312 CHEMISTRY. 



briefly how chemists determine the constitution of organic 

 bodies. There are two kinds of organic analysis : first, proxi- 

 mate analysis separates the several definite compounds or 

 proximate elements of which a complex substance is com- 

 posed ; second, ultimate analysis determines the number of 

 atoms of the elementary bodies in the molecule of & proxi- 

 mate constituent. For example, starch, cellulose, gluten, 

 sugar, coloring matters, alkaloids, etc., are proximate prin- 

 ciples of plants, while carbon, oxygen, and hydrogen in cer- 

 tain ratios are the ultimate elements of starch, sugar, and 

 other proximate principles. 



The methods in use for separating proximate principles 

 of vegetables and animals vary with nearly every sub- 

 stance examined; no scientific scheme has been yet de- 

 vised, nor can be until our knowledge of this branch of or- 

 ganic chemistry is vastly increased. 



On the other hand, ultimate organic analysis has been 

 brought to great perfection. The principles on which the 

 process is based are as follows : Organic bodies may be 

 considered as mainly made up of carbon, hydrogen, and 

 oxygen ; now when such a body is completely burned, or 

 oxidized (which is the same thing), the carbon, as you know, 

 burns to form carbonic anhydride, the hydrogen burns to 

 form water, and the oxygen escapes as such, or assists in 

 the oxidation. By taking a weighed amount, therefore, of 

 an organic substance, and oxidizing it carefully (by heating 

 with an oxidizing agent, or in a current of pure dry oxygen) 

 in a gas-tight apparatus, so arranged that all the carbonic 

 anhydride and water formed can be collected and weighed, 

 it is not difficult to calculate from the amounts of these 

 products the actual amount of carbon and of hydrogen in 

 the substance taken. How the operation is conducted, and 

 how the calculation is made, is a matter foreign to the 

 character of this work. 



