56 Mr, Harry Grimshaw on 



connection, but merely to call attention to some experi- 

 ments of my own with a special preparation of a per-salt of 

 iron, which is, I understand, coming into use, and which 

 would appear to be destined to take a high place as a 

 sewage precipitant. It is a solution of the perchloride and 

 peroxide of iron prepared in the following manner : — A 

 peroxide of iron, either anhydrous or hydrated, but in 

 either case free from ferrous compounds, is dissolved to 

 saturation in hydrochloric acid, and to this solution 

 hydrated ferric oxide is then added, which dissolves largely 

 in the ferric chloride, forming a basic chloride or oxy- 

 chloride of iron. This compound appears to have very 

 great power of precipitation on the impurities of sewage, 

 which is possibly due to its great neutrality and to the easy 

 dissociation of the basic compound. The excess of oxide 

 of iron, also, no doubt, " weights " the precipitated matters, 

 and helps to cause a quick subsidence. 



The three points I wish to illustrate by my experiments 

 are (i) the remarkably quick action of the salt in causing 

 coagulation and precipitation of the sewage ; (2) to show 

 that the conditions of acidity, alkalinity, or neutrality affect 

 the action of sewage precipitants very materially ; (3) that 

 by a proper method of treatment some manufacturing 

 effluents are also precipitated directly by this iron salt, 

 whilst those which are not precipitated alone are very 

 completely clarified when mixed with a sufficient quantity 

 of sewage. 



(1) The first sample is of the sewage of Failsworth, which 

 is an example of one nearly free from manufacturing 

 refuse, but containing domestic and farm drainage. You 

 will see that one drop of the iron salt completely clarifies 

 this sewage, and on subsidence gives a liquid some degrees 

 clearer and brighter than Manchester water when unfiltered. 



The mixed sewage of Salford and Pendleton contains 

 a large proportion of manufacturing refuse, and, in fact, 



