40 
POPULAR SCIENCE REVIEW. 
Classified according to softness, the waters stand thus : — 
1. Rain water 
2. Upland surface water 
3. Surface water from cultivated 
land 
4. Polluted river water 
5. Spring water 
6. Deep-well water 
7. Shallow-well water 
As regards the water supply of London, the Report just pub- 
lished will greatly strengthen the case of those who are discon- 
tented with our present supply — not only as to its quality, modes 
of distribution and control, but also as to its source. It is not 
pleasant to think of drinking water mixed with sewage, even 
although the sewage may enter the river miles away, and the 
water be most efficiently filtered before delivery. To many 
who read this Report, what may now be only a matter of taste 
will become a matter of conviction. The Commissioners 
unhesitatingly condemn the water supplied from the Thames 
and the Lea ; that supplied by the Kent Waterworks Company 
to London, from deep wells in the chalk, is good water, its only 
fault being a high degree of hardness. The New River Com- 
pany partly derives its supply from springs and wells in the 
chalk. According to this Report the amount thus obtained is 
relatively too small to affect the general quality of the water ; 
hut absolutely the supply so obtained is considerable, nearly, 
12,000,000 gallons per day. 
Chalk water is always hard, chiefly from the presence of 
bicarbonate of lime. Dr. Clark invented a process by which 
this 66 temporary hardness ” may be removed, which consists in 
mixing water saturated with lime with the water to be soft- 
ened. The excess of carbonic acid, which holds the carbonate 
of lime in solution in the hard water, is then transferred to the 
free lime, and the whole falls down as insoluble carbonate of 
lime. Apart from the advantage of softening the water, this 
process has other recommendations ; much organic matter is 
carried down with the precipitate, and the water will keep 
better in reservoirs than when in the natural state. 
This process has been applied by Mr. Homersham to several 
waterworks. The water from the deep well at Plumstead was 
thus softened until the year 1861, when the works were bought 
by the Kent Company. None of the water now supplied to 
London is treated in this manner ; but the process is used at 
Aylesbury, Canterbury, Caterham, and Tring, with the following 
results : — 
Hardness (parts per 100,000) 
Before 
After 
softening. 
softening. 
Canterbury . 
. 26-3 
49 
Caterham 
. 21-2 
4*4 
Tring . 
. 26-3 
3*2 
