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Analytical Notes. 



For purposes of the quantitative determination of aldehydes and 

 ketones, F. de Myttenaere 1 ) has endeavoured to make use of their property 

 of combining with hydrocyanic acid, forming cyanohydrines. He has, in 

 part, obtained practicable results. The estimation is carried out as follows: 

 the compound in question was diluted with hydrocyanic acid in an aqueous 

 or a faintly alkaline solution, in the proportion of about 1 molecule of 

 aldehyde or ketone to 4 molecules hydrocyanic acid. The dilution had 

 been arranged so that 100 cc. of the liquid should contain about 0,4 grams 

 hydrocyanic acid. The mixtures were first heated for 75 minutes on the 

 water-bath in a sealed flask and afterwards left standing for 12 hours 

 at room temperature. After this the total and the still remaining free 

 hydrocyanic acid were determined and the acid in combination with the 

 aldehyde or ketone was calculated from the difference; the proportion 

 represented by the compounds which had entered into reaction being 

 calculated in turn from the data thus obtained. 



De Myttenaere estimates the total hydrocyanic acid by the following 

 method: exactly 6 cc. of the solution to be tested is added to 75 cc. 

 water; 10 drops of 40 p. c. soda liquor, 10 cc. 17 p. c. ammonia solution, 

 and finally a few drops of a 10 p. c. solution of potassium iodide is added 

 and the mixture titrated with centinormal silver solution. To determine 

 the free hydrocyanic acid, the author adds to 50 cc. centinormal silver 

 solution, placed in a measuring flask of 100 cc. capacity, exactly 3 cc. of 

 the solution to be tested, shakes, adds water to 100 cc, filters, and estimates 

 in 50 cc. filtrate the excess of silver nitrate with centinormal ammonium 

 sulphocyanide, ferri-ammonium aluminate being used as an indicator. 



The author has obtained good results with the lower fatty aldehydes 

 as well as with benzaldehyde, but the method failed with citral, vanillin, 

 and dextrose, and also with ketones. 



On the estimation of citronellal in citronella oil see p. 40. 



According to A. Seidell 2 ), the estimation of thymol may be carried 

 out as follows: 0,1 to 0,5 grams thymol is placed in a flask of 300 cc. 

 capacity with 1 to 2 cc. carbon tetrachloride and 100 cc. water. Bromine 

 I vapour is then poured into the mixture so long as the brown colour 

 ^persists after shaking. After 30 minutes 5 cc. carbon disulphide, and 

 immediately afterwards an aqueous 20 p. c. potassium iodide solution in 

 excess are added to the liquid. The* liberated iodine is titrated with deci- 

 normal thiosulphate solution. After this, 2 p. c. aqueous potassium iodate 

 solution is added and the iodine set free is again titrated. The thio- 

 sulphate which is used up in the second titration corresponds to the 



1 ) Annal. de Pharm. 18 (1912), 1. 



2 ) Americ. chem. Journ. 47 (1912), 508. From a copy kindly sent to us. 



9* 



