THE RIVER WANDLE. 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 chemists consider this compound as a proof of pre- 

 vious 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 riiany 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. He 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 



' My son has recently found that the air contains as much nitrogen in combi- 

 nation as is found in nitrates in chalk water. 



