192 SEWAGE AND ITS PURIFICATION 



this way the amount of salt required to yield a given amount 

 of available chlorine is considerably reduced. 



The higher oxides of chlorine have been employed for dis- 

 infection and destruction of organic matter, but expense has 

 militated against their use on a large scale for sewage. The 

 Berge process prepares peroxide of chlorine thus : 



3KCIO3 + 2H2SO4 = KCIO4 + 2KHSO4 + CI2O4. 



The gas is passed into water, and this solution allowed to mix 

 with the polluted effluent. Organic matter is quickly oxidized 

 by the gas, so that the liquid shows after treatment less organic 

 matter and an increase in the chlorides formed by the reaction 

 of the oxide on the carbonates in solution. The quantity 

 required to produce sterility in drinking-waters or effluents prac- 

 tically free from organic matter, by contact for at least fifteen 

 minutes, is given at i gramme of potassium chlorate per cubic 

 metre of water. B. colt and typhosus in Seine water were killed 

 in three hours' contact by 0*24 part of CI2O4 per 100,000, and 

 even when the amount does not exceed o*o8 (or say i part per 

 million) considerable reduction in the number of bacteria is 

 assured. The solution used contains 0*013 per cent, of per- 

 oxide, and is added to the effluent or water to be purified 

 in the proportion of about i per cent. 



In Germany Wiederhold used chlorate and hydrochloric acid 

 during the cholera epidemic. The expense, offensive odours, 

 and danger of explosion, caused their discontinuance. 



Sterilization by Acids. — The large majority of bacteria, 

 especially the pathogenic forms, have a preference for neutral 

 or slightly alkaline solutions, and it has long been known that 

 in culture liquids they refuse to grow, and die, even with small 

 amounts of acid. Koch first noticed the fact with regard to 

 the cholera organism, Kitasato showed that it was killed by 

 dilute sulphuric or hydrochloric acid in a few hours, and 

 A. Stutzer found that 0*05 per cent, of sulphuric acid was fatal 

 in fifteen minutes, 0*02 per cent, in twenty-four hours. Ivanoff, 

 with 0*04 to o*o8 per cent, sulphuric acid, destroyed cholera 

 organisms in Berlin and Potsdam sewage. In the Liernur 

 process, and in that of Beck and Henkel's of 1901, sewage is 

 sterilized by sulphuric acid. The successful use of acids in 

 disinfection is very old, and was limited by inconveniences, 

 which, however, would not affect their employment for liquids 

 in the very dilute state shown above to be effective. Stronger 



