ON PURE WATER. 
563 
all tlie oxygen is exhausted and the organic matters enter 
into a state of change in which dangerous compounds are 
generated. What the nature of these compounds is, neither 
the chemist nor the pathologist has been able to demon- 
strate. It is, however, well known that water under these 
circumstances becomes tainted ; that it gives off sulphuretted 
hydrogen and other stinking gases; and that, when taken 
internally, it produces sickness, diarrhoea, and other symp- 
toms of disease. It does not follow that these conditions wil] 
occur at all times. In cold weather water holds more oxygen 
in solution than in hot weather, and it frequently happens 
that it is only at certain seasons that water holding organic 
matters in solution becomes injurious. Heat not only robs 
water of its oxygen, but favours the rapid decomposition of 
animal and vegetable matters, so that it is most frequently 
during the warm season of the year thatwater becomes injurious. 
How to detect dead organic matter thus becomes a matter 
of great importance. Now, it has been found that this 
matter exists in water in two forms — suspended and dissolved. 
The suspended organic matter can be detected with the 
microscope. It is generally heavier than the water and 
settles at the bottom, although sometimes it floats on the 
surface. In either case it may be detected by the microscope, 
and is found to consist of minute, shapeless particles of animal 
and vegetable bodies. When these are in any appreciable 
quantities, the water is impure. 
When the organic matters are in a dissolved state, the 
microscope can no longer detect them. Chemical agents 
must be employed for their discovery. The method adopted 
by analytical chemists is to weigh the total solids of the water 
left by evaporation, and then to incinerate the portion left, and 
to weigh again. The matter lost by incineration is then regarded 
as organic matter. There is, however, another method, which, 
although less accurate, is easily applied, and requires no chemi- 
cal knowledge to use and appreciate. This process consists in 
adding a quantity of permanganate of potash or soda to the sus- 
pected water. All the permanganates have the power of giving’ 
a beautiful purple colour to water. A small quantity of organic 
matter will, however, decompose the permanganate and pre- 
vent its colour from being developed, or annihilate it if it 
has been once established. The best method of procedure in 
this case is to employ a solution of permanganate of potash of 
a known strength. I employ a solution of five grains to the 
ounce of distilled water. Half a pint or a pint of the water 
to be examined may be then taken, and five drops of the 
solution of permanganate added. According to the colour 
left in the water will be the amount of organic matter it con- 
