102 SALINES. [IV. 



passed through, it is weighed moist, then dried at 212° and 

 again weighed. The difference between the two last weights 

 is the water of the solution of sulphate of potassa, which, 

 being of a known strength, gives the quantity of sulphate of 

 potassa it contained. This must of course be subtracted from 

 the weight of the dried residue, and the remainder is the sul- 

 phate of potassa made from the pearlash. If the ash were 

 free from soda, this weight would equal that of the original 

 sulphate evaporated to dryness, but if less, then sulphate of 

 soda has been washed out. From this loss (= L) the car- 

 bonate of soda in the ash may be thus calculated, 



L.53 



71 (NaO,S03) : 53 (NaO,CO,) ::L:xovx = — — 



It must however be observed, that the soda used to adulterate 

 potash usually contains a large percentage of sulphate of soda. 



JVitre is formed in artificial beds, or in some cases where 

 nitrogenous organic matter is present, together with lime and 

 some potash ; but potash is usually added to the beds, or the 

 extract of the soil, containing nitrate of lime, whereby nitrate 

 of potassa is produced. Soda-saltpeter is obtained from At- 

 tacama in Peru. Both nitrates are the source of nitric acid. 



Anhydrous Nitric Acid. — Deville (Comptes Rendus, 1849) 

 has succeeded in obtaining anhydrous nitric acid by the action 

 of absolutely dry chlorine upon nitrate of silver. It crystal- 

 lizes in brilliant, colorless, six-sided prisms ; melts at 85° F. 

 and boils at 113°, and requires to be handled cautiously, owing 

 to its tendency to explode. 



5. Alum. — This most important salt to the dyer, calico- 

 printer, tanner, and others, is sometimes observed in nature 

 in an impure state, but it is generally procured from slates, 

 which have originally contained iron pyrites (sulphuret of 

 iron). The pyrites by oxidation form sulphuric acid, which 

 is more or less transferred to the alumina of the slate ; and to 

 the extracted sulphate of alumina, sulphate of potassa is added 

 and alum generated. As sulphate of iron is obtained inci- 

 dentally in making alum, it leads us to the metallic salts and 

 pigments, or metallosalines. 



