38 
POPULAR SCIENCE REVIEW. 
The presence of much nitrogenous organic matter or free 
ammonia in water is held by all chemists to be a proof of con- 
tamination. Dr. Frankland regards the presence of nitrates in 
the same light. But Dr. Odling, Professor Wanklyn, and 
others, look upon nitrates as giving no certain information on 
the matter. It is true that they may be formed by the oxida- 
tion of ammonia, this having previously been formed by the 
fermentation of organic matter ; but nitrates exist in deep well- 
water, to which it is hard to believe that sewage or its deriva- 
tives gain access ; and they must also be formed in the soil, 
from the albuminoid parts of plants. On the other hand, living 
vegetable matter in water abstracts nitrates, and thus the 
amount of them may be no sufficient measure of its previous 
pollution. 
Organic matters in water are hurtful because of the putre- 
faction and fermentation which they undergo. But when these 
changes have reached their final stage, and the organic nitrogen 
has been wholly converted into nitrates or nitrites, the water is 
not necessarily unwholesome from its mere chemical contents. 
The danger is that germs of disease — of typhoid fever and 
cholera, or the ova of intestinal worms — may remain unchanged, 
suspended, but not dissolved, in the water. This is especially 
to be feared in the case of shallow wells, and of streams into 
which sewage is poured. That typhoid fever and cholera 
are in this way propagated by drinking water has been proved 
repeatedly. 
The extent to which sewage is oxidised and rendered harm- 
less during its transport by rivers is a question of supreme 
importance ; unfortunately it is also one on which authorities 
differ. Dr. Letheby believes that if ordinary sewage, such as 
that of London, “ be mixed with twenty times its bulk of the 
ordinary river water and flows a dozen miles or so, there is not 
a particle of that sewage to be discovered by any chemical pro- 
cess.” Other chemists incline to the same opinion, or at least 
believe that in most cases sewage is destroyed if carried in this 
way for long distances.* Dr. Frankland and Mr. Morton devote 
much attention to this question ; and as the result of many 
analyses of several river waters, including that of the Thames, 
they believe that 66 there is no river in the United Kingdom 
long enough to secure the oxidation and destruction of any 
sewage which may be discharged into it, even at its source.” 
Against these statements should be placed the admission of 
the Commissioners that the tributaries of the Thames are 
often more highly polluted than is the river itself at Hampton. 
* See the Minutes of Evidence of the Water Supply Commission. The 
main points hearing on this question are recapitulated in the Commissioners’ 
Report, pp. lxxv-lxxxvii. 
