TRANSACT [OXS OF SECTION B. 



709 



together corresponding with that of the water removed — and the stopper of tho 

 funnel is then inserted, care being taken that no air bubbles are enclosed. 



AVithin the separating funnel there is now a layer of ferrous sulphate below, 

 next the water, and above all the ammonia. These are mixed by inverting the 

 vessel once or twice by a swinging motion, when a greenish turbid mi.Kture result.'s, 

 which rapidly darkens as the dissolved oxygen is absorbed. After fifteen minutes 

 the vessel (still stoppered) is inverted, and its tube or lower extremity (now. Low- 

 ever, the upper one) is nearly tilled with a mixture of equal volumes of sulphuric 

 acid and water. The tap is then opened, when the acid flows downwards into 

 the alkaline mixture, and in the course of a few minutes dissolves the iron hydrates, 

 forming a clear solution. This is then run off into a porcelain dish, and there 

 titrated, either with permanganate or bichromate, conveniently of the strength 

 1 c.c. = 1 c.c. of dissolved oxygen at N.T.P. 



In the authors' experiment the separating funnel had a capacity of o32'o c.c, 

 practically ^ litre ; and its tube contained, when nearly full, about 8 c.c. of 

 diluted sulphuric acid. About 7 c.c. of the water was removed, 5 c.c. of standard 

 ferrous sulphate solution added and about 2 c.c. of strong ammonia. The ferrous 

 sulphate solution contained about 12 s-rams of the crystallised salt in 250 c.c. of 

 distilled water. It was standardised for each determination by titrating 5 c.c. in 

 a porcelain basin, mixed with the same volume of the water under examination as 

 employed in the dissolved oxygen determination and the same volume of acid. 



For all practical purposes the dissolved oxygen contained in the volume of 

 water which the separating funnel holds amounts to the dill'erence between tho 

 burette readings for the blank experiment and for the actual determination. The 

 following are a few typical results : — 



It will be seen that for sea water and sewage effluents bichromate gives more 

 accurate results than permanganate. 



4. The Utilisation of Setcage Sludge. By Professor W. B. Bottomley, 

 M.A., rii.D., King's College, London. 



No one sy.stem of sewage treatment is univer."-ally applicable. Local conditions 

 must determine which system is best for any locality. Parliamentary returns in 

 1894 gave 233 sanitary districts in England and AYales where systems for treating 

 sewage hy precipitation were in operation. In most cases the sludge was not only 

 valueless, but a nuisance. 



The author experimented with specially prepared sewage sludge, enriched by 

 the use of phosphatic material in treating the sewage. A crude phosphatic reck 

 was treated with sulphuric acid slightly in excess of the amount necessary to 

 combine with the cxides of iron and aluminium present ; the resultant substance 



