TRANSACTIONS OP THE SECTIONS. 51 



4700 tons from Swaledale, and Wharfdale, Pateley Bridge, &c. yield 

 on an average only 2 oz. per ton. The lead of Derbyshire and Shrop- 

 shire, 4800 tons, from 1 oz. to li oz. only. The lead of Cornwall and 

 Devon, 2000 tons, is rich in silver, so as to yield on an average 20 to 

 30 oz. per ton ; half of that from Flintshire and Denbighshire, contains 

 from 4i to 6A oz., and the other half 9 or 10 oz. 



The ordinary process of cupellation or refining*, consists in the 

 oxidation of the lead, kept at a red heat, and traversed by a current of 

 air ; the silver remains nearly pure ; the oxide of lead is either re- 

 duced, or sold as litharge. The cost of this process and the waste of 

 lead are so considerable, that with lead at the price of 20/. the ton 

 from 6 to 8 oz. of silver are required to barely cover the whole charge 

 against the operation. About 18,000 tons of the whole quantity raised 

 in England and Wales are supposed to undergo the refining process ; 

 and the waste of lead upon the ^vhole quantity would amount to 1 000 

 tons. Where the lead before refining was impure, with admixture of 

 other metals, its quality is improved by the process, sometimes to the 

 value of 10s. a ton ; but this is only the case in small quantities. 



The desirableness of some more economical mode of extracting silver 

 from lead has been long obvious to those conversant with that branch 

 of our national industry ; and Mr. Pattinson had for some years been 

 engaged in occasional experiments on the subject. Among these, he 

 describes the attempts which he vainly made to separate the lead from 

 the silver by distillation and long-continued fusion. 



Various other experiments were tried by the author, both in the dry 

 way and by the application of liquid menstrua, all of which were un- 

 successful ; but during their prosecution in the month of January 1 829, 

 he required lead in a state of powder, and to obtain it, adopted the 

 mode of stirring a portion of melted lead in a crucible, until it cooled 

 below its point of fusion, by which the metal is obtained in a state of 

 minute subdivision. In doing this he was struck with the circumstance, 

 that as the lead cooled down to nearly its fusing point, little particles 

 of solid lead made their appearance, like small crystals, among the li- 

 quid lead, gradually increasing in quantity as the temperature fell. 

 After observing this phenomenon once or twice, he began to conceive 

 that possibly some difference might be found in the proportions of sil- 

 ver held by the part that crystallized, and the part that remained liquid. 

 Accordingly, he divided a small quantity of lead into two portions, 

 by melting it in a crucible, and allowing it to cool very slowly with con- 

 stant stirring until a considerable quantity crystallized, as already men- 

 tioned; from which the remainder, while still fluid, was poured off: an 

 equal weight of each was then submitted to cupellation, when the button 

 of silver from the liquid lead was found to be very riiuch larger than 

 that from the crystallized lead ; proving that argentiferous fluid lead 

 suffers a portion of silver to escape from it, under certain circumstances, 

 in the act of becoming solid. 



* See Mr. Sadler's Essay in Nicholson's Journal, vol. xv,, and Mr. Pattinson's paper 

 in Newcastle Transactions, vol. xi. pt. I, 



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