240 ALKALIES. 



This substance, mixed with lime, and fused and cast in cylindrical 

 moulds, forms the caustic called lapis infernalis, or lapis causticus 

 of the shops. It is said that' oxygen gas is disengaged, during its so- 

 lution in water, and that it varies apparently with the impurity of the 

 specimen. 



(c.) It is now caustic, but contains all the soluble impurities, chief- 

 ly salts, carbonate, muriate, and sulphate of potassa, silex, and oxide 

 of iron and manganese, &c. ; to purify it, dissolve it in good alcohol ; 

 the solution will be wine red ; the watery solution of the salts be- 

 low is immiscible with the alcoholic solution of the alkali, and the solid 

 impurities are at the bottom. Evaporate the alcohol,* and finish the 

 process in a silver basin or crucible, with moderate ignition ; then 

 break up the mass, and secure it from the air. 



It still contains a little carbonic acid, arising from the reaction of 

 the alkali on the alcohol, or absorbed from the air. The addition of 

 barytic water, previous to the last evaporation, will entirely remove 

 the carbonic acid. 



(d.) Hydrate of Potassa. This is the substance above described. 



If the whole of the alcohol be not expelled, the alkali will, on cool- 

 ing, crystallize in single or double plates, needles, or tetrahedral py- 

 ramids. This hydrate contains one proportion of water, 9, and one 

 of potassa, which, as we shall see under potassium, is represented by 

 48, and its equivalent is therefore 57. Heat alone will not separate 

 the water from it ; if it is urged, the alkali will rise along with the 

 water, which can be separated only when it enters into new combina- 

 tions. 



4. PROPERTIES. 



(a.) Solid at common temperatures ; melts at 300, and is vola- 

 talized at low ignition, with a visible cloud of caustic fumes, highly 

 acrid ; color, white or gray ; taste, when strong, burning and in- 

 tolerable ; corrodes and destroys animal and vegetable substances, 

 subverting completely the organic texture, and in a word, it posses- 

 ses, in perfection, and in full energy, all the characters of alkalies, 

 mentioned in the introduction to their properties. 



(6.) It affects vegetable colors as ammonia does ; in addition to 

 the colors enumerated under ammonia, it may be mentioned that a 

 strong infusion of the dried flowers of the red rose, answers very 

 well. Parkes. 



(c.) Deliquesces rapidly in the air, and by absorbing carbonic 

 acid, becomes partially mild again. It acquires moisture so rapidly, 



* Or distil off and save the first half of it, in a receiver, as it will be alcohol of a 

 good quality ; the remainder will contain more water, and is scarcely worth sa- 

 ving ; there is danger, besides, if we evaporate too low in a glass vessel, that it will 

 be attacked by the alkali. 



