176 SEWAGE AND ITS PURIFICATION 



four hours, but i in i,ooo was fatal under that time. B.enteri- 

 tidis was very similar. With B. dy sentence and M. melitensis 

 fifteen hours was effective. 



K ferrous sulphate solution was also tried in comparison. One 

 in 100,000 was ineffective ; i in 10,000 was fatal to B. typhosus 

 under seven hours, and to B. enteritidis under forty-eight hours; 

 I in 1,000 killed B. coli in less than twenty-four hours. He 

 therefore finds ferrous sulphate almost as effective as copper 

 sulphate, but it has the disadvantage of rendering the water 

 yellow and turbid. 



He confirmed the germicidal power of bright copper surfaces. 

 B. typhosus in a copper vessel was still living at twelve hours, but 

 was dead at twenty-four. With ordinary tap-water organisms, 

 the number being 1,020 per c.c. at first, only 8 per c.c. were 

 left after twenty-four hours ; the main decrease occurred in the 

 first hour, and the liquefying bacteria decreased from sixteen to 

 two in three hours, and to none in twenty hours. No copper 

 was found in solution'. 



He concluded that clean iron was nearly equal to copper, 

 and zinc had almost the same effect ; but as the metals must 

 be bright, iron soon loses its value by rusting, and zinc also 

 becomes oxidized. Strips of ordinary zinc foil up to forty-eight 

 hours had not sterilized any of the organisms. Iron coated 

 with zinc, or galvanized iron, should give good results. 



An attempt to sterilize urine containing pathogenic organisms, 

 by keeping it in a copper vessel, was not successful after twenty- 

 four hours' contact, and it was considered that this was due to 

 the action of the urine on the metal. 



Lead, tin, and a control glass vessel showed practically no 

 effect. The conclusions of the paper are that in tanks for the 

 storage of water, iron, copper, and zinc as galvanized iron 

 show only a slight difference in bactericidal power, and that 

 *' zinc, or iron, coated with zinc, though less rapid in action 

 than copper, yet after twenty-four to forty-eight hours appears 

 to free the water from typhoid organisms." 



It is possible to thoroughly deodorize sewage by permanganate 

 and sulphuric acid (giving ozonized oxygen), either before or after 

 the removal of the suspended matters by precipitation.^ Sodium 

 manganate, as a cheaper salt, was used for the London sewage 

 from 1884 to 1887 by introducing it into sewers at different 



1 See Report of Commission of 1882, on the effects of the discharge of the 

 sewage of London into the Thames, vol. xi., p. 142. 



