METALLURGY. 251 



contain; but that the apparent difference in the analyses of them 

 here mentioned, proceeds rather from the mode of operating than 

 from the substances themselves. But, though future experience 

 should prove that very pure pieces of the calamities we are speaking 

 of do exactly agree to the quantity of air contained in them, it will 

 not follow that the calamines, as prepared for sale by the miners 

 or burners, will be similar to each other in all their properties; 

 since they may be mixed with different quantities and with different 

 sorts of heterogeneous substances, from which it may be impos. 

 sible u holly to free them. 



The reader must not conclude, from what has been said, that 

 all sorts of calamine lose one third of their weight by calcination, 

 or afford fixed air by solution in acids. Bergman analysed some 

 calamine from Hungary, and he found 100 grains of it to consist 

 of eighty. four grains of the earth of zinc, three of the eartli of 

 iron, one of clay, and twelve of siliceous earth: no mention is 

 made of water in thi* analysis.* 



In the great works where calamine is prepared for the brass 

 makers, after it has been properly calcined, by which process, as 

 has been observed, it loses between a third and a fourth part of its 

 weight, it is again carefully picked, the heterogeneous parts hav- 

 ing been rendered more discernable by the action of the fire; it is 

 then ground to a fine powder : afterwards it is washed in a gentle 

 rill of water, in order to free it as much as possible from the 

 earthy particles with which it may be mixed ; for these, being 

 twice as light as the parties of the calamine, are carried off from 

 it by the water : it is then made up for sale. A ton of the crude 

 Derbyshire calamine, as dug from the mine, is reduced, by the 

 various processes it undergoes before it becomes saleable, to about 

 twelve hundred weight : and hence it has lost eight parts in twenty. 

 Of the eight hundred weight thus lost in a ton, 6f may be esteem, 

 ed fixed air: the remaining part, amounting to !-j. consists of 

 some impurities which have been picked out or a s l. i MVJ>, and 

 of some portion of the metallic part of the calamiir-. which is in. 

 flamed and driven off during the calcination: for 1 cannot agree 

 with Walleriusf, in supposing that the on s of zinc lose no part 

 of their substance during the ordinary proofs of calcination; the 

 blue Same which is visible in the finnace where the calamine is 



* Berg. Chem. Ess. vol. II, p. 325. t Meullur. 



