ofMnieral Substances. 277 



liquid so as to saturate it, which threw down oxide of iron, weigh- 

 ing when washed and ignited, 28 grains. 



c. After the separation of oxide of iron the residuary liquid 

 was made boiling hot, and carbonate of soda added in excess^ 

 which threw down magnesia weighing after ignition 2 grains. 



B. 



One hundred grains were fused with 500 of nitrate of baryta, 

 and the residuary mass supersaturated with dilute sulphuric 

 acid. The precipitate being separated, the clear liquor was 

 mixed with excess of carbonate of ammonia, filtered, evaporated 

 to dryness, and the residuum ignited in a platinum crucible^ 

 After the escape of the sulphate of ammonia, there remained 19 

 grains of sulphate of potassa, equal to 10 grains of potassa. 



The components therefore of this mineral are as follow : 



Silica 53 



Oxide of iron 28 



Magnesia 2 



Potassa 10 



Water 6 



"99 

 Analysis of the Alum Stone of Tolfa. 

 As this mineral affords alum by lixiviation, sulphuric acid, 

 alumina, and potassa, were to be looked for among its com- 

 ponents. 



A. 

 One hundred grains were strongly heated in a coated glass 

 retort; sulphurous acid, water, and sulphuric acid passed over, 

 but there were no traces of uncombined sulphur. The loss of 

 weight amounted to 29 grains. 



B. 

 Two hundred grains were gently heated so as to drive off 

 water only : the loss amounted to 6 grains. 



C. 



a. 200 grains in fine powder were fused with twice their 

 weight of dry carbonate of soda; the cold mass was jxjwdcrtnl. 



