ANALYSIS OF ALUM ORES. QgQ 



residuum left after the distillation of nitric acid, glass gall, 

 &c. The alum meal is washed with cold water, redissolved Crystallization. 

 afterward in a small quantity of boiling water, and lastly 

 drawn off into large wooden vessels, where it is left to cry- 

 stallize slowly. 



I shall now proceed to the proper object of this essay. Analysis 

 namely, the chemical analysis of the alum stone of Tolfa, of To^ifa""""'® 

 and of the earthy aluminous schist of Freienwald. 



I. TJie Alum Ore of Tolfa. 



The alum stone of Tolfa in its natural state contains the Contains all the 

 three essential constituent principles of alum, considered ^^^ential parts 

 as a triple salt ; sulphuric acid, alumine, and potash. The 

 earth in which it is found is probably of volcanic origin, 

 and has been altered and whitened by the vapour of sul- 

 phuric acid. In this it exists in irregular veins, and in no- 

 dules. The harder and heavier it is, the richer in alum it 

 is presumed to be. Some naturalists, as Monnet and Berg- 

 man, have supposed it contained sulphur, which was after- 

 ward converted into sulphuric acid by the process of roast- 

 ing. But Dolomieu and Vauquelin have shown, that this Acid readv 

 acid is ready formed in the ore, which will be farther con- ^^'^'^^^ in Ae 

 firmed by what I shall say. 



The alum stone employed in my analyses was of a pearl Physical charac- 

 gray, that is, gray with a violet tinge ; in amorphous ^^^^ ^^ ^*^'^ '^^'^■ 

 masses; dull, with a few shining points, or having very lit. 

 tie lustre; of an unequal fracture approaching to shelly; 

 a little translucid on the edges; hard, not adhering to the 

 tongue, and heavy. 



A. Two hundred grains were strongly roasted in a small Roasted, 

 retort with its proper apparatus. An aqueous liquor passed 

 over, highly loaded with sulphuric acid, and accompanied 



with a smell of sulphurous acid, but without a particle of 

 sulphur. The loss of weight was twenty nine grains. 



B. Two hundred grains were gently heated, so that the Water expel- 

 loss of weight could proceed only from water expelled. ^^' 



This loss was six grains. 



C. a. Two hundred grains were reduced to fine powder. Fused with 

 mixed with twice as much carbonate of soda, and the whole **^ *' 

 subjected to the action of a fire, at first moderate, but af- 

 terward 



