CARBON AND THE HYDROCARBONS 851 



Becomes strongly incandescent, partially volatilises, and is deposited in 

 the form of graphite. If sugar be placed in a charcoal crucible and 

 a powerful galvanic current passed through J;, it is baked into a mass 

 similar to graphite. If charcoal be mixed with wrought iron and 

 heated, cast iron is formed, which contains as much as five per cent, of 

 charcoal. If molten cast iron be suddenly chilled, the carbon remains 

 in combination with the iron, forming so called white cast iron ; but if 

 the cooling proceeds slowly, the greater part of the carbon separates 

 in the form of graphite, and if such cast iron (so called grey cast 

 iron) be dissolved in acid, the carbon remains in the form of graphite. 

 Graphite is met with in nature, sometimes in the form of large com- 

 pact masses, sometimes permeating rocky formations like the schists 

 or slates, and in fact is met with in those places which, in all proba- 

 bility, have been subjected to the action of subterranean heat. 14 The 

 graphite in cast iron, and sometimes also natural graphite, occasionally 

 appears in a crystalline form in the shape of six-sided plates, but more 

 often it occurs as a compact amorphous mass having the characteristic 

 properties of the familiar black-lead pencil. 15 



The diamond is a crystalline and transparent form of carbon. It is 



1 ' There are places where anthracite" gradually changes into graphite as the strata 

 sink. I myself had the opportunity of observing this gradual transformation in the 

 valley of Aosta. 



15 Pencils are made of graphite worked up into a homogeneous mass by disintegra- 

 ting, powdering, and cleansing it from earthy impurities ; the best kinds are made of 

 -completely homogeneous graphite sawn up into the requisite sticks. Graphite is found 

 in many places. In Russia the so-called Aliberoffsky graphite is particularly renowned ; 

 it is found in the Altai mountains near the Chinese frontier ; in many places in Finland 

 and likewise on the banks of the Little Tungouska, Sidoroff also found a considerable 

 quantity of graphite. When mixed with clay, graphite is used for making crucibles and 

 pots for melting metals. 



Graphite, like most forms of charcoal, still contains a certain quantity of hydrogen, 

 oxygen, and ash, so that in its natural state it does not contain more than 98 p.c. of 

 carbon. 



In practice, graphite is purified simply by washing it when in a finely-ground state, 

 by which means the bulk of the earthy matter may be separated. The following process, 

 proposed by Brodie, consists in mixing the powdered graphite with -fa part of its weight 

 of potassium chlorate. The mixture is then heated with twice its weight of strong 

 sulphuric acid until no more odoriferous gases are emitted ; on cooling, the mixture is 

 thrown into water and washed ; the graphite is then dried and heated to a red heat ; 

 after this it shrinks considerably in volume and forms a very fine powder, which is 

 then washed. By acting on graphite several times with a mixture of potassium chlorate 

 and nitric acid heated up to 60, Brodie transformed it into a yellow insoluble acid 

 substance which he called graphitic acid, C n H 4 O 5 . The diamond remains unchanged 

 when subjected to this treatment, whilst amorphous charcoal is completely oxidised. 

 Availing himself of this possibility of distinguishing graphite from the diamond or amor- 

 phous charcoal, Berthelot showed that when compounds of carbon and hydrogen are 

 decomposed by heat, amorphous charcoal is mainly formed, whilst when compounds of 

 carbon with chlorine, sulphur, and boron are decomposed, graphite is principally 

 deposited. 



