26 MEDICAL BACTERIOLOGY 



the commercial Javelle water, Labarraque's solution and all the solutions pre- 

 pared by any other procedure than the following: 



(b) "Concentration. The concentration of sodium hypochlorite must be 

 exactly between 0.45 and 0.50 per cent. Below 0.45 per cent, of hypochlorite 

 the solution is not sufficiently active; above 0.50 per cent, it becomes irritating. 



"Chemicals Required for the Preparation. Three chemical substances are 

 indispensable to Dakin's solution: Chlorinated lime, anhydrous sodium carbon- 

 ate and sodium bicarbonate. Among these three products, the latter two are 

 of a practically adequate constancy, but this is not the case with the first. Its 

 content in active chlorine (decoloring chlorine) varies within wide limits, and it 

 is absolutely indispensable to titrate it before using it. 



"Titration of the Chlorinated Lime. There must be on hand for this special 

 purpose. : 



A 25-cc. buret graduated in o.i cc. 



i pipette gaged for 10 cc. 



A decinormal solution of sodium thiosulphate (hyposulphite). This 

 decinormal solution of sodium thiosulphate can be obtained in the market; it 

 can also be prepared by dissolving 25 Gm. of pure crystalline sodium thiosul- 

 phate in i liter of distilled water, and verifying by the decoloration of an equal 

 volume of the decinormal solution of iodine by this solution. The iodine is 

 prepared by dissolving 1.27 Gm. iodine and 5 Gm. potassium iodide in ioo\'cc. of 

 water. 



"The material for the dosage thus provided, a sample of the provision of 

 chlorinated lime on hand is taken up either with a special sound or in small 

 quantities from the mass, which then are carefully mixed. 



" Weigh out 20 Gm. of this average sample, mix it as completely as possible 

 with i liter of ordinary water, and leave it in contact for a few hours, agitating 

 it from time to time. Filter. 



"Measure exactly with the gaged pipette 10 cc. of the clear fluid; add to 

 it 20 cc. of a i : 10 solution of potassium iodide and 2 cc. of acetic or hydrochloric 

 acid. Drop, a drop at a time, into this mixture a decinormal solution of sodium 

 thiosulphate until decoloration is complete. 



" The number of cubic centimeters of the hypochlorite solution required for 

 complete decoloration, multiplied by 1.775, gives the weight of the active chlorine 

 contained in 100 Gm. of the chlorinated lime. 



"This figure being known, it is applied to the accompanying table, which will 

 give the quantities of chlorinated lime, of sodium carbonate and of sodium 

 bicarbonate which are to be employed to prepare 10 liters of Dakin's solution. 



"Preparation of Dakin's Solution. To prepare 10 liters of the solution: 



1. "Weigh exactly the quantities of chlorinated lime, sodium carbonate and 

 sodium bicarbonate which have been determined in the course of the preceding 

 trial. 



2. "Place in a 1 2-liter jar the chlorinated lime and 5 liters of ordinary water, 

 agitate vigorously for a few minutes, and leave in contact for from 6 to 12 

 hours, over night, for instance. 



