CARBON. 303 



tered through charcoal, the whole colouring matter is retained 

 by the latter, and the filtered liquid is colourless. But a so- 

 lution of caustic alkali will divest the charcoal of the blue 

 colouring matter, and carry it away in solution. Other substances 

 also are carried down by animal charcoal, besides animal matters. 

 Lime from lime water, iodine from solution in iodide of potas- 

 sium, soluble subsalts of lead, and metallic oxides dissolved 

 in ammonia and caustic potash ; but it has little or no action 

 upon most neutral salts. The charcoal is apt with time to 

 react upon the substance it carries down, probably from their 

 closeness of contact, reducing the oxide of lead, for instance, 

 in a short time to the metallic state. 



Carbon is chemically the same under all these forms. This 

 element cannot be crystallized artificially by the usual methods 

 of fusion, solution or sublimation, if we except its solution in 

 cast iron, which gives it in the form of graphite and not of 

 the diamond. It is chemically indifferent to most bodies at a 

 low temperature, but combines directly with some metals by 

 fusion and forms carburets. When heated to low redness it 

 burns readily in air or oxygen, forming a gaseous compound 

 carbonic acid, which when cool has exactly the bulk of the 

 original oxygen. With half the proportion of oxygen in car- 

 bonic acid, carbon forms a protoxide, carbonic oxide gas. This 

 gas being supposed similar to steam or to nitrous oxide in its 

 constitution, will be composed of 2 vols. of carbon vapour and 1 

 vol. of oxygen gas condensed into 2 volumes, an assumption 

 upon which the density of carbon vapour, which there are no 

 means of determining experimentally, is usually calculated, and 

 made about 421.5 ; the combining measure of this vapour con- 

 taining 2 volumes (page 132.) It has been inferred from the 

 results of recent organic analysis, that the number 76.44, fixed 

 upon by Berzelius as the equivalent of carbon is too high, and 

 that 75.6 is near the truth.* 



Uses. Several valuable applications of this substance have 

 already been incidentally described. Carbon may be said to 

 surpass all other bodies whatever in its affinity for oxygen at 

 a high temperature ; and being infusible, easily got rid of by 

 combustion, and forming compounds with oxygen which escape 



* By Dr. Clark ; see also Dumas ; Phil. Mag. 3rd. series vol. 14, p. 153, and 

 the account of certain analyses by Mr. Fownes, id, vol 15, p. 62. 



