METALLURGY. 



calcined, and the injury which the calamine sustains from \n 

 calcined with too strong a fire, arc proofs lo the contrary. It would 

 be possible to use calamine for the purpose of making brass with- 

 out calcining it; for the fixed air would be dissipated by the heat 

 applied in making the brass. But, as in using a ton of uncalcined 

 calamino, there would be between six and seven hundred weight 

 put into the brass pots which would he of no manner of use in the 

 operation, it is a wiser method to get rid of so large a quantity of 

 unserviceable matter ; especially as the carriage of six or seven 

 hundred weight to the distance to which the prepared calamine is 

 Bent for the making of brass, would cost more than the calcination 

 of a ton of it amounts to. 



There are many sorts of blende or black jack, which differ 

 from each other not only in their external appearance, but in their 

 internal constitution. In general they contain zinc and sulphur, 

 united together by the intervention of iron, or of calcareous earth; 

 and they must be previously freed from their sulphur by calcina. 

 tion, before they can be applied to the making of brass. Some 

 sorts of blackjack lose one. fourth, others about one. sixth of their 

 weight by calcination : what is thus dispersed consists principally 

 of sulphur, with a little water; what remains consists of a large 

 portion of zinc earth, mixed with one or more of the following 

 substances, viz. iron, lead, copper, clay, and flint. Blackjack 

 is found in North Wales, in Cornwall, and in Derbyshire; and 

 probably it may be met with in many other parts of Great Britain. 

 It has for many years been used, as well as calamine, for the 

 making of brass at Bristol ; and 1 believe it was first used there 

 under a patent : but so little was this application of it known in 

 other parts of the kingdom, that in the year 1777, they begged 

 me in Derbyshire (where they had a little belore that time began 

 to save it) not to divulge the purpose to which it might be applied. 



It has not been long well understood, that either calamine or black 

 jack contained any metallic substance. Matthiolus, Agricola, Ca. 

 neparius, and other expert and more ancient metallurgists, esteem, 

 ed calamine to be a mineral in which there was no metallic sub- 

 stance*. Their mistake on this subject was very excusable; for 

 the metallic substance contained in the calamine being of a volatile 

 and combustible nature, it consumed or dissipated by the ordinary 



* Canep. de Atram. p. 12 SI. 



