Intelligence and Miscellaneous Articles. 325 



rated, adding to it several fragments of pure hydrate of potash so as 

 to render it very caustic. A few drops of the solution are tried from 

 time to time to see whether on cooling they become crystalline ; 

 and when this takes place the evaporation is to be discontinued, the 

 meta-antimoniate of potash then crystallizing abundantly ; the alka- 

 line solution is to be poured off, and the salt is to be dried on por- 

 celain plates. 



This salt always contains an excess of alkali ; it ought to be washed 

 two or three times before it is used as a reagent. As the meta- 

 antimoniate of .potash decomposes in solution in water, it is proper 

 to keep it in the dry state, and to dissolve it at the moment in which 

 the trial is to be made. 



To make an examination, which scarcely requires ten minutes, 

 about fifteen grains of the potash to be tried should be dissolved in 

 a small quantity of water and supersaturated with hydrochloric acid, 

 and the solution is to be evaporated to dryness in a porcelain or 

 platina capsule. The chloride of potassium, being then perfectly 

 neutral, is redissolved in water and treated with the solution of meta- 

 antimoniate of potash. If the potash contains 2 or 3 per cent, of 

 soda, a precipitate is almost instantly formed ; but if the quantity be 

 smaller, time and agitation will be necessary to effect precipitation. 



M. Fremy states the sensibility of this reagent to be so great, that 

 he found by synthetic experiments he could detect a half per cent, 

 of carbonate of soda in commercial potash. — Ann. de Ch. et de Phys., 

 Aout 1848. 



SOLUBILITY OF THE HYDRATES OF COPPER AND CHROMIUM, 

 ETC. IN POTASH AND SODA. 



M. Fremy observes, that when hydrate of copper, precipitated from 

 the sulphate by great excess of potash, is washed and dried in vacuo, 

 it is represented, according to his analysis, by the formula CuO, 

 2HO. In this state it is perfectly soluble in concentrated solutions 

 of potash and soda,' as stated by Proust, forming solutions of a fine 

 blue tint, the hydrate of copper thus consequently acting as an acid. 

 If these solutions be subjected to ebullition, the hydrated oxide of 

 copper is decomposed ; the oxide, becoming anhydrous, completely 

 loses its solubility in the alkalies, and precipitates. 



The influence which water appears to exercise on the acidity of 

 certain hydrates, is shown more remarkably with the sesquioxide of 

 chromium. If a salt of this oxide be precipitated by potash, and the 

 precipitate be washed with cold water and then dried in a current 

 of dry air at common temperatures, a hydrate is obtained which is 

 totally soluble in the alkalies, forming soluble green salts which have 

 been properly called ckromites. This hydrate is composed of — 



Hydrated oxide of chromium 0*519 

 Water 0-268 



