STERILIZATION 177 



points ; being strongly alkaline, it disengaged ammonia, which 

 was neutralized by acid treatment at the outfall. 



The amount of oxygen liberated from manganates and per- 

 manganates depends upon the way they are applied. The 

 maximum, when permanganate with sulphuric acid acts on 

 organic matter, is 5 atoms, thus : 



K^MnPs + 3H2SO4 = K2SO, + 2MnS04+ 3H2O + 5O. 



If the acid be insufficient, a brown precipitate of hydrated 

 peroxide falls, and only 3 atoms of oxygen are liberated : 



K2Mn208 + H2SO4 + 3H2O = K2SO4 + 2Mn(OH)4 + 3O. 



Manganate spontaneously gives up i atom of oxygen with great 

 readiness : 



Na2Mn04+ 3H2O = 2NaOH + Mn(0H)4 + O. 



With a dilute acid, even carbonic, in excess, it yields per- 

 manganate and hydrated peroxide : 



3Na2Mn04 + 2H2SO4 = Na2Mn208 4- Mn(OH)4 + 2NaS04 ; 



the permanganate further changing as shown above. 



Processes for recovery of the manganese or iron oxides from 

 the pressed sludge have not been commercially successful. 



Manganates and permanganates are rapidly destroyed by 

 harmless organic matter and other substances, so that there is 

 often no remainder left for bactericidal action. They were 

 formerly much used in street watering-carts, and an experiment 

 of my own may be illustrative.^ 



The Westminster Vestry had for some time used permanganate 

 in their water-carts in the proportion of 2 ounces to 400 gallons, 

 or I in 32,000, the 400 gallons covering about 600 square yards 

 on a dry and 3,000 square yards on a wet day. The reasons 

 given for discontinuing it are interesting : (i) That it was com- 

 plained of as damaging the asphalt ; (2) that it was more costly 

 than other disinfectants ; (3) that being without odour the rate- 

 payers had no belief that a place had been disinfected ; (4) that 

 it attacked the iron tanks and fittings ; (5) that children collected 

 the pink liquid in various utensils, and sometimes drank it. 



To test the bacterial efficiency of a i in 5,000 solution, at the 

 rate per yard mentioned above, I watered two plots of asphalt 

 roadway in Victoria Street, under ordinary day conditions of 

 horse droppings, etc., (a) with ordinary water, and the other 

 ^ Sanitary Record, July 27, 1900. 



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