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XXIII. On the spontaneous purification of Thames water. 
M.J). F.R.S. ike. 
By John Bostock, 
Read April 30, 1829. 
In the Report respecting the analysis of the water of the Thames, which I pre- 
sented, 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 expe- 
riments 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 immedi- 
ately 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 clark-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 con- 
tinued for about eight weeks, when the water became perfectly transparent, 
without any unpleasant odour, although still retaining somewhat of its original 
dingy colour. 
After the formation of the scum mentioned above, the next change that I 
observed was its separation into large masses or flakes ; to these, as well as to 
the scum itself, a number of minute air bubbles were attached, to which, no 
