Sewage Precipitation. 55 



Notes on Sewage Precipitation. By Harry Grimshaw, 

 F.C.S. 



{Received December, iot/1, iSpi.) 



Among the innumerable chemical substances which 

 have been used for the precipitation of the impurities in 

 sewage, the salts of iron have of late years come prominently 

 to the front, and have been much studied and experimented 

 with in this relation. Both the natural and artificial iron 

 compounds have been used with considerable success in 

 different parts of the country. 



The authorities of Buxton have taken advantage of a 

 natural iron water, which they have conveyed a distance of 

 a mile and adopted as the precipitating medium for their 

 sewage, with the addition of a little lime. 



The success of the Buxton process is such, that the river 

 Wye below the sewage works contains, I believe, fish which 

 greatly exceed in size and number those in the same river 

 above the sewage outfall. 



The Metropolitan Board of Works, it is stated, found 

 very considerable benefit accrue from the addition of a few 

 grains per gallon of an iron salt to the London sewage. In 

 fact, experts are apparently coming to the conclusion that 

 the salts of iron, if they can be procured at a cheap enough 

 rate, are bound to be of great assistance in sewage puri- 

 fication. This is not only so in England, but is also being 

 discovered on the Continent, as indicated, for instance, by 

 the work done by some of the foreign chemists, as stated 

 in recent numbers of the Chemical Trade Journal. 



I do not propose, at present, to go into any exhaustive 

 analysis of the respective merits of the numerous and 

 various salts of iron which have been investigated in this 



