

DR T. THOMSON'S Analysis of some Minerals. 463 



/ 

 This does not differ very far from the analysis of BOUSSIN- 



GAULT. It is equivalent to 



1 atom sulphate of alumina. 

 6 atoms water. 

 -j^ atom sulphate of soda. 

 ~ atom per-sulphate of iron. 



If we allow the small quantity of sulphate of soda and per- 

 sulphate of iron found in this mineral to be accidental ingre- 

 dients, then the salt is composed of 



1 atom sulphate of alumina, . . . 7.25 

 6 atoms water, . .- 6.75 



14. 



VII. Sulphate of Alumina From Campsie. 



Mr MACINTOSH has an alum-work at Campsie, near Glasgow. 

 The alum is obtained from the shale of the old abandoned coal 

 beds in the neighbourhood. At first, nothing more was neces- 

 sary than to lixiviate the shale, concentrate the liquid, and add 

 sulphate or muriate of potash in order to obtain alum. This 

 process being continued for a considerable number of years, a 

 great quantity of shale thus washed had accumulated in the 

 neighbourhood of the work. Mr MACINTOSH found, that, by 

 burning this washed shale, it might be made to yield a new crop 

 of alum. In one of my visits to this manufactory, Mr MACIN- 

 TOSH pointed out to me thin white bands, which occasionally 

 present themselves in this burnt shale, and he mentioned how 

 very productive these bands were when employed in the manufac- 



