Oct. is. 1920 Germicidal Value of Some Chlorin Disinfectants 87 



The method of preparation as given by Dakin and Dunham is as 

 follows: To 1 liter of water add 12.5 gm. of bleaching powder and shake 

 vigorously. Add 12.5 gm. of powdered boric acid and shake again. 

 Allow the mixture to stand for some hours, preferably overnight, and 

 then filter. In actual practice the writer made the following modifica- 

 tions: The bleaching powder was rubbed up in a mortar with a little 

 water until the mixture had a creamy consistency. It was then trans- 

 ferred to a graduated flask or cylinder, the boric acid was added, and 

 then the amount of water necessary to make up the volume. The mix- 

 ture was shaken and then usually allowed to stand about two hours 

 before it was filtered through paper. 



Chlorin was used in these experiments in the form of an aqueous solu- 

 tion, standardized by titration with potassium iodid and sodium thiosul- 

 phate. 



Dilutions of these various disinfectants were made up for test as fol- 

 lows: Chloramin T dilutions were made by weighing the solid and dis- 

 solving it in the required amount of water. In certain experiments a 

 stock solution was made and titrated with potassium iodid and sodium 

 thiosulphate", and dilutions of the stock solution were then made so as 

 to contain specified amounts of "available chlorin." 1 But for the most 

 part dilutions were made up to contain a given weight of the solid 

 chloramin T. 



Dakin's solution and eusol were prepared according to the directions 

 previously given and were then titrated with potassium iodid and sodium 

 thiosulphate. Dilutions were then made from these original solutions 

 so as to contain a given amount of "sodium hypochlorite" or "hypo- 

 chlorous acid" for Dakin's solution and eusol, respectively. In certain 

 experiments the dilutions were made in both instances so as to contain 

 given amounts of "available chlorin." 



It has already been noted that according to Dakin and Dunham (5) 

 eusol contains calcium hypochlorite with an indefinite amount of free 

 hypochlorous acid. In a similar way Dakin's solution may contain not 

 only sodium hypochlorite but also more or less hypochlorous acid, as 

 stated by Cullen and Austin (3). As regards "available chlorin" 

 Rosenau (11) states that this really represents available oxygen rather 

 than available chlorin. All three terms, however, are convenient as 

 conventional symbols and will be so used in this paper. 



It should be stated further that for the purposes of certain experi- 

 ments it was necessary to modify the methods of preparing Dakin's 

 solution and eusol materially so as to secure more concentrated solutions. 

 In all such instances the changes made are indicated in connection with 

 the experiments. 



1 The quotation marks used in this and the following paragraph are intended to indicate that the terms 

 are used in a conventional way for purposes of comparison, and not in their literal sense. 



