DR. BOSTOCK ON THE PURIFICATION OF THAMES WATER. 
289 
contained, And acquired a state of apparent purity, which might render it suf- 
ficiently proper for many purposes, yet that the quantity of saline matter is 
increased as much as four-fold. The greatest proportionate increase is in the 
muriates, which are very nearly twelve times more in the purified water than in 
the Thames water in its ordinary state. The carbonate of lime is between two 
and three times as abundant as before, and the sulphate of lime between five 
and six times. I may remark, that this water, when examined in its foul state, 
gave very obvious indications of both sulphur and ammonia, neither of which 
could be detected after depuration. 
This depurating process may be denominated a species of fermentation ; i. e. 
an operation, where a substance, without any addition, undergoes a change in 
the arrangement of its component parts, and a new compound or compounds are 
produced. The newly formed compounds were, in this case, entirely gaseous, 
and, except a part of the carbonic acid, were discharged. The saline bodies, 
being not affected by this process, remained in solution, leaving the fluid free 
indeed from what are considered as impurities, yet so much loaded with earthy 
and neutral salts, as to be converted from a soft into a hard water*. The source 
of the saline bodies may be supposed to be the organic substances, principally of 
an animal origin, which are so copiously deposited in the Thames ; of these the 
most abundant are the excrementitious matters, as well as the parts of various 
undecomposed animal bodies. The different species of the softer and more 
soluble animal compounds act as the ferment, and are themselves destroyed, 
while the salts which were attached to them are left behind. It may be con- 
ceived therefore, that the more foul is the water, the more complete will be the 
subsequent process of depuration ; and we have hence an explanation of the 
popular opinion, that the Thames water is peculiarly valuable for sea stores, its 
extreme impurity inducing the fermentative process, and thus removing from 
it all those substances which can cause it to undergo any further alteration. 
The brown colour which the water exhibited after its depuration appeared 
to depend on the solution of a minute quantity of what is generally termed 
extractive matter, and which is observed in water that contains decayed vege- 
* The terms hard and soft, as applied to water, are obviously relative ; but water which contains 
as much as 5 grains in the pint of saline matter, is generally regarded as too hard for many oecono- 
mical and manufacturing processes. The water in question contained 4.36 grains per pint. 
2 p 
MDCCCXXIX. 
