ANALYSIS OF ALUM ORES. 355 



The difference between these analyses in regard to the re- differ in their 

 spective quantities of the several component parts must *^"^'^'"'^^' 

 have arisen, no doubt, from a difference in the composition 

 of the specimens. 



II. Earthy Aluminous Schist of Freienwald. 

 The mineral that furnishes the alum of FreienAvald owes Alum ore of 



its origin unquestionably to the vegetable kingdom, and an- Freienwald oi" 



^ , , , 3 7 1- vegetable ori- 



pears to be produced by an alteration of brown coal. It gin. 



forms a considerable stratum amid the alluvial formation at 

 Freienwald, which is traversed by galleries for its extrac- 

 tion. At coming out of the mine it is of a brownish black, 

 tender or friable, and very slightly shining. Its fracture 

 in the great is imperfectly slaty; in the small, earthy. 

 When rubbed it takes a lustre inclining to that of wax. It 

 belongs to that species of the argillaceous genus, that is 

 designated in the systems of mineralogy by the term alumi- 

 nous earth (alaunerde). This mineralogical term must not 

 occasion it to be confounded with the simple substance 

 known by chemists under the name of earth of alum (alauri' 

 erde), and it is to prevent this mistake I here employ the 

 denomination of earthy aluminous schist. 



Hitherto this mineral, as well as the true aluminous Mistakenly sup- 

 schist, has been considered as a clay impregnated with ^i- P°^^"'^°'^°"^*''^ 

 ' y r o bitumen and 



tumen and pyrites. It is indeed true, that the earthy schists, pyrites. 

 and still more those that have the consistence of stone, very 

 frequently contain pj^rites : but such ores afford only a very 

 ferruginous alum, and are consequently less fit for the fa- 

 brication of this substance, than for that of vitriol. 



The following experiments, made on alum ores of the The sulphur 

 first quality, will show, that the sulphur they contain is ^°"^^j^'J5'|.'" 

 not combined with the iron in the state of pyrites ; but that with carbon. 

 it appears to form a peculiar combination with carbon. 



A. a. A thousand grains of the ore, in the state in which The ore boiled 

 . , . , . , i'l water. 



at was extracted, were put into a phial with twenty ounces 



of distilled water, and boiled for an hour; when the liquor 



was filtered off, and the residuum lixiviated. What passed 



through the filter was colourless, did not perceptibly change 



blue tegetable tinctures, and had a vitriolic taste. 



b. Half 



