Treatment of Sewage with Basic Per- Salts of Iron. 145 



During these experiments the sewage was of what may 

 be called an average impurity, the Albumenoid Ammonia, 

 which is one of the chief indicators of this, being 0*63 parts 

 per 100,000 in the sewage settled in 12 hours, or, in other 

 words, the soluble albumenoid matter in the sewage yielded 

 063 parts of ammonia per 100,000, or &$ parts per million. 



The sewage of this character was treated with an 

 amount of the solution of Basic Persulphate of Iron of 

 100° Twaddle (or sp. gr. 1*5), varying from 15 to 20 grains 

 per gallon of sewage, or 20 to 25 cwt. per million gallons. 

 •In order to secure the best results with a sewage of this 

 nature, lime at the rate of 5 to 10 cwt. per million gallons 

 was also added. 



The average results of the one month's trial in these 

 experimental tanks, as shown in Table L, was an effluent 

 by precipitation only containing 0*29 parts per 100,000 

 of albumenoid ammonia, which was further reduced by 

 filtration to 0*15. 



The quantity of iron salt used, in the trial, was to be 

 restricted to one ton of the standard strength (ioo° Twaddle, 

 or 1*5 sp. gr.) to the million gallons of sewage. This was 

 about the quantity used in the smaller trials previously 

 alluded to, but it appeared very problematical whether, in 

 very much greater space and with the greatly increased 

 volume involved in dealing with the whole sewage, it would 

 be practicable to work to such a nice point in regard to 

 quantities. 



Further, the question presented itself, whether the greater 

 rate of flow, ten to one, in the main tanks, as compared to 

 that in the experimental tanks, would not require a greater 

 proportionate amount of precipitate to add weight to the 

 flocculent particles. 



However the attempt was made, in the first place, to 

 ascertain whether the proposed quantity of one ton per 

 million gallons, together with about 5 cwt. of lime, would 



