CAEBON AND THE HYDROCARBONS 839' 



into combination in molecules of its compounds ; but the weight of 

 the molecules of charcoal is probably very much greater. This weight 

 remains unknown because charcoal is capable of but few direct 

 reactions and those only at a high temperature (when the weight 

 of its molecules probably changes, as when ozone changes into oxygen), 

 and it does not turn into vapour. Carbon exists in nature, both in 

 a free and combined state, in most varied forms and aspects. Carbon 

 in a free state is found in at least three different forms, as charcoal, 

 graphite, and the diamond. In a combined state it enters into the 

 composition of what are called organic substances a multitude of 

 substances which are found in all plants and animals. It exists 

 as carbonic anhydride both in air and in water, and in the soil 

 and crust of the earth as salts of carbonic acid and as organic 

 remains. 



The variety of the substances of which the structure of plants and 

 animals is built up is familiar to all. Wax, oil, turpentine, and tar, 

 cotton and albumin, the tissue of plants and the muscular fibre of 

 animals, vinegar and starch, are all vegetable and animal matters, and 

 all carbon compounds. 1 The class of carbon compounds is so vast 



1 Wood is the non-vital part of ligneous plants : the vital part of ordinary trees is 

 situated between the bark and the lignin. Every year a layer of lignin is deposited on 

 this part by the juices which are absorbed by the roots and drawn up by the leaves ; for 

 this reason the age of trees may be determined by the number of lignin layers deposited. 

 The woody matter consists principally of fibrous tissue on to which the lignin or so-called 

 incrusting matter has been deposited. The tissue has the composition C 6 H 10 O 5 , the 

 substance deposited on it contains more carbon and hydrogen and less oxygen. This 

 matter is saturated with moisture when the wood is in a fresh state. Fresh birch wood 

 contains about 81 p.c. of water, lime wood 47 p.c., oak 85 p.c., pine and fir about 37 p.c. 

 When dried in the air the wood loses a considerable quantity of water and not more than 

 19 p.c. remains. By artificial means this loss of water may be increased. If water be driven 

 into the pores of wood the latter becomes heavier than water, as the tignin of which it is 

 composed has a density of about 1*6. One cubic centimetre of birch wood does not 

 weigh more than 0'901 gram, fir 0-894, lime tree 0'817, poplar '765 when in a fresh 

 state ; when in a dry state birch weighs 0'622, pine 0'550, fir 0'355, lime 0'430, guaiacuin 

 1-842, ebony 1-226. On one hectare (2'7 acres) of woodland the yearly growth averages 

 the amount of 8,000 kilograms (or about 8 tons) of wood, but rarely reaches as much as 

 6,000 kilos. The average chemical composition of wood dried in air may be expressed as 

 follows : Hygroscopic water 15 p.c., carbon 42 p.c., hydrogen 5 p.c., oxygen and nitrogen 

 87 p.c., ash 1 p.c. Wood parts with its hygroscopic water at 150, and decomposes at 

 about 800, giving a brown, brittle, so-called red charcoal ; above 350 black charcoal is 

 produced. As the hydrogen contained in wood requires for its combustion about forty parts 

 by weight of oxygen, which is present to the amount of about 86 p.c., all that burns of 

 the wood is the carbon which it contains, 100 parts of wood only giving out as much heat 

 as forty parts of charcoal, and therefore it would be far more profitable to use charcoal for 

 heating purposes than wood, if it were possible to obtain it in such quantities as corre- 

 spond with its percentage ratio that is forty parts per 100 parts of wood. Generally, 

 however, the quantity produced is far less, not more than 80 p.c., because part of the 

 carbon is given oil aa gas, tar, &c. If wood has to be transported great distances, or if 



