CHEMISTRY. 185 



of organic nitrogen. Chemical works contribute chiefly mineral 

 impurities, which often communicate to water extreme hardness, 

 and other disagreeable and even poisonous properties." 



The Commission made numerous analyses of the water of the 

 various streams in the district under examination, directing their 

 inquiries mainly to : (1) Total solid matters in solution ; (2) 

 organic carbon ; (3) organic nitrogen ; (4) ammonia (in the form 

 of carbonate of ammonium) ; (5) nitrogen, as nitrates and nitrites ; 

 (6) total combined nitrogen ; (7) chlorine ; (8) hardening con- 

 stituents ; (9) suspended matters. In regard to the alleged self- 

 purification of polluted streams they say : 



" It has often been stated, but, so far as we know, without any 

 proof, that the organic matter contained in sewage and other 

 similar polluting materials is rapidly oxidized during the flow of 

 a river into which such materials are discharged. Thus it has 

 been asserted that, if sewage be mixed with 20 times its volume 

 of river water, the organic matter which it contains will be 

 oxidized and completely disappear, while the river is flowing ' a 

 dozen miles or so." 1 (Report of Royal Commissioners of Water Sup- 

 ply, p. Ixxix.) We thought it very undesirable that a subject of 

 such vital importance to our inquiry should any longer rest on mere 

 opinion, and we therefore determined to submit it to careful ex- 

 perimental investigation. During our winter visit to the basins of 

 the Mersey and Ribble, a very favorable opportunity presented it- 

 self for the solution of this important problem. The river Mersey, 

 after receiving the drainage of many towns and manufactories 

 above the Stretford Road Bridge, flows thence 13 miles to its 

 junction with the Irwell without encountering any other mate- 

 rial source of impurity, although its volume is somewhat aug- 

 mented by unpolluted affluents. The river Irwell, after passing 

 Manchester, falls over a weir at Throstlenest and runs 11 miles 

 to its junction with the Mersey without further pollution. Lastly, 

 the river Darwen, which is greatly polluted by the sewage of 

 Over Darwen, Lower Darwen, and Blackburn, joins the Blake- 

 water just below the latter town, and then flows 13 miles to near 

 its junction with the Ribble without further pollution, although 

 its 'volume is more than doubled by various unpolluted afflu- 

 ents. 



*' We took samples of water at the top and bottom of the 

 courses of these various rivers at the places just indicated." 

 From the results of the analysis of these samples, and from other 

 experiments undertaken in order to decide this point (for which 

 the reader is referred to the original document, pp. 19 and 20), 

 it is evident that, " so far from sewage mixed with 20 times its 

 volume of water being 'oxidized during a flow of 10 or 12 miles, 

 scarcely two-thirds of it would be so destroyed in a flow of 168 

 miles at the rate of 1 mile per hour. Whether we examine the 

 organic pollution at different points of its flow, or the rate of the 

 disappearance of the organic matter of sewage, when the latter 

 is mixed with fresh water and violently agitated in contact with 

 air, or, finally, the rate at which dissolved oxygen disappears in 

 16* 



