OXYGEN. 249 



to maintain the animal heat in part. A small animal, also, such 

 as a mouse or bird, lives four or five times longer in a vessel of 

 oxygen than it will in an equal bulk of air. But the continued 

 respiration of this gas in a state of purity is injurious to animal 

 life. A rabbit is found to breathe it without inconvenience for 

 some time, but after an interval of an hour or more, the circu- 

 lation and respiration are much quickened ; and a state of 

 great excitement of the general system supervenes ; this is by 

 and by followed by debility, and death occurs in from six to 

 ten hours. The blood is found to be highly florid in the veins 

 as well as the arteries, and the heart, according to Broughton, 

 continues to act strongly after the breathing has ceased. 



Oxygen may be made to unite with all the other elements 

 except fluorine, and forms oxides, while the process of uniting 

 with oxygen is termed oxidation. With the same element 

 oxygen often unites in several proportions, forming a series of 

 oxides, which are then distinguished from each other by the 

 different prefixes enumerated under chemical nomenclature 

 (page 98.) Many of its compounds are acids, particularly 

 those which contain more than one equivalent of oxygen to 

 one of the other element, and compounds of this nature are 

 those which it most readily forms with the non-metallic ele- 

 ments, such as carbonic acid with carbon, sulphurous acid with 

 sulphur, phosphoric acid with phosphorus. But oxygen unites 

 in preference with single equivalents of a large proportion of 

 the metallic class of elements,, and forms bodies which are 

 alkaline or have the character of bases, such as potash, lime, 

 magnesia, protoxide of iron, &c. A certain number of its 

 compounds are neither acid nor alkaline, and are therefore 

 called neutral bodies, such as the oxide of hydrogen or water, 

 carbonic oxide, and nitrous oxide. The greater number of 

 these neutral oxides are also protoxides. 



It has already been stated that in a classification of the 

 elements oxygen does not stand alone, but forms one of a small 

 natural family along with sulphur, selenium and tellurium 

 (page 142.) These elements also form acid, basic and neutral 

 classes of compounds, with the same bodies as oxygen does, 

 of which the sulphur compounds are well known, and always 

 exhibit a well-marked analogy to the corresponding oxides. 

 Oxygen acids unite with oxygen bases, and form neutral salts, 

 so do sulphur acids with sulphur bases, selenium acids 



