324 EREMACAUSIS OR DECAY, 



and this corresponds exactly to what happens in 

 combustion at high temperatures. It is well known, 

 for example, that when no more oxygen is admitted 

 to a compound of carbon and hydrogen than is suffi- 

 cient to combine with its hydrogen, the carbon is not 

 burned, but is separated as lampblack;* while, if 

 the quautity of oxygen is not sufficient even to con- 

 sume all the hydrogen, new compounds' are formed, 

 such as napthalinf and similar matters, which con- 

 tain a smaller proportion of hydrogen than those 

 compounds of carbon and hydrogen which previously 

 existed in the combustible substance. 



There is no example of carbon combining directly 

 with oxygen at common temperatures, but numerous 

 facts show that hydrogen, in certain states of con- 

 densation, possesses that property. Lampblack which 

 has been heated to redness may be kept in contact 

 with oxygen gas, without forming carbonic acid; 

 but lampblack, impregnated with oils which contain 

 a large proportion of hydrogen, gradually becomes 

 warm, and inflames spontaneously. The spontaneous 

 inflammability of the charcoal used in the fabrication 

 of gunpowder has been correctly ascribed to the 

 hydrogen, which it contains in considerable quantity; 

 for during its reduction to powder, no trace of 

 carbonic acid can be detected in the air surrounding 

 it ; it is not formed until the temperature of the mass 

 has reached a red heat. The heat which produces 

 the inflammation is, therefore, not caused by the 

 oxidation of the carbon. 



The substances which undergo eremacausis may 

 be divided into two classes. The first class compre- 

 hends those substances which unite with the oxygen 

 of the air, without evolving carbonic acid ; and the 

 second, such as emit carbonic acid by absorbing 

 oxygen. 



When the oil of bitter almonds is exposed to the 



* As in the combustion of spirits of turpentine, now much employed, 

 under various names, in lamps. 



t A substance obtained from coal tar. 



