5^ Mr. Harry Grimshaw on 



The effluent from the ordinary lime process of sewage 

 treatment, also passable in general appearance, would no 

 doubt show a similar presence of coaguable nitrogenous 

 matter if subjected to the action of the iron salt, but I have 

 not had an opportunity to try this. 



The proportion of the iron salt required for the Salford 

 sewage is from 15 to 20 grains as a rule, but sometimes not 

 more than 12 grains to the gallon. I am informed that the 

 cost of this quantity amounts to one to two pounds 

 sterling per million gallons. 



(2) The next series of experiments illustrates the pecu- 

 liarities of condition which are necessary for the successful 

 purification of samples of sewage of different natures. 



The sewage last-named would require, in its natural 

 state, a very large excess of the precipitant to clarify it, on 

 account of the unusually large quantity of free ammonia 

 contained. We must, therefore, add a small quantity of a 

 crude acid, say brown vitriol, or mix it with a faintly acid 

 sewage, which is often available ; after which, as shown, a 

 single drop of the iron salt clarifies it completely. On the 

 other hand, a sewage too acid, say with manufacturing 

 waste water, must be almost neutralised by the addition of 

 a little lime, in which case it is best to add the iron salt 

 previously, as is done at Buxton. 



Some descriptions of sewage, however, must be rendered 

 distinctly acid if treated alone, or no precipitation can be 

 effected. The sewage of Pendleton is sometimes of this 

 character, but, as a rule, becomes mixed with so much from 

 other parts of Salford that it creates no special difficulty. 



These few experiments are, I think, sufficient to show 

 that the chemist requires to know the exact condition of 

 the sewage under treatment, and to make an intelligent 

 allowance for it, or what is really a comparatively simple 

 problem becomes most inexplicably complicated. 



(3) A few experiments upon the effluent waters from a 



