288 OXIDES. 



This modification of the method is much the most 

 convenient for the production of caustic al- 

 kalies in small quantities. Solutions, useful 

 for a variety of chemical purposes, are thus 

 obtained, and should be preserved for use. 

 They may be converted into solids, by 

 evaporation, and the solid thus obtained fused 

 and run into moulds. The commercial caustic 

 potassa, occurring in slender sticks of white 

 or grey color, is thus produced. 



719. AFFINITY OF POTASSA FOR WATER. 



How can the 



affinity of po- Ordinary potassa, as before stated, 



is a h y drate - But its affinit y for 



water, is by no means yet satis- 

 fied in this form. If exposed in an open 

 vessel, it rapidly attracts moisture from the 

 air. It often dissolves, in the course of a few days, in 

 the water thus obtained. 



720. DECOMPOSITION BY POTASSA. Po- 



What is said . 



of the decom- tassa added to the solution of almost 

 P saitsTyp f o- an y salt > occasions a precipitate. The 

 tassa? potassa takes the acid, and precipitates the 



insoluble base. If the experiment be made with an 

 ammonia salt, the base being volatile, passes off into 

 the air. Experiments may also be made with green, 

 blue, and white vitriols, which are, respectively, sul- 

 phates of iron, copper, and zinc. , 



721. CLEANSING AND CAUSTIC PROPER- 

 EB OF PoxAssA.-If soiled rags be boiled 



perties of po- w i t h a dilute solution of potassa, they will 

 be thoroughly cleansed by the process. 



