PROPERTIES OF OXYGEN. 293 



half of the weight of the general crust of the earth. To come 

 to organic nature, it forms half the weight of lignine, which is 

 nearly identical with wood, and nearly a fourth part in the 

 weight of dried muscular flesh. The only simple bodies which 

 approach to the same abundance with oxygen in nature are 

 silicon, the inflammable basis of flint ; and the metal alu- 

 minum, the basis of our clays. The bodies found in nature 

 destitute of oxygen are the few simple bodies found in the 

 uncombined state, such as carbon in the form of diamond, 

 sulphur, and those metals which exist in the virgin state ; also, 

 several compound bodies, such as the native compounds of 

 chlorine, iodine, and sulphur, and therefore the natural beds of 

 rock-salt and the native sulphurets or sulphides of iron, copper, 

 and zinc. 



Oxygen in the uncombined state is known only in the form 

 of gas ; all attempts to condense it into a liquid have hereto- 

 fore failed. It combines with every simple substance hitherto 

 discovered, with the exception of fluorine, which, however, is 

 still a simple body only by hypothesis. It appears to be 

 owing to its energetic affinity for bodies that it supports com- 

 bustion in so high a degree. Oxygen gas, however, hardly 

 sets bodies on fire at ordinary temperatures, as chlorine does. 

 But many bodies which burn tranquilly in atmospheric air 

 that is, in oxygen diluted with about four parts of nitrogen 

 burn vividly when put, in a state of combustion, into oxygen gas. 

 A splinter of wood, with a glowing spark upon it, soon exhausts 

 itself and goes out in atmospheric air ; but if put into oxygen 

 gas, the spark bursts into flame and burns brilliantly. In this 

 case combustion is going on in the air, but the evolution of 

 heat is so slow that less heat is extricated from the spark than 

 is sufficient to compensate for the amount lost from the burn- 

 ing spot by the conduction and radiation of heat therefrom ; 

 whence the heat required for the continuance of the combustion 



