STAGNANT WATER. 243 
That of the river Thames, impregnated as it would 
appear to be with putrid remains, is soft and good, 
when taken up at low water; and, after rest and filtra- 
tion, is found to contain but a small portion of any thing 
either noxious or unpleasant. It is preferred, by mari- 
ners, to most other water for sea store; but it soon be- 
comes putrid, and undergoes a remarkable spontaneous 
change. When, after having been kept a month or 
two, a cask is opened, a quantity of inflammable air 
escapes, and the water is black and nauseous. If, in this 
state, it be racked off into large earthen vessels (oil jars 
it is said are commonly used for the purpose), and ex- 
posed to the air, it gradually deposits a portion of black 
slimy mud, and becomes perfectly clear, sweet, and fit 
for use. 
278. STAGNANT WATER contains greater impurities 
than any other. In ponds and marshes particularly, it is filled 
with the remains of animal and vegetable matters, which are 
there undergoing a gradual decomposition. 
The water of lakes is not, in general, so much contaminated 
as this; but from the same cause, it frequently has a slimy ap~ 
pearance, a brownish colour, and an unpleasant taste. 
From the putrefying contents of stagnant water, nu- 
triment is afforded to various living plants and insects 
which there supply the place of those that perish. Its 
taste is vapid, unpleasant, and wholly destitute of that 
agreeable freshness which is found in spring water. It 
is, however, generally soft, and, by filtration, it maybe 
freed from many of its impurities. 
The air which issues frojii marshes and stagnant 
pools is extremely noxious, and is the cause of agues 
and other distressing complaints, to such persons as 
reside in the neighbourhood of them or are much ex- 
posed to them; and the injurious effects of such air 
have also been considered to extend to the internal use 
of these waters. 
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