilicic acid mixed with 

 one of an acid potassic molybdate forms no precipitate, but the mix- 

 ture is yellow, and on evaporation to dryness upon a water bath yields 

 a highly crystalline yellow powder. Much molybdic teroxide is at 

 the same time reduced to blue oxide. The yellow solutions of the 

 silico-molybdates of potassium and sodium give with nitrate of croceo- 

 cobalt a beautiful orange crystalline precipitate, which is insoluble in 

 cold water and readily washed and dried. The bright yellow silico- 

 molybdate of ammonium after careful washing was analyzed : 



0.7963 gram lost on ignition with WOiNaa 0.0750 gram NH3 and 



H.O = 9.42%. 

 0.5279 gram left on ignition 0.0158 gram S : O2 = 2.99%. 

 0.6504 gram gave 0.0339 gram (NH4)20 = 5.22%. 



0.5817 gram gave 0.03045 gram (NH4)20 = 5.23%. 



The analyses correspond to the formula, 



* Comptes Rendus, XCII. 1234, and XCIV. 213. 



