METALLURGY. 249 



ore and cawk, blackjack, and lead ore, bedded together in the 

 same piece of spar. 



The calamine annually raised in Derbyshire, amounts to about 

 1500 tons. Sixty years ago (as I was informed by an intelligent 

 dealer in calamine, whose father was one of the first who dug it 

 in that country), they did not raise forty tons in a year. The 

 Derbyshire calamine does not bear so good a price as that which is 

 gotten about Mendip in Somersetshire ; the former being sold for 

 about forty shillings, and the latter for sixty-five or seventy shil- 

 lings a ton, before dressing : when thoroughly dressed, the Derby, 

 shire calamine may be bought for about six guineas, and the other 

 for eight pounds, a ton. This dressing of the calamine consists, 

 principally, in picking out all the pieces of lead ore, limestone, 

 iron stone, cawk, and other heterogeneous substances which are 

 mixed with it, when it is first dug from the mine ; this picked cala. 

 mine is then calcined in proper furnaces, and by calcination it 

 loses between a third and a fourth of its weight. 



The substance which is lost during calcination of the calamine 

 is not either sulphur or arsenic, or any thing which can be col. 

 lected by the sides of an horizontal chimney, as is the case in some 

 sorts of copper and lead ores , hence it would be quite unservice- 

 able to roast calamine in a furnace with such a chimney. The 

 truth of this remark will appear from the following experiment. 



1 took 120 grains of the best Derbyshire calamine, and dissolved 

 them in a diluted vitriolic acid : the solution was made in a Flo. 

 rence Flask, and the weight of the acid and flask was taken before 

 the solution commenced. About twenty hours after the solution 

 had been finished, I weighed the flask and its contents, and found 

 that there had been a loss of forty grains, or one third the weight 

 of the calamine ; about a grain of earth remained at the bottom 

 undissolved. If the same quantity of the purest limestone had 

 been dissolved in the same way, there would have been a loss of 

 weight equal to fifty-four grains : the substance which is separated 

 from calamine by calcination, or by solution in an acid, is of the 

 same nature with that which is separable from limestone by the 

 same processes fixed air. This air having the property of chang- 

 ing the blue colour of vegetables to red, as well as many other 

 properties of an acid, and being contained in great abundance in 

 the atmosphere, has been called by some, aerial acid; and by 



