THE RIVER WAN DLL. 29 



chalk, which, being insoluble, falls as minute crystals to the bottom ; 

 and the chalk dissolved falling also with this newly-formed chalk, the 

 water is freed from this material. This process is followed upon a 

 large scale at Caterham and other waterworks, whereby hard water 

 is converted into soft : this is thought by some people to be of great 

 advantage in a town supply, but I cannot myself fully acknowledge 

 the value of this chemical process, preferring for many purposes the 

 water as it flows naturally from the earth. 



In all chalk waters some saltpetre or other nitrates are invariably 

 found. Some eminent chemists consider this compound as a 

 proof of previous sewage contamination, others consider that the 

 nitrates arise from nitrogen derived from the atmosphere, but all 

 medical men agree that the nitrates are unimportant in a sanitary 

 point of view. 



Three great chemists, Professor Hoffman, Professor Miller, and Pro- 

 fessor Graham, recommended that London should seek its water-supply 

 from the chalk. I also have laboured in the same direction, and am 

 chairman of the South Essex Water-works, promoted for that object ; 

 but great and trustworthy men, as Professor Frankland and Mr. Bateman, 

 have continually opposed this view. However, during the past year 

 a change has come over the opinions of many of its opponents. Dr. 

 Frankland points out that the best water now supplied to London 

 comes directly from the chalk, and Professor Tyndall has demonstra- 

 tively proved, by the electric lamp, that chalk water contains no solid 

 particles. This philosopher has shown that solid particles reflect 

 light, and become visible, when a ray of light passes through the 

 water, and that all other water contains an immeasurably greater 

 number of particles than chalk water flowing from the bowels of 

 the earth. 



Professor Odling has kindly made me a careful analysis of the water 

 of the River Wandle : first, as it flowed through my garden ; secondly, 

 as it flowed through the Central Brook, which is within 200 yards of 

 its source ; and thirdly, at the Crystal Waterfall, near the spring at 

 Wallington House, of which the following is the result. He also 



