Proceedings of the Polytechnic Association. 869 



3. Graphite is valuable as a lubricator, to prevent friction in 

 machinery, the journals of engines, etc. 



4. To impart lustre to iron, especially for stoves. 



5. In the process of electrotyping or depositing metals by galvan- 

 ism, this material is useful to coat the wax of the moulds, and render 

 it a conductor of the electric current. 



6. In the manufacture of green glass wine bottles, called hock 

 bottles. 



T. In the manufacture of gunpowder, for glazing the grains. 



8. For ''facing" in iron founderies. 



9. For lubricating the action in piano-fortes. 



Tliese are the principal uses made of plumbago in the arts. 



It is well known that the first traces of drawings in lead are con- 

 temporaneous with the earliest development of modern art. Men- 

 tion is made in the fourteenth and fifteen centuries of the use by 

 masters of a pencil-like instrument, on paper surfaced with chalk. 

 This was called the silver drawing. Later, smooth boards, covered 

 with a preparation of calcined bone-dust, were emplo)'ed in place of 

 chalked paper. The Italians made a pencil of metallic, lead, and 

 tin, which they called a stile^ and with that instrument " Petrarch's 

 Laura," a portrait from life, is known to have been executed ; while 

 Michael Angelo is said to have made use of the instrument in the 

 sixteenth century. Vasari speaks of the advantages that artist 

 derived from the stile, the quill, and both black and red chalk. 



The discovery of the Borrowdale mine, in Cumberland, dispelled 

 all other contrivances for writing, and the manufacture of lead pen- 

 cils became quite universal. Tlie mineral, as it came from the mine, 

 was sawed into thin slabs, and these again into long strips of the 

 requisite size, which were, without further preparation, glued into 

 the wood. These pencils are not surpassed in delicacy or smoothness, 

 and to this day are made in the same manner as they were 300 years 

 ago. The black lead mine at Borrowdale had a yearly revenue of 

 £40,000, sterling, from the montlily public sales. The mine was 

 only allowed to be open six weeks in a year, that the market might 

 not be overstocked. This great mine is now exhausted, and nothing 

 but impure refuse is obtained from that celebrated locality. Eng- 

 lish manufiicturers and men of science have been searching for new 

 supplies, hut the discoveries in Spain, Ceylon, Greenland, California, 

 France, Italy, Canada, and the Atlantic States, made from time to 

 time, have not yet produced a complete substitute for the Borrow- 



