ORGANIC MATTER. f 



which contains the still higher multiples, is solid. There 



are three compounds of hydrogen and nitrogen that have 

 been obtained in a free state ammonia (N H 3 ) is gaseous, 

 but liquefiable by pressure, or by reducing its temperature 

 to 40 F., and it solidifies at 112 F. ; hydrazine 

 (NH 2 -NH 2 )is liquid at ordinary temperatures, but hydro- 

 zoic acid (N 3 H) has so far only been obtained in the form of 

 a highly explosive gas. In cyanogen, which is composed 



of carbon and nitrogen, (C N) 2 , we have a gas that becomes 

 liquid at a pressure of four atmospheres and solid at 30 F. 

 And in paracyanogen, formed of the same proportions of 

 these elements in higher multiples, we have a solid which does 

 not fuse or volatilize at ordinary temperatures. Lastly, 



in the most important member of this group, water (H 2 0), 

 we have a compound of two difficultly-condensible gases which 

 assumes both the fluid state and the solid state within ordi- 

 nary ranges of temperature; while its molecular mobility 

 is still such that its fluid or solid masses are continually pass- 

 ing into the form of vapour, though not with great rapidity 

 until the temperature is raised to 212. 



Considering them chemically, it is to be remarked of these 

 diatomic compounds of the four chief organic elements, that 

 they are, on the average, less stable than diatomic compounds 

 in general. Water, carbonic oxide, and carbonic acid, are, 

 it is true, difficult to decompose. But omitting these, the 

 usual strength of union among the elements of the above- 

 named substances is low considering the simplicity of the 

 substances. With the exception of acetylene and possibly 

 marsh gas, the various hydro-carbons are not producible 

 by directly combining their elements; and the elements of 

 most of them are readily separable by heat without the aid 

 of any antagonistic affinity. Nitrogen and hydrogen do not 

 unite with each other immediately save under very excep- 

 tional circumstances; and the ammonia which results from 

 their union, though it resists heat, yields to the electric 

 spark. Cyanogen is stable : not being resolved into its com- 



