268 Dr. Bostock on the Purification of Tliames Water. 



Subdivision : Portland Stone. 

 Although this rock, as has been before stated, is observed in 

 points crowning the oolitic series in England and France, its 

 organic remains have not been well described except in Mid- 

 land and Southern England : I shall therefore content myself 

 by referring to Mr. Conybeare's lists.* 

 [To be continued.] 



XXXVII. On the spontaneous Purification of Thames Water. 



By John Bostock, M.D. F.R.S. S^c. f 

 TN the Report respecting the analysis of the water of the 

 -*- Thames, which I presented, in April 1828, to the Commis- 

 sioners appointed by His Majesty to inquire into the supply 

 of water in the metropolis, 1 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 immediately at the mouth of the King's 

 Scholars' Pond sewer." I described it as " in a state of ex- 

 treme impurity, opaque with filth, and exhaling a highly fcetid 

 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 offen- 

 sive 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 with- 

 out being attended to ; when, after an interval of some weeks, 

 I observed that a great change had taken place in its appear- 

 ance. 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 de- 

 puration, which had thus spontaneously commenced, was con- 

 tinued for about eight weeks, when the water became perfectly 

 transparent, without any unpleasant odour, although still re- 

 taining 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 mi- 

 nute air bubbles were attached, to which, no doubt, they owed 

 their buoyancy : after some time the masses again subsided, 

 leaving the fluid almost totally free from any visible extraneous 

 matter. The quantity of gas discharged was inconsiderable, 



• Outlines of the Geology of England and Wales, p. 176. 

 t From the Philosophical Transactions for 1829, part ii. 



so 



