Changes in the lungs produced by natural graphite.

Graphite or plumbago is a crystalline form of carbon which occurs in nature as soft black masses or, less commonly, as crystals in igneous rocks: this natural graphite contains varying proportions of other minerals. Graphite is also made artificially from coke, and the best preparations of this kind are nearly pure carbon. This paper will deal with some of the effects of natural graphite, and the term " graphite " will be used to mean " natural graphite," that is, a mixture of minerals, largely crystalline carbon. The main sources of graphite in 1935 were the U.S.S.R. 39 per cent., Korea 21 per cent., Germany 10 per cent., Austria 9 per cent., Ceylon 7 per cent., Madagascar 5 per cent., and Mexico 3 per cent. (Jones, 1943). During recent years the graphite used in Great Britain has come mainly from Ceylon and South-west Africa, but there has also been a small quantity mined in Borrowdale, Cumberland. Not much more than 10 per cent. of the graphite produced in the world is used in pencils and crayons; more than half of it is employed in foundries and in making crucibles for metallurgical purposes. Finely ground graphite is used extensively as a lubricant, either alone or in combination with oil or grease: considerable quantities of the poorer quality graphite are used in paints and pigments for protecting metallic surfaces from various corroding substances-for example, stove polish, which consists of graphite mixed with some amorphous carbon and a little grease. Graphite is also used for making electrodes and dynamo brushes, and in dry batteries. For most purposes graphite has to be ground to a fine powder, and there is a small industry devoted to grinding graphite which it supplies to commercial users. In other cases the grinding is done as a