STERILIZATION i8i 



with ordinary water containing carbonic acid, the latter decom- 

 poses the hypochlorite, setting free hypochlorous acid — 



Ca(C10)2 + CO2 + H2O = CaCOg + 2HCIO. 



Hypochlorous acid can either combine with organic matter 

 directly, forming innocuous compounds, or can furnish hydro- 

 hloric acid and nascent oxygen. 

 " Chloros " is a solution of sodium hypochlorite NaClO, 

 containing 10 per cent, of available chlorine. It has recently 

 been used by the Metropolitan Water Board for sterilizing the 

 effluents from the Hertford Sewage Works, as the outfall is 

 not far from the intake of the Lea water-supply to London. 

 Allusion has already been made to the use of chloride of lime 

 at Birmingham (p. 155) in small quantity along with slaked 

 ■■■lime ; as the latter absorbs the carbonic acid, the action of the 

 IBhypochlorite is extremely slow. Chloride of lime was used 

 IBbefore 1884, and again in 1887, for the river Thames during 

 l^the hot weather, but it was shown that " unless large and 

 f "* continuous doses were kept up," the foulness of the stream 

 was not controlled. Hofmann and Frankland found in 1859 

 that it required 400 pounds of chloride of lime to deodorize a 

 million gallons of London sewage, the effluent remaining in- 

 offensive for three days. On the river Brent in 1896, when 

 complaints were made of the effluvium, chloride of lime was 

 scattered on each bank during the warm weather. Its use in 

 dustbins, gulleys, streets, and urinals is well known. Louis 

 Parkes,^ speaking of the insanitary condition of wood pave- 

 ments during dry weather where horse-droppings are frequent, 

 recommends that " wood-paved streets should be watered from 

 carts containing a weak antiseptic and deodorant solution, 

 which will inhibit the growth of the putrefactive microbes on 

 the wood surface. Probably the best would be a weak chlorine 

 solution, say i part of chlorine in 10,000 to 20,000 parts of 

 water . . . being volatile, it leaves no residue on the road." 

 But free chlorine, even in this dilution, would attack the iron 

 fittings of the carts and the grids of the sewers, and be itself 

 removed as basic ferric chloride. A I per cent, solution of 



oxygen yielded as it does in solutions of the free element. In the manufactured 

 products lime or soda is always present in excess for the sake of stability ; but 

 all of them deteriorate when stored, especially in presence of light. The available 

 chlorine requires to be frequently controlled by analyses. In " chloride of lime " 

 it is expected to be 33 to 34 per cent. ; in " chloros " solution it is regulated to 

 10 per cent, 

 ^ British Medical journal, December 9, 189;;. 



