SALTS SULPHITES. 337 



(e.) Magnesia also appears to form a variety of alum, but it has 

 not been applied to use. 



(/.) For a notice of a neutral sulphate of alumina, and for one of a 

 sub-sulphate of alumina and potassa, &ic. see Henry, Vol. I, p. 634, 

 10th ed. Ann. de Chim. et de Phys. VI, 201 and XVI, 355, 

 and Dr. Thomson's First Principles, I, 313. 



SULPHITES OF ALKALIES AND EARTHS. 



General characters. 



1. Taste and smell like that of burning sulphur. 



2. Heat expels sulphurous acid and water, and finally sulphur, 

 which, when inflamed, burns violently, and a sulphate remains.* 



3. Solution slowly absorbs oxygen from the air and becomes sul- 

 phate. 



4. Chlorine and nitric acids convert the sulphites into sulphates ; 

 and nitric acid gives out red fumes. Sulphuric and muriatic acids 

 expel the sulphurous acid with effervescence. 



5. The sulphites are not precipitated by solution of baryta or 

 strontia, or by any of their salts. 



6. They are formed by passing a stream of sulphurous acid gas 

 through the base, dissolved or suspended in water. 



7. The alkaline sulphites are most soluble and crystallizable. 



8. A neutral sulphite, when its acid is oxygenized, always forms a 

 neutral sulphate. 



SULPHITE OF LIME. 



1 . Besides the general method, already mentioned, this salt may 

 be formed from the carbonate. 



2. Insoluble at first, but is dissolved by continuing to pass sulphur- 

 ous acid through it. 



3. Crystallizes in six sided prisms, acuminated by six planes. 



4. Requires 800 parts of water for solution, unless there be an 

 excess of acid. 



5. Proportions, lime 28, sulphurous acid 32, by theory. Brande. 



SULPHITE OF BARYTA. 



1. It may be formed by passing sulphurous acid over carbonate of 

 baryta. 



2. A white powder, little soluble, becomes more so by passing 

 sulphurous acid gas in excess through the powder. 



3. Composition. Baryta 78, acid 40 ; by theory, one proportion 

 of each. 



Except the sulphate of ammonia, which is entirely exhaled 

 43 



