INTRODUCTORY REMARKS. 279 



Thus, no organic substance is either permanently solid l 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 predominate ; they 

 are liquids or gases when the gaseous elements, and especially hydro- 

 gen, predominate ; likewise, it may also be said that compounds con- 

 taining 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 transferred 

 to all organic substances, every one of which will burn when suffi- 

 ciently heated in atmospheric air. (If carbon dioxide, carbonic acid 

 and its salts be considered organic compounds, we have an exception 

 to the rule, as they are not combustible.) 



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 other 

 four 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 elements and uniting them 

 in many thousand different proportions. 



It would, of course, be entirely inconsistent with the object of this 

 book, if all the thousands of organic substances already known (the 

 number of which is continually being increased by new discoveries) 

 were to be considered, or even mentioned. It must be sufficient to 

 state the general properties of the various groups of organic sub- 

 stances, to show by what processes they are produced artificially or 

 how they are found in nature, how they may be recognized and 

 separated, and, finally, to point out those members of each group 

 which claim a special attention for one reason or another. 



Difference in the analysis of organic and inorganic sub- 

 stances. The analysis of organic substances differs from that of 



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

 products. 



