1G2 W. M. DOHERTY. 



residue of vanillin there may be left is added to the alco- 

 holic distillate at first obtained. The residue from the 

 chloroform, which contains practically the whole of the 

 vanillin after drying in a vacuum over Oa01 2 is weighed in 

 a tared dish. If properly carried out the resultant vanillin 

 is generally pure enough, though at times it may contain 

 some impurity, and may even contain a foreign aldehydic 

 body such as heliotropin. The melting point should be 

 taken and a known portion dissolved in alcohol and com- 

 pared colorimetrically with a standard solution of pure 

 vanillin, using the reaction occasioned by bromine water 

 and ferrous sulphate. This colorimetric comparison which 

 I am about to describe may be used in determining the 

 amount of vanillin in the jalcoholic distillate before men- 

 tioned. Vanillin, I may state, can be accurately titrated 

 in alcoholic solution, phenol phthalein being the indicator, 

 one cubic centimetre of decinormal solution being equal to 

 0*0152 gramme of vanillin. 



When vanillin is treated in a dilute solution with bromine 

 water and ferrous sulphate (ammonium-ferrous sulphate 

 may also be used), a green colour is produced which is 

 proportional in its density to the quantity present. This 

 fact is the basis of an American official method which employs 

 a cream of lead hydroxide to decolorise the essence. I have 

 never been able to obtain uniform results with this method 

 as described, and have long since rejected the use of the 

 lead compound, retaining, however, the bromine and the 

 iron salt. I carry out the method as follows: — 



One cubic centimetre of the sample is treated in a small 

 separator with ten cubic centimetres, and then with five 

 cubic centimetres of ether, which on separation is allowed 

 to evaporate in a warm place on about thirty cubic centi- 

 metres of distilled water. When all the ether has evapor- 

 ated, the watery solution is filtered through a moistened 



