252 ME. JOHN LEIGH ON THE CHEMICAL CHANGES 



varieties) is composed of 24 atoms carbon, 13 atoms hydro- 

 gen, and 1 atom oxygen, and 36 : 22 : : 24 : 14, so that the 

 hydrogen exists in a slightly less relative proportion in 

 cannel coal than in vrood. 



Every organized body, every organism, though not every 

 body of organic origin — every plant and animal — essentially 

 consists of four elements; hence often called organic ele- 

 ments — carbon, oxygen, hydrogen, and nitrogen. To these 

 are superadded certain mineral substances also necessary to 

 the existence of an organized body, forming, in fact, the 

 skeleton o{ the plant or animal, and which, on the combus- 

 tion of the body, are left as its ashes. The chief of these 

 mineral ingredients are carbonate, sulphate, and phosphate 

 of lime, to which may be added, in smaller proportion, 

 compounds of potass, soda, magnesia, iron, and manganese. 



When an organized body perishes, and decomposes with 

 free access of air, as in the open atmosphere, its organic 

 elements are converted into carbonic acid, water, and am- 

 monia, the oxygen of the air assisting in the formation of 

 the two former; these form the food and pabulum of a new 

 vegetable existence, a constant cycle taking place of reno- 

 vation and decay. It is manifest that, by the assistance of 

 the atmospheric oxygen, the hydrogen and carbon are more 

 rapidly and completely removed than when they are covered 

 up. The composition of oak wood, which had been treated 

 with water, alcohol, ether, diluted acids, and diluted alkalies 

 in succession, to remove all extraneous matters but the woody 

 fibre, was found, as stated above, to be — carbon 36 atoms, 

 hydrogen 22 atoms, oxygen 22 atoms. The pure ligneous 

 structure found within the cells of plants, was found to be 

 composed of carbon 36, hydrogen 24, oxygen 24. Now, as 

 water is a compound of 1 atom of hydrogen and 1 atom 

 oxygen, the forms of vegetable matter may be regarded in 

 the light of compounds of carbon with variable proportions 

 of water ; oak wood being a compound of 36 atoms of car- 



