560 Prof. Woodhead, The results of 



Another suggestion was that sterilisation by ultra-violet rays 

 might be adopted, especially as the Cambridge water, beautifully 

 clear, would allow of the ready passage of these rays through its 

 substance. On making enquiries, however, we could then hear of 

 only one small apparatus, an apparatus capable of sterilising some 

 132 gallons only per hour of an ordinary water supply, more or 

 less according to the translucency of the water. The apparatus a 

 Cooper-Hewitt lamp made from transparent quartz requires for 

 its proper working 3 amperes of current at 110 volts. With this 

 the process of sterilisation had been carried on on a purely experi- 

 mental scale and the apparatus required would be somewhat costly 

 as it had been determined by the Water Company that any 

 sterilisation experiments carried out on their behalf must be on 

 a sufficiently large scale to supply sterilised water in sufficient 

 quantities for, say, a couple of thousand people. 



Ozonisation of the water, the next method that was suggested, 

 has passed somewhat beyond the experimental stage, but although 

 ozonising installations for the sterilisation of water could be seen 

 in various towns in France and Germanj^ there were none to which 

 we could gain access in this country. On making enquiries it was 

 found that the water supplied to Paris is very like the Cambridge 

 water in its chemical composition. We were told that it had 

 been selected specially because of its high degree of hardness, the 

 Commission appointed to find a water supply for Paris main- 

 taining that the use of a hard water is attended with fewer 

 dangers to the human subject than when a soft water is used. 

 The Commission evidently had in view, in this connection, rickets, 

 imperfect bone formation and lead poisoning. At the request of 

 the Water Company Mr Heycock and I journeyed to Paris where 

 we found that the pure chalk water becomes somewhat muddied 

 and otherwise contaminated on its passage from its source by the 

 Marne river to the intake of the Paris Water Company at St Maur 

 where it contains a very large number of the Bacillus coli com- 

 munis. In order to get rid of a large proportion of these organisms 

 and to remove the organic matter, the presence of both of which 

 would interfere greatly with the process of sterilisation by ozone, 

 the water at St Maur is passed through sand-filters, by means of 

 which process a certain degree of clarity — almost equal to that 

 of the Cambridge water — the removal of a considerable quantity 

 of organic matter and the reduction of the number of the Bacillus 

 coli to such a point that, usually, not more than one Bacillus coli 

 to 40 c.c. of water is obtained. As a matter of actual experience, 

 however, at the time we visited St Maur, these filtei's were not 

 working quite up to this standard, for although the whole of the 

 organic matter, except some of that in solution and the whole of 

 the inorganic matter in suspension was removed the water then 



