CONDITIONS FOR ITS OCCURRENCE. 261 



When vegetable juices are evaporated by a gentle 

 heat in the air, a brown or brownish-black sub- 

 stance is precipitated as a product of the action of 

 oxygen upon them. This substance, which appears 

 to possess similar properties from whatever juice it 

 is obtained, has received the name of extractive 

 matter; it is insoluble or very sparingly soluble in 

 water, but is dissolved with facility by alkalies. By 

 the action of air on solid animal or vegetable mat- 

 ters, a similar pulverulent brown substance is 

 formed, and is known by the name of humus. 

 (Terreau.) 



The conditions which determine the commence- 

 ment of eremacausis are of various kinds. Many 

 organic substances, particularly such as are mix- 

 tures of several more simple matters, oxidise in the 

 air when simply moistened with water ; others not 

 until they are subjected to the action of alkalies ; 

 but the greatest part of them undergo this state 

 of slow combustion or oxidation, when brought in 

 contact with other decaying matters. 



The eremacausis of an organic matter is retarded 

 or completely arrested by all those substances 

 which prevent fermentation or putrefaction. Min- 

 eral acids, salts of mercury, aromatic substances, 

 empyreumatic oils, and oil of turpentine, possess 

 a similar action in this respect. The latter sub- 

 stances have the same effect on decaying bodies 

 as on phosphuretted hydrogen, the spontaneous 

 inflammability of which they destroy. 



