174 DESCRIPTIVE MINERALOGY. 



This gas is sometimes given out by marshes, and is probably formed by the decomposi- 

 tion of animal and vegetable matters. As it is spontaneously inflammable, it has been known 

 by the names Ignis fatuus, Lantern Jack, &c. It is sometimes mixed with carburetted 



hydrogen. 



ORDER II. NON-COMBUSTIBLE GASES. 



Under this order are included 



1. Oxygen. 3. Carbonic acid. 



2. Nitrogen. 4. Atmospheric air. 



OXYGEN. 



[From the Greek ogu.c, an acid, and yewau, I generate; it having been formerly supposed to be essen- 

 tial to acidity.] 



Description. Gaseous, colourless, inodorous, tasteless, and transparent ; sparingly dis- 

 solved by water. It is a powerful supporter of combustion, and is essential to respiration. 

 Specific gravity 1102, water being 1000. 



Burning bodies introduced into this gas burn with greatly increased brilliancy, and even 

 some substances, which are not ordinarily thought to be combustible, when ignited, undergo 

 rapid combustion in it ; as iron wire, steel watch springs, etc. 



This gas is largely evolved from vegetables. The carbonic acid which they absorb is de- 

 composed, the carbon being appropriated to the vegetable and the oxygen given out. In some 

 cases it is said to predominate in the air given out by springs. I have introduced it chiefly 

 for the purpose of directing attention to the subject. 



NITROGEN. 



[So called from its being the basis of nitric acid and nitre.] 

 Nitrogen. Shcpard and Dana. — Azote. Bcudant. 



Description. Gaseous, colourless, transparent, tasteless and inodorous ; it is absorbed by 

 water only in very small quantity. It is lighter than atmospheric air, its specific gravity being 

 976, compared to air as 1000. It does not support combustion nor animal life, and is indeed 

 characterized by the absence of those properties which distinguish the other gases. 



