262 EREMACAUSIS OR DECAY. 



Many bodies which do not decay when moistened 

 with water, enter into eremacausis when in contact 

 with an alkali. Gallic acid, haematin, and many 

 other compounds, may be dissolved in water and 

 yet remain unaltered, but if the smallest quantity of 

 a free alkali is present, they acquire the property of 

 attracting oxygen, and are converted into a brown 

 substance like humus, evolving very frequently at 

 the same time carbonic acid. (Chevreul.) 



A very remarkable kind of eremacausis takes 

 place in many vegetable substances, when they are 

 exposed to the influence of air, water, and ammonia. 

 They absorb oxygen very rapidly, and form splendid 

 violet or red-coloured liquids, as in the case of orcin 

 and erythrin. They now contain an azotised sub- 

 stance, not in the form of ammonia. 



All these facts show that the action of oxygen 

 seldom affects the carbon of decaying substances, 

 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 suf- 

 ficient to combine with its hydrogen, the carbon is 

 not burned, but is separated as lamp-black ; while, 

 if the quantity of oxygen is not sufficient even to 

 consume all the hydrogen, new compounds are 

 formed, such as naphthalin and similar matters, 

 which contain a smaller proportion of hydrogen than 

 those compounds of carbon and hydrogen which 

 previously existed in the combustible substance. 



