442 CONSIDERATION OF CARBON COMPOUNDS. 



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 many 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 

 inorganic substances, in so far as the qualitative examination of an 

 organic substance furnishes in many cases but little proof of the true 

 nature of the substance (except that it is organic), while the quali- 

 tative analysis of an inorganic substance discloses in most cases the 

 true nature of the substance at once. 



For instance : If a white, solid substance, upon examination, be 

 found to contain potassium and iodine, and nothing else, the conclu- 

 sion may at once be drawn that the compound is potassium iodide, 

 containing 38.86 parts by weight of potassium, and 125.9 parts by 

 weight of iodine. Or, if another substance be examined, and found 

 to be composed of mercury and chlorine, the conclusion may be drawn 

 that the compound is either mercurous or mercuric chloride, as no 

 other compounds containing these two elements are known, and 

 whether the examined substance be the lower or higher chloride of 

 mercury, or a mixture of both, can easily be determined by a few 

 simple tests. 



While thus the qualitative examination discloses the nature of the 

 substance, it is different with organic compounds. Many thousand 

 times the analysis might show carbon, hydrogen, and oxygen to be 

 present, and yet every one of the compounds examined might be 

 entirely different ; it is consequently not only the quality of the ele- 

 ments, but chiefly the quantity present which determines the nature 

 of an organic substance, and in order to identify an organic substance 

 with certainty, it frequently becomes necessary to make a quantitative 

 determination of the various elements present, and this quantitative 

 analysis is generally called ultimate or elementary analysis. 



