ANALYSIS OF ALUM OKES. 3g9 



tt The liquor was evaporated to dryness, and the resi- Sulphate and 

 duum heated till no more white fumes were expelled. What ^JJ!'^'*^ °^ ^°*" 

 remained weighed 4-5 grains. It was a neutral salt, formed 

 of a mixture of sulphate and muriate of potash. As this 

 last salt must necessarily have been completely formed in 

 the ore, we may admit too, that the potash of the former 

 was not free in it, but formed a real component part of it 

 in the neutral state. Till experiments on a larger scale shall 

 have enabled me to determine more accurately the propor- 

 tions of these two salts, I shall reckon that of sulphate to 

 that of muriate as three to one. 



F. The results of the experiments above given m ill serve Corrections of 

 to rectify some of our chemical ideas respecting the earthy ""f^^'^^^ "»• 

 aluminous schist of Freienwald, and those of a similar 



nature. 



1. In their composition there is carbon only, but not The ore con- 

 bitumen; for they afford no bituminous oil by distillation, i^j^i^ j^^ ^-^^j.' 

 and when roasted in open vessels they burn like charcoal nien 

 without flame or suioke. 



2. The sulphur of the ore, which becomes oxigenized The sulphur 

 during its exposure to the air, and thus forms the sulphuric bon la a pec?-'^' 

 acid necessary for the production of alum, is not combined liar way : and 

 in it in the state of pyrites, exclusively of any pyrites mixed pyntes.™'"^ 

 with the ore accidentally, but is intimately united with the 



carbon, and this in a manner with which we are not yet 

 well acquainted. With the best lenses Ave cannot discover 

 the smallest atom of pyrites in the ore, either in its natural 

 state, or after it has been triturated and washed through the 

 sieve with care*. In this state of combination with carbon 

 the sulphur is protected against the solvent power of alka- 

 lis, and gives no sulphuretted hidrogen gas with muriatic 

 acid. 



G. As to the determination of the respective proportions Difficult to Ue- 

 of the constituent principles mentioned, there is some diffi- p'^'^'J^'JJj^^Jj^^ ^^^ 



* I have observed in several coal-mines, particularly those of Firedamp not 

 Anzin, a fact, that has probably some connexion with this men- ^'■o'" pyues. 

 tioned by Mr. Klaproth. The coal that produces fire damps does 

 not contain any pyrites, at least perceptible to the eye ; and in the 

 same places the coal that contains a great deal of pyrites is wrought 

 without the least danger. 



Vol. XX.— Supplement. 2 B culty 



