-iREMACAUSIS OR DECAY. 



.o what happens in combustion at high tem- 

 peratures. It is well known, for example, 

 that when no more oxygen is admitted to a 

 compound of carbon and hydrogen than is 

 sufficient to combine with its hydrogen, the 

 carbon is not turned, but is separated as 

 lamp-black ; while, if the quantity of oxygen 

 is not sufficient even to consume all the hy- 

 drogen, new compounds are formed, such 

 as naphthalin and similar matters, which 

 contain a smaller proportion of hydrogen 

 than those compounds of carbon and hydro- 

 gen which previously existed in the com- 

 bustible substance. 



There is no example of carbon combining 

 directly with oxygen at common tempera- 

 tures, but numerous facts show that hydro- 

 gen, in certain states of condensation, pos- 

 sesses 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 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 re- 

 duction to powder, no trace of carbonic acid I 

 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 there- 

 fore not caused by the oxidation of the car- 

 bon. 



The substances which undergo erema- 

 causis may be divided into two classes. The | 

 first class comprehends those substances i 

 which unite with the oxygen of the air, | 

 without evolving carbonic acid ; and the ! 

 second, such as emit carbonic acid by ab- 

 sorbing oxygen. 



When tne 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 

 anhydrous benzoic acid.* 



* According to the experiments of Dobereiner, 

 100 parts of pyrogallic acid absorbs 38'09 parts of 

 oxygen when in contact with ammonia and water ; 

 the acid being changed in consequence of this ab- 

 sorption into a mouldy substance, which contains 

 less oxygen than the acid itself. It is evident that 

 the substance which is formed is not a higher 

 oxide ; and it is found, on comparing the quantity 

 of the oxvgen absorbed with that of the hydrogen 

 contained in the acid, that they are exactly in the 

 proportions for forming water. 



When colourless orcin is exposed together with 

 ammonia to the contact of oxygen gas, the beau- 

 tiful red-coloured orcein is produced. Now, the 

 only changes which take place here are, that the 

 absorption of oxygen by the elements of orcin 

 and ammonia causes the formation of water ; 1 

 equivalent of orcin CIS H12 08, and 1 equivalent 

 of ammonin NH3, absorb 5 equivalents of oxygen, 

 and 5 equivalents of water are produced, the com- 

 oosition of orcin being C18 HlO O8 N. (Dumas.) 



But, although it appears very probable 

 that the oxygen acts primarily and princi- 

 pally upon hydrogen, the most combustible 

 constituent of organic matter in the state of 

 decay ; still it cannot thence be concluded 

 that the carbon is quite devoid of the power 

 to unite with oxygen, when every particle 

 of it is surrounded with hydrogen, an ele- 

 ment with which the oxygen combines with 

 greater facility. 



We know, on the contrary, that although 

 nitrogen cannot be made to combine witn 

 oxygen directly, yet it is oxidized and forms 

 nitric acid, when mixed with a large quan- 

 tity of hydrogen, and burned in oxygen gas. 

 In this case its affinity is evidently increased 

 by the combustion of the hydrogen, which 

 is in fact communicated to it. It is con- 

 ceivable, that in a similar manner, the car- 

 bon may be directly oxidised in several cases, 

 obtaining from its contact with hydrogen in 

 eremacausis a property which it does not 

 itself possess at common temperatures. But 

 the formation of carbonic acid during the 

 eremacausis of bodies containing hydrogen, 

 must in most cases be ascribed to another 

 cause. It appears to be formed in a man- 

 ner similar to the formation of acetic acid, 

 by the eremacausis of saliculite of potash.* 



An alkaline solution of haematin being 

 exposed to an atmosphere of oxygen, 0-2 

 grm. absorb 28'6 cubic centimetres of oxy- 

 gen gas in twenty-four hours, the alkali ac 

 quiring at the same time 6 cubic centimetres 

 of carbonic acid. (Chevreul.) But these 

 6 cubic centimetres of carbonic acid contain 

 only an equal volume of oxygen, so that il 

 is certain from this experiment that $ of the 

 oxygen absorbed have not united with the 

 carbon. It is highly probable, that during 

 the oxidation of the hydrogen, a portion of 

 the carbon had united with the oxygen con- 

 tained in the haematin, and had separated 

 from the other elements as carbonic acid. 



The experiments of De Saussure upon 

 the decay of woody fibre show that such a 

 separation is quite possible. Moist woody 

 fibre evolved one volume of carbonic acid 

 for every volume of oxygen which it ab- 

 sorbed. It has just been mentioned that 

 carbonic acid contains its own volume of 

 oxygen. Now, woody fibre contains carbon 

 and the elements of water, so that the result 

 of the action of oxygen upon it is exactly 

 the same as if pure charcoal had combined 

 directly with oxygen. But the characters 

 of woody fibre show, that the elements of 

 water are not contained in it in the form of 

 water; for, were this the case, starch, sugar, 

 and gum must also be considered as hydrates 

 of carbon. 



In this case it is evident, that the oxygen absorbed 

 has united merely with the hydrogen. 



* This salt, when exposed to a moist atmo- 

 sphere, absorbs 3 atoms of oxygen ; melanic acid 

 is produced, a body resembling humus, in conse- 

 quence of the formation of which, the elements 

 of 1 atom of acetic acid are separated from the 

 saliculous acid. 



