OXYGEN. 25 1 



the proportion of oxygen consumed, for the greater the weight 

 of oxygen with which a pound of any combustible unites, the 

 more heat is produced. The following results indicate that 

 the heat depends exclusively upon the oxygen consumed, four 

 different combustibles in consuming a pound of oxygen afford- 

 ing nearly the same quantity of heat : 



HEAT FROM COMBUSTION. 



1 pound of oxygen with hydrogen heats from 32 to 212, 29 Ibs. of water, 

 i, with charcoal 29 



with alcohol 28 



with ether 28J 



The quantity of combustible consumed in these experiments 

 varied considerably, but the oxygen being the same, the heat 

 evolved was nearly the same also. But when the same quan- 

 tity of oxygen converted phosphorus into phosphoric acid, 

 exactly twice as much heat was evolved, according to Despretz, 

 as in the former experiments. It is doubtful whether these 

 observations will lead to any general conclusions; but it is 

 certain that the coincidences which they exhibit merit atten- 

 tion. The superior vivacity of the combustion of these and 

 other bodies in pure oxygen, compared with air, depends en- 

 tirely upon the increased rapidity of the process, and the larger 

 quantity of combustible oxidated in a given time. A candle 

 burns with more light and heat in oxygen than in air, but it 

 consumes proportionally faster. 



Oxidation is often a very slow process and imperceptible in 

 its progress, as in the rusting of iron and tarnishing of lead 

 exposed to the atmosphere. The heat being then evolved in 

 a very gradual manner is dissipated and never accumulates. 

 But when the oxide formed is the same, the nature of the 

 change effected is no way altered by its slowness. Iron oxi- 

 dates rapidly when introduced in a state of ignition into oxygen 

 gas, and lead, in the form of the lead pyrophorus, which con- 

 tains that metal in a state of high division, takes fire sponta- 

 neously and burns in the air, circumstances then favouring the 

 rapid progress of oxidation. 



Oxidation may also go on with a degree of rapidity sufficient 

 to occasion a sensible evolution of heat, but without flame and 

 open combustion. The absorption of oxygen by spirituous liquors 

 in becoming acetic acid, and by many other organic substances, 



