240 CONSIDERATION OF CARBON COMPOUNDS. 



analysis by which the elements in organic substances are deter- 

 mined is generally called ultimate or elementary analysis. 



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

 teristic tests that these substances may be recognized by them ; 

 these reactions will be mentioned in their 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 may be identified by 

 passing the gas through lime-water), the organic nature of this 

 substance is established. 



The presence of hydrogen can be proven by allowing the 

 gaseous products of the combustion to pass through a cool 

 glass tube, when drops of water will be deposited. 



It is somewhat difficult to show by qualitative analysis the 

 presence or absence of oxygen in an organic compound, and its 

 determination is therefore generally omitted. 



The presence of nitrogen is determined by heating the sub- 

 stance with dry soda-lime (a mixture of two parts of calcium 

 hydrate and one part of sodium hydrate), when the nitrogen is 

 converted into ammonia gas, which may be recognized by its 

 odor or by its action on paper moistened with solution of cupric 

 sulphate, a dark blue color indicating ammonia. 



Ultimate or elementary analysis. The quantitative determina- 

 tion of carbon and hydrogen is accomplished by the following 

 process : A weighed quantity of the pure and dry substance is 

 mixed with dry cupric oxide, and this mixture introduced into 

 a glass tube, the open end of which is connected by means 

 of a perforated cork and tubing with two glass vessels, one 

 of which (generally a U-shaped tube) is filled with pieces of 

 calcium chloride, the other (usually a tube provided with 

 several bulbs) with solution of potassium hydrate. The two 



