CABB03 AND THE HYDROCARBONS 339 



(t// t ,fr(rj>i>' /ni'iiia. The two particular forms in which carbon appears 

 arc t lie tlinHinnil and f/r<i/i/i iff. The identity of the composition of these 

 with charcoal is proved by burning an equal quantity of all three 

 separately in oxygen (at a great heat), when each gives the same 

 quantity of carbonic anhydride -namely, 12 parts of charcoal, diamond, 

 or graphite in a pure state, yield on burning 44 parts by weight of 

 carbonic anhydride. The physical properties present a marked con- 

 trast ; the densest sorts of charcoal have a density of only 1-9, whilst 

 the density of graphite is about 2-3, and that of the diamond 3'5. A 

 great many other properties depend on the density, for instance, com 

 bustibility. The lighter charcoal is, the more easily it burns ; graphite 

 burns with considerable difficulty even in oxygen, and the diamond 

 burns only in oxygen and at a very high temperature. On burning, 

 charcoal, the diamond, and graphite develop different quantities of heat. 

 One part by weight of wood charcoal converted by burning into 

 carbonic anhydride develops 8080 heat units :. dense charcoal 

 separated in gas retorts develops 8050 heat units ; natural graphite, 

 7*00 heat units ; and the diamond, 7770. The greater the density 

 the less the heat evolved by the combustion of the carbon. 13 



By means of intense heat charcoal may be transformed into 

 graphite. If a charcoal rod 4mm. in diameter and 5mm. long be enclosed 

 in an exhausted receiver and the current from 600 Bunsen's elements, 

 placed in parallel series of 100, be passed through it, the charcoal 

 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 it, it is baked into a mass 

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

 heated, cast iron is formed, which absorbs 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 

 compact masses, sometimes it permeates rocky formations like the 

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



'" When subjected to pressure, charcoal loses heat, hence the densest form stands to 

 the less druse as a solid to a liquid, or as a compound to an element. From this the 

 conclusion mi>jht be drawn, that the molecules of graphite are more complex than those 

 of charcoal, and those of the diamond still more so. The specific heat shows the same 

 tiling, because, as we shall see on further exposition, the complexity of a molecule leads 

 to a diminution of the specific heat. At ordinary temperatures, the specific heat of 

 charcoal is 0"24, graphite 0*20, the diamond 0'147. 



z 2 



