XXIII. On the spontaneous purification of Thames water

Abstract

In the Report respecting the analysis of the water of the Thames, which I presented, in April 1828, to the Commissioners appointed by His Majesty to inquire into the supply of water in the Metropolis, I have stated that when the expe­riments were nearly brought to a close, a quantity of water was sent to me, purporting to have been “taken in the river, in the current of, and immedi­ately at the mouth of the King’s Scholars’ Pond sewer.” I described it as “in a state of extreme impurity, opaque with filth, and exhaling a highly foetid odour.” When it had been about a week in my possession, a considerable quantity of black water subsided from it, but the fluid was still dark-coloured and opaque, and nearly as offensive as at first, while the odour and colour were only in part removed by being passed through a layer of sand and charcoal, six inches in thickness. The water remained for some time in my laboratory without being attended to; when after an interval of some weeks, I observed that a great change had taken place in its appearance. It was become much clearer, whilst nearly the whole of the sediment had risen to the surface, where it formed a pretty regular stratum of about half an inch in thickness; the odour, however, still continued extremely offensive, perhaps even more so than at first. From this time the process of depuration, which had thus spontaneously commenced, was con­tinued for about eight weeks, when the water became perfectly transparent, without any unpleasant odour, although still retaining somewhat of its original dingy colour.