238 CONSIDERATION OF CARBON COMPOUNDS. 



and a greater variety of compounds than would be the case if 

 they were elements of equal valence and of similar properties. 



General properties of organic compounds. The substances 

 formed by the union of the four elements just mentioned have 

 properties in some respects intermediate to those of their com- 

 ponents. Thus, no organic substance is either permanently 

 solid 1 like carbon, nor an almost permanent gas like hydrogen, 

 oxygen, and nitrogen. 



Some organic substances are solids, others liquids, others 

 gases; they are generally solids when the carbon atoms pre- 

 dominate; they are liquids or gases when the gaseous elements, 

 and especially hydrogen, predominate; likewise, it may also be 

 said that compounds containing a small number of atoms in the 

 molecule are gases or liquids which are easily volatilized ; they 

 are liquids of high boiling-points, or solids, when the number 

 of atoms forming the molecules is large. 



The combustible property of carbon and hydrogen is trans- 

 ferred to all organic substances, every one of which will burn 

 when sufficiently heated in atmospheric air. (If carbon di- 

 oxide, carbonic acid and its salts, be considered organic com- 

 pounds, we have an exception to the rule, as they are not com- 

 bustible.) 



The properties possessed by organic compounds are many and 

 widely different. There are organic acids, organic bases, and 

 organic neutral substances ; there are some organic compounds 

 which are perfectly colorless, tasteless, and odorless, whilst 

 others show every possible variety of color, taste, and odor; 

 many serve as food, whilst others are most poisonous ; in short, 

 organic substances show a greater variety of properties than the 

 combinations formed by any four other elements. 



And yet, the cause of all the boundless variety of organic 

 matter is that peculiar attraction called chemical affinity, acting 

 between the atoms of a comparatively small number of ele- 

 ments and uniting them in many thousand different propor- 

 tions. 



1 Non-volatile organic substances are decomposed by heat with generation of 

 volatile products. 



