CAROBNATES. 



377 



borne acid 31.50, alkali 68.83. The ignited carbonate contains no 

 water, but there is in common salt of tartar from twelve to sixteen per 

 cent. 



3. PROPERTIES. 



(a.) As it occurs in the shops, it is never crystallized ; the pearl- 

 ashes are always a white porous mass ; the potashes are firm, and of 

 a grey, reddish, or dark color, and both are impure, being mixed, 

 usually with silica and different salts, as the muriate and sulphate of 

 potassa. 



(b.) Very deliquescent, and in the air, becomes in a few hours, 

 semi-fluid. 



(c.) Gives carbonic acid gas by other acids and by heat; alka- 

 line to the taste, turns blue vegetables green, and is even somewhat 

 acrimonious, but does not destroy the texture of woolen cloth. 



(d.) Does not absorb carbonic acid from the air, nor yield any- 

 thing to alcohol. 



(e.) Soluble in less than 1 part of cold water, and cannot be freed 

 from it without considerable heat. 



(/.) Taste much milder than that of the caustic alkalies. 



4. METHODS OF DETERMINING THE QUANTITY OF REAL ALKALI. 

 (a.) Potassa precipitates alumina from alum, which its impurities 



will not do ; hence, the quantity of earth thus precipitated, indicates 

 the proportion of alkali. 



(b.) By nitric acid, which does not dissolve the impurities of the 

 salt.* 



(c.) The proportion of carbonic acid indicates the proportion of 

 alkali. In a balance, place in one scale the alkali and diluted sul- 

 phuric acid, in different vessels ; counterpoise them ; men add the 

 acid to the alkali ; the loss of weight is carbonic acid, and implies 

 about twice as much alkali. 



(d.) The solubility in water is a tolerable criterion. Most of the 

 impurities, especially sulphate of potassa and silica, being insoluble, 



* TABLE BY VAUQUELIN. 



48 



