Preparation of Dakin's Hypochlorite Solution. 41 



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A note on the preparation of Dakin's hypochlorite solution. 

 By Glenn E. Cullen and James H. Austin. 



[From the War Demonstration Hospital of the Rockefeller Institute.] 



In the preparation of Dakin's hypochlorite solution it has been 

 customary to adjust the reaction by the use of solid phenolphtha- 

 lein. In the preparation from sodium carbonate and bleaching 

 powder Dakin 1 added boric acid to the strongly alkaline hypo- 

 chlorite solution until it no longer colored solid phenolphthalein. 

 Daufresne 2 modified this technique by using a mixture of sodium 

 carbonate and sodium bicarbonate for decomposing the bleach and 

 also used solid phenolphthalein as the test for the reaction of the 

 solution. 



Investigations in this laboratory indicate that the reaction at 

 which solid phenolphthalein turns red with a hypochlorite solu- 

 tion is at a hydrogen ion concentration of about 1 X io -10 (pH 

 = 10), i. e., an alkalinity in terms of hydroxy 1 ions about 1,000 

 times that of water. Alkaline phenolphthalein solutions show a 

 flash color in hypochlorite solutions at a hydrogen ion concentra- 

 tion of about 1 X io -8 (pH = 8) or in the same unit an alkalinity 

 10 times that of water or one one-hundredth that of the turning 

 point of solid phenolphthalein in hypochlorite solution. Hypo- 

 chlorite solutions at a reaction corresponding to the color change 

 of phenolphthalein solution, i. e., pH = 8, are not stable. It is 

 desirable therefore to find the minimum alkalinity at which a 

 hypochlorite solution can maintain its concentration for a con- 

 venient period. We have found that this point is at a hydrogen 

 ion concentration of about io -8 ' 5 (pH = 8.5). At this reaction a 

 solution will maintain its hypochlorite content within the desired 

 range for about two days. Hypochlorite solutions prepared by 

 the use of phenolphthalein may vary as much as one hundred 

 times in alkalinity, depending upon the bleach and conditions. 

 This explains the variations in irritation that different observers 

 have reported. 



1 Dakin, H. D., British Med. Journal, August 28, 1915. 



2 Daufresne, M., Presse med., 24, 474, 1916. 



