﻿2 RAMSDEN, Two New Aldehyde Reactions. 



by starting with sodium metabisulphite (thus carrying 

 out a suggestion of Mr. Thos. Tyrer made publicly some 

 time ago). Atest solution is made as follows : 50 grammes 

 of sodium metabisulphite are dissolved in 100 ccs. of water 

 and filtered. To this strongly acid solution 50 % NaOH 

 is added until nearly neutral. 2 ccs. of the solution are 

 now taken, made up to 50 ccs. with distilled water and 

 1 cc. of phenolpthalein solution added, and the whole put 

 into a Nessler glass. Decinormal Na 2 C0 3 or NaOH is 

 added until the phenolphthalein indicates a very slight 

 alkalinity. The original solution is then neutralised with 

 the requisite amountof Na 2 CO ;3 or NaOH, and then allowed 

 to stand for two days in a stoppered bottle. 2 ccs. of this 

 solution added to 48 ccs. of distilled water and 1 cc. of 

 phenolphthalein should only give the faintest possible 

 pink colouration. 



To test for formaldehyde 50 ccs. of the solution 

 (neutral) supposed to contain formaldehyde are taken in a 

 Nessler glass, and 2 ccs. of the reagent and 1 cc. phenol- 

 phthalein added. A pink to red colour is produced if 

 formaldehyde is present. A control with distilled water 

 should always be made. 



The delicacy of the test with formaldehyde is about 

 4 parts per million. 



As might be expected, other aldehydes, e.g. acetalde- 

 hyde, give the reaction, but not with the same dilution as 

 formaldehyde. 



It is important that care should be taken to use 

 aldehyde — free alcohol in the preparation of the phenol- 

 phthalein solution, as some samples contain aldehyde in 

 appreciable quantity. The reaction may be expressed by 

 the equation 



Na 2 S0 3 + HCHO + H a O = (NaHSO s HCHO) + NaOH. 

 Coloured or turbid solutions must first be distilled. 



