30 
On Water Supplies suited to 
concludes by describing the various means employed for purifi- 
cation. I would strongly recommend everyone who desires in- 
formation respecting water supplv to read Dr. Voelcker's paper, 
and note well the valuable instruction which it contains. 
I will here mention a very simple and rapid method of 
detecting organic impurity in water. Take two tumblers, fill 
one with water which is known to be pure — for example, 
distilled water, which can always be got at a chemist's — and 
the other with the water to be tried. Add to each 3 or 4 drops 
of a weak solution of permanganate of potash (two grains of the 
solid salt dissolved in a tumbler of distilled water) ; then the 
pure water will assume a clear pale magenta colour, but in the 
other, if contaminated, the colour will rapidly turn to a salmon 
hue, become much paler, and, if too much permanganate has not 
been added, the colour will almost entirely disappear. The 
use of the glass of distilled water is to enable a comparison of 
colours to be made. 
A friend of mine, a planter in Jamaica, was in the habit of 
daily testing, in the manner described, the water of the stream 
which flowed past his house, and from which he derived his 
supplv. On one occasion the colour turned to brick red ; he 
immediately searched the upper reaches of the stream, and at a 
distance of about a mile found the decomposing carcase of a 
cow lying in the water. 
The permanganate test is not infallible, because the colour of 
the solution is affected by some mineral substances ; but it is a 
useful guide in most cases. 
Since Dr. Voelcker's paper was written, the labours of Pasteur, 
Tyndall, Dr. Burdon Sanderson, and others, have greatly extended 
our knowledge of the true cause of the spread of contagious 
diseases. It is now known that the so-called zymotic diseases 
are propagated by living organisms, which increase and multiplv 
in impure waters — that is, waters charged with animal and 
vegetable matter ; and such waters are dangerous, not from the 
dead matter contained in solution, but on account of the proba- 
bility of dangerous living germs and organisms getting into 
them, developing and propagating with astonishing rapidfty. 
Absolutely pure water would contain no food tor living 
creatures : hence, the purer water is chemically, the safer it 
is likely to be. This great question of the propagation of con- 
tagious diseases among human beings and animals is still in 
the experimental stage, and much remains to be done before 
mankind will be in complete possession of the laws, which 
govern the spread of disease, and of the most efficient means of 
defence ; so that, although there can be no question that abso- 
lutely pure water is the best and most wholesome, there is as 
