i84 SEWAGE AND ITS PURIFICATION 



and was proved to be cheaper than sand filtration (3 feet thick 

 and at the rate of J gallon per square foot), combined with 

 the application of copper sulphate, which was suggested as an 

 alternative method for dealing with the problem. 



Electrolytic Processes. 



About 1859 Charles Watt first introduced electrolysed solu- 

 tions of the chlorides of alkalies or alkaline earths as bleaching 

 liquids. They contained chlorides and hypochlorites, but 

 apparently were more active than a solution prepared by pass- 

 ing chlorine into an alkali. Magnesium chloride was said to be 

 preferable. 



The Webster process allowed ordinary sewage to flow through 

 channels between iron electrodes, so that the chlorides were 

 electrolysed, the chlorine and oxygen liberated at the positive 

 pole deodorizing the sewage, while the iron salts formed assisted 

 in the purification. Later aluminium plates were substituted 

 for iron, and the aluminium hydrate generated acted as the 

 precipitant. A fault in practice was that a great part of the 

 sewage passed between the plates nearly or quite unaltered. 



Hermite electrolysed sea water, and either added it to sewage 

 or used the liquid for flushing latrines and sewers. Piton's 

 report on the trials at Nice illustrates a point now well estab- 

 lished, that an attempt to disinfect hinders or prevents the 

 natural bacteria from breaking down organic debris, in his 

 remark that " the Hermite solution, diluted to a strength of 

 about 0*25 gramme of chlorine per litre, does sterilize the faecal 

 matter in the sewers, but that, in spite of the rapid absorption' 

 of chlorine, the disintegration of paper and fsecal matter is no" 

 more rapid than when ordinary water is employed." The 

 system was tried at Worthing in 1894, and later at Ipswich, 

 and was fully examined by many authorities.^ 



The Lancet Commission (1894) found that in Hermite's 

 electrolysis of sea water the sodium chloride was not decom- 

 posed, only acting as a conductor ; but that the magnesium 

 chloride was converted into hypochlorite, which then deposited 

 magnesic hydrate, and left free hypochlorous acid in solution — 

 Mg(C10)2 + 2H2O = Mg(0H)2 + 2HCIO. 



The Hermite fluid agreed in properties with a solution of hypo- 

 chlorous acid, made by passing carbonic acid through a bleach- 



^ For further details of chlorine disinfection, see Rideal's " Disinfection and 

 Disinfectants," 1903, pp. 77-98. 



