COMPOSITION OF ORGANIC COMPOUNDS 29 



2. Nitrogen. 



(a) As Ammonia. A portion of the substance (e.g. caseinogen) is 

 ground up with soda-lime and heated in a dry test tube. Ammonia 

 is given off as shown by the smell, by litmus paper and by the 

 production of white fumes when a glass rod dipped in hydrochloric 

 acid is held over the mouth of the tube (Will and Varrentrapp's 

 method). 



The peculiar smell of burning flesh, horn, etc., produced on heat- 

 ing such substances alone, also indicates the presence of nitrogen. 



(f) As Sodium Cyanide. A small piece of metallic sodium is heated 

 in a small dry test tube of hard glass until the metal begins to boil ; 

 successive minute portions of the substance (dried egg albumin) are 

 added. The heating is continued for a short time, the tube is cooled, 

 and the lower end of it is broken in a. mortar, containing a few drops 

 of alcohol ; water is added when effervescence has ceased. The solu- 

 tion is transferred to a test tube, warmed and filtered. To the filtrate 

 some ferrous sulphate solution (this must be freshly prepared by dis- 

 solving a few small crystals in a little water) and caustic soda are 

 added and it is boiled for a few minutes. It is cooled and a drop or 

 two of ferric chloride and excess of dilute hydrochloric acid are added. 

 A precipitate or coloration of Prussian blue indicates the presence of 

 nitrogen (Lassaigne's method). 



Note. It is important that the substance be made to come into 

 proper contact with the sodium. 



Castellands Modification of this Test. A small quantity of the sub- 

 stance is intimately mixed with about ten times its quantity of equal 

 parts of magnesium powder and dry sodium carbonate and gently 

 heated until the magnesium burns ; it is then heated to redness as 

 with the sodium (). The remainder of process is carried out as 

 described above, i.e. breaking the tube in a mortar, etc. 



3. Halogens. 



(a) Beilsteiris Test. A piece of copper wire is heated in a Bunsen 

 flame until the flame is no longer coloured green. A little of the sub- 

 stance, e.g. chloroform, is placed on it and it is again heated. Copper 

 chloride is formed which colours the flame green. 



(ti) Halogen may also be detected by means of sodium employed 

 just as in the nitrogen test. The filtered solution is acidified with 

 nitric acid, boiled to remove any hydrocyanic acid which will be 

 formed if the substance also contains nitrogen, and then treated with 

 silver nitrate. 



