EXAMPLES OF. 397 



portion 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 condensation, possesses that property. Lamp- 

 black which has been heated to redness may be kept in contact 

 with oxygen gas, without forming carbonic acid ; but lamp-black, 

 impregnated with oils containing 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 con- 

 tained in it 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 matters subject to eremacausis may be divided into two 

 classes. The first class comprehends those substances which 

 unite with the oxygen of the air, without evolving carbonic acid ; 

 and the second, such as emit carbonic acid while they absorb 

 oxygen. 



When the oil of bitter almonds is exposed to the air, it absorbs 

 two equivalents of oxygen, and is converted into benzoic acid ; 

 but half of the oxygen absorbed combines with the hydrogen of 

 the oil, and forms water, which remains in union with the anhy- 

 drous benzoic acid. 



According to the experiments of Dobereiner, 100 parts of 

 pyrogallic acid absorb 38*09 parts of oxygen when in contact 

 with ammonia and water ; the acid being changed in conse- 

 quence of this absorption into a mouldy substance, which contains 

 less oxygen than the acid itself. It is evident that the substance 

 formed is not a higher oxide ; and it is found, on comparing the 

 quantity of the oxygen absorbed with that of the hydrogen con- 

 tained in the acid, that they are exactly in the proportions for 

 forming water. 



When colorless orcin is exposed together with ammonia to tho 

 contact of oxygen gas, the beautiful red-colored orcein is produc- 

 14* 



