NEITHER POTASH NOR AMMONIA. 44/7 



1 atom sulphate of'lime 8-5 



1 atom sulphate of soda 9 



17-5 



As is evident from the analysis of Brogniart. 



5. Soda-sulphate of alumina, or soda-alum. Soda alum. 

 This species of alum has been hitherto over- 

 looked by chemists, in consequence of its great 

 solubility, and the consequent difficulty of ob- 

 taining it in regular crystals. I have been in. 

 formed by my friend, Charles Macintosh, Esq. of 

 Glasgow, that he made it more than twenty 

 years ago. For the specimen which I examined, 

 I am indebted to Mr. John Wilson of Hurlet, 

 who first drew my attention to it, and furnished 

 me with very pure specimens. The salt was 

 noticed in 1810, by Mr. Winter, in his account 

 of the Whitby alum processes.* In appearance, 

 soda-alum cannot be distinguished from common 

 alum ; the crystals are regular octahedrons, or 

 forms obviously derived from the common octa- 

 hedron : the taste is the same as that of com- 

 mon alum. It undergoes no alteration from ex- 

 posure to the air, if pure, but it is frequently 

 impure, and in that case effloresces on the sur- 

 face. The great solubility of this alum is its 

 great characteristic property. It is more than 

 thirty times more soluble in cold water than 

 ammoniacal alum, and more than twenty times 



* Nicholson's Jour, XXV. 254, 255. 



