No. 31.-1885.] 



PLUMBAGO. 



197 



German city began the manufacture of pencils with 

 pulverized graphite cemented into solid blocks by means 

 of gums and similar substances ; but useful pencils in 

 quantity were manufactured only after Conte of Paris 

 in 1795 devised the process by which now all black lead 

 pencils, and indeed pencils of all sorts, are manufactured. 

 As will be seen subsequently, this is the process adopted in 

 The Joseph Dixon Works in America, and the writer in the 

 Encyclopaedia Britannica, from whose article I am quoting, 

 asserts that the Conte method has, now that even dust 

 cannot be obtained from Borrowdale, quite superseded 

 the processes patented by Mr. Brockendon in 1843, of 

 subjecting pure graphite to enormous pressure and air 

 exhaustion. 



In the Conte process graphite and clay are first and 

 separately brought to a condition of the finest subdivision, 

 the graphite being calcined to a bright red heat. The par- 

 ticles of each mineral are then floated from one vat of water 

 to another, the finest particles last to sink being of course 

 used to make the finest pencils. The minerals are then 

 thoroughly incorporated, ground together (that is the 

 various qualities), placed in bags, and squeezed in a hydraulic 

 press to the consistency of dough. The mass is then forced 

 through apertures, taking the shape of pencil rods, and 

 being finally subjected to more or less furnace heat as hard 

 or soft qualities are desiderated. The prepared " rods" are 

 then put into cedar cases, on which quality is indicated by 

 letters, such as " B" for black ; " H" for hard ; " S. T." for 

 soft streak, &c. Black lead pencils of an inferior quality 

 are made from graphite dust mixed with melted sulphur and 

 run into moulds, those used by carpenters being mixed with 

 tallow to give them softness. Coloured pencils are made 

 from appropriate mineral matters mixed with clay. 



The graphite in Borrowdale was found in the primitive 

 rocks in pockets or nests, and so in Ceylon very large masses 

 of pure plumbago, over a quarter of a ton in weight, have 

 been dug out of our crystalline rocks perfectly free from all 

 impurities, with no particles of iron pyrites, gneiss, or of the 

 beautifully white and transparent quartz with which the black 

 mineral is so generally associated. But here, as in India, the 

 United States, Canada, and other countries, graphite is also 



