Great Exhibition of 1851. 137 



which has been of such service to lead-mining generally, rendering 

 many lead-mines workable with profit which must otherwise have 

 been abandoned. The chief ore whence lead is extracted is that 

 known as galena, or the sulphuret of lead, furnishing from seventy- 

 five to eighty-three parts of the metal according to purity. It 

 usually, though not always, contains silver in variable propor- 

 tions. Upon the quantity of silver often depends the profitable 

 raising of the ore. Previous to the invention of Mr Pattinson (of 

 Newcastle-upon-Tyne), about twenty ounces of silver in the ton 

 of lead were required to render the extraction of that metal worth 

 the cost ; since then as little as three and four ounces in the ton of 

 lead will repay extraction. Now, as so many ores contain small 

 quantities only of silver, the importance of the process is evident. 

 In a scientific point of view it is one of much interest, as it consists 

 in so conducting the work that portions of the lead can crystallise, 

 by which the silver becomes excluded, in the manner in which, 

 in many crystallising processes, foreign substances are excluded 

 during crystallisation. * Thus, by degrees, a mass of mixed lead 

 and silver is left, extremely rich in the latter. When this richness 

 in silver arrives at the point desired, that metal is extracted in the 

 usual manner by cupellation. The lead-smelting at the Allenhead's 

 mines, and at the Wanlockhead Hills, Dumfriesshire, both excel- 

 lently displayed, are both founded on Pattinson's process. While 

 touching on the Wanlockhead Hills exhibition, we should not 

 pass over the arrangements by which the fumes from the furnace 

 are prevented from escape, and from damage to the surrounding 

 country, while lead, to the amount of thirty-three per cent, from 

 the deposits or " fume'' is obtained. 



3. Plumbago. — The importance of plumbago for the arts and for 

 crucibles is well known. After the Borrowdale mines, Cumber- 

 land, were somewhat exhausted, it became important, for that 

 variety of plumbago employed in arts, to obtain some substitute ; 

 and varieties of compounds were invented, but nothing succeeded 

 so well as the compressing process presented by Mr Brockedon, of 

 which illustrations were in the Exhibition. By this process much 

 of the Borrowdale plumbago dust has been utilised with advan- 

 tage. It, or any other good plumbago, is ground into fine pow- 

 der, placed in packets, and then receives a pressure equal to about 

 5000 tons. To prevent the injurious effect of disseminated air in 

 the packets of fine powder, it is extracted by means of an air- 

 pump, and thus the particles themselves can be brought into close 

 juxtaposition and forced to cohere. Of the application of plumbago 

 to crucibles there were several examples, some well known for their 

 quality. 



II. Professor Owen. 



1. Geology of the Sheep. — The recent progress of palae ontology, 



