152 PROCEEDINGS OF THE COTTESWOLD CLUB 



subsidence to take place, the sand and marl, and kaolin in 

 subsiding carry down much of the other impuritv. In 

 the experiments I have made with the Tewkesbury water 

 I find that allowing the turbid water to stand for a week 

 entirely clears it and reduces its organic impurity by just 

 one half, generally rendering it sufficiently pure to use 

 without further treatment. 



Comparisons with the Thames 



The Severn water is on the whole superior to that of 

 the Thames, and the Severn water above Tewkesbury 

 compares favourably with that of the Thames above 

 Oxford. I had a sample from the Thames one mile 

 above Oxford last year and compared it with a sample 

 taken from the Severn above Tewkesbury under similar 

 conditions of weather, there having been no rain for 

 several weeks. The result in the organic constituents 

 I give — 



Thames Severn 



Free Ammonia '05 '05 



Albuminoid Ammonia "14 09 



Oxygen consumed in 4 hours 84 i'i5 

 In parts per million. 



Of course Thames water is much harder than that of the 

 Severn, being derived from the Oolitic limestone, the 

 hardness being the one disadvantage of London water. 

 The filtered water of the Tewkesbury supply has just 

 about the same degree of organic puritv as the water 

 supphed by the more careful of the London Companies 

 to their consumers, but the raw Severn water at Tewkes- 

 bury averaging a much higher degree of purity than the 

 Thames at Hampton Court it is easier to arrive at as good 

 a result. The population of the polluting towns on the 

 Severn and its tributaries is less than of those on the 

 Thames and its tributaries, whilst the flow of water in 



