BACTERIA, DESTRUCTIVE INFLUENCES 41 B 



average figure of 20 per cent., the proportion of the three 

 substances used in the preparation of the solution must be 

 reduced or augmented. This is readily found by multi- 

 plying each of the three sets of figures, 184, 192, and 76, by 

 the factor ^ in which N represents the actual chlorine per 

 cent, in the chloride of lime. 



The following table drawn up by Daufresne is intended 

 to avoid this calculation and to give directly, according to 

 the amount of active chlorine contained in the chloride of 

 lime, the amounts needed to obtain a correct solution. 



Quantities to be Used to Obtain 10 Litres of Solution of 



Hypochlorite of 0.475 Per Cent. 

 Titration of Chloride 

 of Lime (Cl per cent.) 

 (English degrees). 



20 

 21 

 22 

 23 

 24 

 25 

 26 

 27 

 28 

 29 

 30 

 31 

 32 

 33 

 34 

 35 

 36 

 37 



It is well to titrate the finished product to measure the 

 content of hypochlorite of soda. This is done as follows : 



Measure off 10 c.c. of the solution, add 20 c.c. of 10 per 

 cent, solution of iodide of potassium, 2 c.c. of acetic acid, 

 then drop by drop a decinormal solution of hyposulphite 

 up to decolorization. The number of cubic centimeters 

 used multiplied by 0.03725 will give the weight of hypo- 

 chlorite of soda contained in 100 c.c. of solution. 



