870 Transactions of the American Institute. 



dale mineral. Long before the final exhaustion of that mine, pro- 

 cesses were invented for cleaning and refining the impure refuse 

 which had been cast away, and improving coarser and less valuable 

 minerals by its use. 



In this way, although the Borrowdale lead could not be had in its 

 palmy days for less than ten dollars, gold, per pound, many manu- 

 facturers could obtain fair material for ten cents per pound. It was, 

 therefore, well worth while to excite the ingenuity of men of science 

 to discover either some equally valuable mines, or, in default thereof, 

 a process whereby the foreign matter could be separated from inferior 

 grapliite, and an absolutely pure product obtained in every respect 

 fit for pencils and crucibles. 



It is, however, a remarkable fact that the Borrowdale graphite 

 owed its fine quality rather to its peculiar state of aggregation than 

 to its purity, as it was ascertained to contain more foreign matter 

 than Ceylon and Canadian graphites. The attempts to refine and 

 clear the impure graphite were carried on by the English mechanics, 

 Brodie and Broekedon, who contrived methods of overcoming the 

 difiiculties of the case. Broekedon was long occupied to render the 

 powdered graphite coherent, by submitting it to enormous pressure, 

 and in 1851 I had occasion to examine his whole apparatus in the 

 London Exhibition. It operated in vacuo, and the difficulty of intro- 

 ducing apparatus under the receiver of an air-pump was avoided by 

 an arrangement of simple character. The powdered graphite was 

 compacted by moderate pressure, and inclosed in very thin paper, 

 wliicli was glued over the whole surface, except a small hole for the 

 air to escape from within. The block thus prepared was placed under 

 an exhausting receiver, the air removed, and the orifice closed with a 

 small piece of paper ; and in this state it was left for twenty-four hours. 

 It was then submitted to a regulated pressure once more ; the difierent 

 particles became agglomerated, and a black graphite was produced 

 as solid as the natural mineral. I examined the specimens exhibited 

 by Mr. Broekedon in the exhibition. They consisted of various 

 gra^jhites from Cumberland, East Indies, Greenland, Spain, Bohemia, 

 and many other localities ; compressed powdered graphite ; powdered 

 graphite prepared in a block, by the process mentioned, and the 

 graphite in small solid cylinders, for Mooday's pencil cases and other 

 drawing pencils. 



Many other methods were devised, by adding various ingredients, 

 intended to be combined with the powdered graphite, without 



