178 SEWAGE AND ITS PURIFICATION 



(b) with the permanganate i in 5,000. The liquid running off 

 was collected and bacterially examined. The rapid destruction 

 of the permanganate was again noted. 



The permanganated sample was almost free from odour, and 

 on keeping for three days smelt much less foul than the other. 

 The cultivation experiments showed the following results : 



Colonies per c.c. 



Gelatine plates at 22° C (a) 1,930,000 



„ „ ,, (h) 85,000 



Agar plates at 37*5° C. ... ... (a) o*ooi c.c. gave numerous 



colonies, and plate was 

 too clouded in twenty 

 hours for counting. 

 ,, ,, „ ... ... {b) o'oi c.c. gave a similar 



result. 

 Carbolized gelatine plates at 22° C. (a) i22,-2oo 



(b) 4,830 



Although the permanganate has exercised considerable in- 

 fluence, destroying about 96 per cent, of the bacteria, the result 

 cannot be considered sterilization, and it will be noticed that 

 its effect upon those growing at blood heat and on carbolized 

 gelatine, which include those of the *' coli " group, was similar 

 to that on those growing on the ordinary gelatine plate. I 

 did not specially test in these experiments as to the survival 

 of spores of B. enteritidis sporogenes, but from previous work 

 with this organism I believe it to be extremely resistant 

 to permanganate. (See also p. 186, use of chlorine for this 

 purpose.) 



An important point in this treatment is that lower oxides of 

 manganese are always left in the sludge. Any metal having 

 two oxides which easily pass one into the other may act as a 

 carrier of oxygen from the air to organic matter, as is the case 

 with iron. Manganese has a still higher range of activity, 

 hence its oxygen compounds have long been used as destructors 

 of organic matter. The native mineral pyrolusite, Mn02, has 

 been used in the granular state in filters, or added in very fine 

 powder to sewage ; but beyond mechanical action it gives no 

 oxygen, and remains practically unchanged. A better result 

 occurs when it is mixed with carbonaceous matters and heated 

 in closed retorts, so as to reduce it to a lower state of oxidation. 

 On exposure to air and water a film of flocculent hydrated 

 peroxide is formed, which readily parts with oxygen to organic 

 matter in solution, reabsorbing oxygen from the air when the 



