92 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



Estimation of Acetone. 



1. Acetone is most usually estimated by converting it into iodoform with 

 -excess of iodine and caustic soda and titrating the excess of iodine with thio- 

 sulphate (Messinger's method). 



In the case of wood spirit *5 c.c. are added to 25 c.c. 'of N sodium 

 hydroxide contained in a stoppered bottle of 200 c.c. capacity ; the mixture 

 is well shaken and allowed to stand 5-10 minutes. 'aN iodine solution is 

 slowly run in from a burette drop by drop, shaking thoroughly till the upper 

 portion of the solution on standing for a minute becomes quite clear. A few 

 more c.c. of the iodine solution are run in so as to have an excess of about 

 25 per cent, and the solution is allowed to stand 10-15 minutes. 25 c.c. of 

 N sulphuric acid are added and the iodine which is liberated is titrated with 

 iN sodium thiosulphate solution, using starch as indicator. 



i c.c. *iN iodine solution = '00967 gm. acetone. 



A blank experiment should be made as sodium hydroxide may contain 

 nitrite. 



Aldehydes and other compounds which react with iodine are included in 

 this estimation, if present. 



2. Jolles has suggested the estimation of acetone by conversion into ace- 

 tone sodium bisulphite with excess of sodium hydrogen sulphite and titration 

 of the excess of sulphite with standard iodine solution. 



3-4 times the excess of the bisulphite solution of known strength is 

 added to the acetone solution ; after standing for 30 hours the excess is 

 titrated with *iN iodine solution. 



i mol. of NaHSO 3 = 2 atoms of I = i mol. of acetone. 



3. Deniges makes use of an insoluble compound of acetone with mercuric 

 sulphate for the estimation of acetone. The reagent is prepared by dissolving 

 5 gm. of mercuric oxide in 100 c.c. of water to which 20 c.c. of sulphuric 

 acid have been added. 



The acetone content of the solution must be not greater than '2 per cent. 

 so that strong solutions must be diluted. 25 c.c. of the reagent are added to 

 25 c.c. of the solution and the mixture heated on the water-bath for 10 

 minutes. The precipitate is filtered off on a weighed filter, washed with not 

 more than 100 c.c. of cold water, dried at 100 and weighed. The amount 

 of acetone in the precipitate, 3Hg 5 S 2 O 11 . 4C 3 H G O, is obtained by multiplying 

 by the factor -0609. 



This reaction can be carried out volumetrically by estimating the excess 

 or mercury. The mercuric sulphate solution must therefore be of known 

 strength. The filtrate and washings from the precipitate are collected and 

 made up to 100 c.c. To 20 c.c. of this solution 15 c.c. of ammonia, 50 c.c. 

 of water and 10 c.c. potassium cyanide solution (13 gm. per litre) are added. 

 The excess of cyanide is estimated by titration with *iN silver nitrate solution, 

 using potassium iodide as indicator, until there is a slight permanent precipitate. 



Since acetone is a decomposition product of aceto-acetic acid and 

 the two compounds are usually associated in tissues and extracts 

 of organs, the estimation of acetone in urine, etc., is combined with the 

 .estimation of aceto-acetic acid (p. 593). 



