88 
THE MIDDLE LIAS OF NORTHAMPTONSHIRE. 
magnesia still more. Sulphates are very largely increased. 
It is the permanent hardness therefore that is chiefly 
increased. It is scarcely necessary for me to point out that 
some waters may be highly charged with mineral matter 
derived from the rocks through which they pass, without any 
contamination, so the general character of a water-bearing 
bed must be known before attributing excessive hardness in 
the water derived from it to contamination. 
Organic Contamination is a much more serious matter 
than inorganic, and animal matter more dangerous than 
vegetable, hence any analysis should be chiefly directed to 
the detection of the former. Animal and vegetable substances 
contain practically the same things, as a consequence of 
animals living on vegetables or other animals, but the pro¬ 
portions of these constituents vary. Animal matter contains 
more nitrogen relatively to the carbon than vegetable ; also 
the excrement of human beings is characterised by the pre¬ 
sence of more chlorine, in consequence of the great use of salt 
as a condiment. A determination of the relative amounts of 
organic carbon and nitrogen may be very valuable in a 
recently contaminated water, but since decomposition of the 
organic matter converts the carbon into carbonic acid gas, 
and this can no longer be specifically identified from that 
otherwise introduced, whereas the nitrogen still remains, the 
method does not seem of general application. 
Sewage matter is, unfortunately, very often discharged into, 
or allowed access to water which must be used by human 
beings. This matter is not only itself injurious, but it may at 
any time contain those living germs which are both the product 
and cause of diseases of an epidemic character. The most 
objectionable part of sewage in water is that held in mechanical 
suspension, and not that held in solution, for when the organic 
matter is fully decomposed the products, though soluble in 
the water, are not themselves injurious, because incapable of 
further change, at least of an objectionable kind, in the 
human body. 
Micro-organisms .—With the suspended matters we must 
class the living organic germs, for it is impossible to conceive 
that they could suffer solution, and consequent diffusion in the 
water, and at the same time retain their vitality. A chemical 
analysis fails to detect the presence of these organisms, and 
unless they are abundant a microscopic examination may 
also ; hence it is important to know whether they retain 
their vitality long, also whether they can be separated 
from the water. With regard to the first point, it is perhaps 
