280 CONSIDERATION OF CARBON COMPOUNDS. 



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), whilst 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 39 parts by weight of potassium, and 126.5 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. 



Whilst 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 by which the elements in organic substances are determined 

 is generally called ultimate or elementary analysis. 



There are, however, for many organic substances such character- 

 istic tests that these substances may be recognized by them ; these 

 reactions will be mentioned in the proper places. 



An analysis by which different organic substances, when mixed 

 together, are separated from each other is frequently termed proximate 

 analysis. Such an analysis includes the separation and determination 

 of essential oils, fats, alcohols, sugars, resins, organic acids, albuminous 

 substances, etc., and is one of the most difficult branches of analytical 

 chemistry. 



Qualitative analysis of organic substances. The presence of 

 carbon in a combustible form is decisive in regard to the organic 

 nature of a compound. If, consequently, a substance burns with 

 generation of carbon dioxide (which maybe identified bypassing the 



