566 
POPULAR SCIENCE REVIEW. 
hoped that there will no longer be supineness or ignorance 
enough to prevent legislation on this very important subject. 
But even water from springs maybe contaminated. Springs 
are often situated in highly cultivated agricultural districts_, 
among populations utterly negligent of the distribution of the 
water-courses that flow through them^ and may thus reach the 
population which they supply with water^ highly charged with 
organic matters. It is only by proper filtration at the works, 
by which the water is supplied to towns, that danger can be 
obviated, either in the case of water supplied by rivers or 
springs. It is a consolation to know that through the care and 
intelligence exhibited by a large number of our water com- 
panies, water is now supplied to many of our large towns of an 
unexceptionable character. This is remarkably the case in 
London, where the water of the Thames, receiving the sewage 
of several large towns in its course, can nevertheless be supplied 
in a state of purity, which will bear comparisoru with most 
other large towns in England. It is necessary that a vigilant 
eye should be kept on the nature of this supply, and in London 
we are undoubtedly indebted to the monthly analysis of water 
supplied by the Thames companies, published by the Registrar- 
General, for the maintenance of the integrity of our water. 
There are, however, large numbers of the population who 
are not within the reach of our public supplies, and who are 
obliged to have recourse to pumps and wells, ponds, rivers, and 
ditches, for the water which they drink. Such persons cannot 
be too cautious in the employment of the water they are com- 
pelled to take. Wherever water is of a doubtful character, 
then filtration should be had recourse to. The filtration of 
water can be effected by passing it through sand, pebbles, 
sandstone, sponge, and charcoal. Of these agents, charcoal 
is most efficient. Filters made with charcoal are now 
manufactured on a large scale, and are, in most instances, 
efficient means of rendering impure water pure. Such 
filters should be employed when waters are of a doubtful 
character, and only filtered water should be used for drinking 
purposes.* 
Where, however, filtered water cannot be had, it should be 
known that one of the most effectual means of purifying water 
is submitting it to boiling. This does not get rid of all its 
inorganic constituents, but it effectually destroys organic 
matters. It is undoubtedly insipid (which may be obviated 
* There are two classes of filters sold for public use, one of which is con- 
structed of loose charcoal, and performs its duties admirably ; whilst 
another class is made of charcoal more or less compressed and moulded, 
which prevents the due purification of the water. 
