1885.] The Removal of Micro- Organisms from Water. 



380 



to Mr. Verini, of the Colne Valley Waterworks, as well as to 

 Mr. Duncan and Mr. Newlands, for their kindness in permitting me 

 to carry out these experiments. 



At the Colne Valley Waterworks, the hard water obtained from a 

 deep well in the chalk is mixed with the requisite proportion of clear 

 lime-water, and then allowed to settle in open tanks. The subsidence 

 is so rapid that under favourable circumstances the upper layers of 

 water are, after three hours' time, fit for distribution. On the occa- 

 sion of my visit, however, boring operations were being carried on, 

 and the water was in consequence milky, and the necessary subsi- 

 dence after softening had to be increased to two days. I was 

 unfortunately unable to obtain a perfectly representative sample of 

 the water before softening, and the number of organisms found in the 

 untreated water is probably in excess of that which was actually 

 present in the unsoftened water itself. The following results were 

 obtained : — 



Unsoftened water 322 centres per c.c. 



Water after softening and 2 days' 

 subsidence (from main) 4 „ „ 



The almost complete absence of organisms in the softened water 

 shows how perfect a result is obtained even on the large scale. 



In the process of softening, due to Messrs. Gaillet and Huet as 

 practised at Mr. Duncan's, the water from an artesian well is mixed 

 with a suitable proportion of lime-water and caustic soda, the mixture 

 being then made to pass upwards through a tower provided with 

 diaphragms, which accelerate the precipitation of the carbonate of 

 lime. The passage through this tower occupies a period of about two 

 hours. Samples of water before and after treatment were examined 

 with the following results : — 



Well water 182 centres per c.c. 



(38 caused liquefaction of gelatine.) 

 „ after softening 4 centres per c.c. 



(None of the centres caused liquefac- 

 tion of gelatine.) 



These experiments, as well as those made in the laboratory, show- 

 that the softening of water by Clark's process is attended with a 

 great reduction in the number of organisms, the best results being 

 obtained when the clear liquid is separated from the precipitated 

 carbonate of lime as speedily as possible. 



Pasteur s Filter. — Through the kindness of Colonel Sir Francis 

 Bolton, R.E., I have had the opportunity of examining one of the 

 above filters, in which the water is made to pass through a cylinder 

 of biscuit-porcelain. The one with which my experiments were made 



2 f 2 



