92 BIOLOGY AND TECHNIQUE 



almost twice that amount of chlorin has been introduced, frequent titrations 

 of the hypochlorite content must be commenced to determine the proper 

 point at which to stop the introduction of the chlorin. 



Titration of Dakin's Solution. To 10 c.c. of the Dakin solution, add 

 approximately 5 c.c. of a 10 per cent solution of potassium iodid and 3 c.c. 

 of glacial acetic acid. lodin is liberated and dissolves in the excess of iodid 



N 

 present. Dilute with water to about 50 c.c. A standard -- thiosulphate 



solution is then added from a burette until the solution is just rendered 

 colorless. The number of cubic centimeters required to effect this result 

 multiplied by the factor 0.0372 gives the percentage of sodium hypochlorite 

 present in the Dakin solution. 



N 

 Preparation of Standard Thiosulphate Solution. Dissolve exactly 



24.82 grams of pure crystalline sodium thiosulphate in water and make 

 up to exactly 1 liter. One c.c. of this standard solution is equivalent to 

 0.00372 gram of sodium hypochlorite. 



Titration of Bleaching Powder. Bleaching powders vary considerably in 

 their "available chlorin" content, so that it is desirable to determine the 

 available chlorine in each large batch. Bleaching powders with less than 

 20 per cent available chlorin should be rejected. Exceptional samples may 

 contain as high as 35 per cent available chlorine. 



The available chlorin content may be determined as follows: exactly 

 10 grams of bleaching powder made up of small samples from different 

 parts of the jar, in order to obtain a representative sample, are well shaken 

 with a liter of water. After standing about six hours the solution is filtered 

 and a 10 c.c. sample of the filtrate is titrated in exactly the same manner 

 as in the titration of Dakin's solution. In this case the number of cubic 

 centimeters of decinormal thiosulphate required to decolorize, multiplied by 

 the factor 3.55, gives the percentage of active chlorin in the bleaching 

 powder. 



The chlorin antiseptics in general, and particularly the hypo- 

 chlorite type, have the disadvantage of exerting their disinfectant 

 action over an exceedingly short space of time. The reaction be- 

 tween the hypochlorite solution and the proteins of the bacterial body 

 or of the serum and pus in the wound, is almost instantaneous, and 

 having taken place, no further toxic action is shown. It is, there- 

 fore, necessary in treating wounds with these solutions, to repeat 

 the application at frequent intervals, or else to apply through some 

 sort of a continuous feed apparatus so that a fresh supply of the 

 antiseptic is brought in contact with the wound at short intervals. 



In order to overcome this disadvantage to some extent, DaHn 



