HALOGEN DERIVATIVES OF HYDROCARBONS 61 



A few drops of chloroform are heated with dilute caustic soda. 

 The presence of chloride is tested for in a small portion of the solu- 

 tion, the remainder is neutralised exactly, if it be still alkaline, and 

 heated with mercuric chloride solution. A deposit of mercurous 

 chloride and mercury shows the presence of formate. 



Tests for Impurities in Chloroform. 



A quantity of the specimen is shaken up with two volumes of water. 

 The water is separated and silver nitrate is added. Pure chloroform 

 gives no reaction, but a precipitate of silver chloride indicates the 

 presence of chlorides. If, on heating, the precipitate blackens the 

 presence of aldehyde or formic acid is indicated. The water should 

 not react with blue litmus. 



Chloroform is not soluble in concentrated sulphuric acid. Any 

 darkening which occurs on shaking them together is due to the 

 presence of aldehyde, methyl alcohol, etc. The presence of alcohol in 

 chloroform may be detected by shaking some of the specimen with 

 five volumes of water, filtering through a wet paper, and testing for 

 alcohol in the filtrate by the iodoform reaction (p. 67). 



Tests for Chloroform. 



(1) A red or yellow precipitate of cuprous oxide is formed on add- 

 ing some solution of chloroform in water to Fehling's solution (p. 84) 

 and heating. 



(2) Carbylamine Reaction. To the dilute solution of chloroform 

 in water is added some alcoholic sodium hydroxide and a drop of 

 aniline and the mixture heated. Phenyl isonitrile or carbylamine 

 is formed, which has a disgusting smell : 



CHC1 3 + 3 KOH + C 6 H 5 NH 2 = C 6 H 6 NC + aKCl + 3 H 2 O. 

 This reaction is extraordinarily sensitive and will detect one part 

 iof chloroform in 5000 parts of alcohol. It is also given by bromoform, 

 odoform, chloral, trichloracetic acid and substances which yield chloro- 

 form when treated with alkali. 



From liquids, such as blood, it is better to remove the chloroform 

 as described under estimation and to test the liquid in the receiver. 



Estimation of Chloroform. 



Hydrochloric acid is formed when chloroform vapour mixed with 

 hydrogen is passed through a red hot tube. 



Hydrogen is slowly passed into a flask containing the solution of chloroform 

 and the flask is gently heated. The mixed vapours are passed through a 

 short, heated combustion tube containing platinum wire gauze or loose 

 asbestos and into a receiver containing water. The contents of the receiver 

 are titrated with standard alkali or precipitated with silver nitrate. As 

 acetylene and hydrogen cyanide may also be present the contents ot 

 receiver should be boiled before titrating or precipitating. 



This procedure may be used for detecting and estimating chlorofc 

 blood and other liquids which do not contain other chlorinated compounds. 



