242 AIDS TO BACTERIOLOGY 



sterilise water in thirty minutes, but the use of an acid 

 compound is to be deprecated. In the British Army 

 tabloids of sodium bisulphate, flavoured with lemon and 

 saccharin, are supplied for the use of cavalry. In 

 practice it is found that men soon get tired of the taste 

 of water treated in this way, and, though the tabloids 

 may be issued, they are not regularly used. 



Potassium permanganate is effective, but it is best 

 followed by treatment with alum. Copper sulphate in 

 a very weak solution kills algae (p. 254), and its use has 

 been suggested for the routine disinfection of water. 



Iodine has been employed and is quite effective, but 

 the water must be subsequently treated with sufficient 

 hyposulphite of soda to neutralise the iodine. 



Of late years sterilisation of water by chlorine has come 

 into use, and its employment is rapidly increasing. Its 

 use was suggested by Major Nessfield in about the year 

 1897, who showed that colon and typhoid bacilli could 

 be killed by the addition of chlorine to water in high 

 dilutions. Later it was found that the addition of small 

 quantities of a dilute solution of bleaching powder was 

 equally effective. The less a water contains of organic 

 matter and chemical compounds that combine with 

 bleaching powder, the less is needed for sterilisation. 



The essential point is to add as much bleaching powder 

 as is required to kill the disease-producing organism 

 (which is assumed to have occurred if no living coli- 

 group organisms can be recovered after treatment), but 

 to avoid excess, because even a very small excess of 

 bleaching powder gives a most unpleasant taste to water. 

 This taste is brought out more strongly when water is 

 made into tea. Some individuals are very sensitive to 

 small quantities of bleaching powder. Moor and Hewlett, 

 in a report to the L.G.B. (Report of the Medical Officer 

 to the Local Government Board, 1909-10), examined 

 the processes available for the purification of chalk waters, 

 and reported in favour of sterilisation by bleaching 

 powder. In those investigations it was shown that 

 0'25 part of chlorine (equivalent to approximately 0-75 

 part of good bleaching powder) per million killed colon 

 bacilli in chalk water in thirty minutes. The amount of 

 chlorine necessary varies. Sims Woodhead found the 

 amount of chlorine necessary to kill the whole of the 



