ON THE AIR AND WATER OF TOWNS. 29 
change is retarded, and this is the best way for small quantities. It would 
‘be the best way for large quantities also if it were perfectly pure, as then no 
hange whatever could occur. 
_ But even when water is to be kept a day only there is an objection to 
sterns in most cases. If there be a little impurity deposited, the daily 
increase soon makes it a great impurity ; ‘and although the fact of the im- 
purity remaining in the cistern be a sufficient proof that it has not been 
c nk or otherwise used, yet such a reservoir of impurity is constantly apt 
o be giving off some offensive matter. If the impurities be of the kind 
‘common in Thames water, and in the water of many of the companies, or in 
‘the Manchester water, or that of some other towns, they are of a kind 
capable of producing animals very disgusting, and large enough to be seen 
"sometimes by the naked eye. If even nothing but a green matter is per- 
_ ceptible, this is unpleasing in itself, besides never being alone, but inhabited 
_ by numerous little creatures visible with a microscope, although not so dis- 
_ gusting as those to be met with in the flocculent precipitate of the Thames 
water. Underground cisterns in London, when supplied with very pure 
‘water, contain in them some of the most disagreeable of these living forms ; 
and although apparently a good method of keeping water cool, it is a plan 
to which the impossibility of cleaning is a great objection. Even stone cis- 
terns, however clean stone in itself may be, are often filthy receptacles of 
_ water, for which not the stone but the water is to blame. If wood be used 
_ pure water can never be obtained; and the enormous amount of crenic acid 
_ formed, with the peculiar smell of rotten wood, which happens even in new 
barrels, form great objections. The reddish flocculent matter is also not 
without inhabitants, for which it affords a good shelter. 
_ If I come to the conclusion that water should either be kept in large 
quantities or kept constantly running, it may be said this was known to 
“every one; true, but when this happens, it is the business of science to ex- 
plain why it is so; and if this be not done, there are constantly found some 
who deny the general impression until a proof be obtained. 
_ Dr. Clark, who has done so much towards giving the country in general 
an interest in the purification of water, advises also the alkalinity of the 
water to be taken at the same time as the hardness. I have found it more 
convenient to take the fixed contents in a gallon of water. By comparing 
‘this with the hardness, we find the excess of impurities not affecting the 
hardness. To do this and take the alkalinity also, would probably be the 
best mode of treatment. In the springs at the source of the Thames the 
fixed matter and the hardness are equal, or nearly so, whilst in the Thames at 
London, the fixed matter rises as high as twenty-six grains per gallon, whilst 
the hardness is fifteen degrees. This gradual increase of salts not affecting 
the hardness is a good indication of the rate of impurity in the progress of 
the river, and is a great cause of making it a less agreeable draught. 
From experiments which I have made on the cause of vapidness in water, 
Tam led to believe that the salts of alkalies are some of the most common 
mts. Dr. Clark has shown the great influence of temperature on the 
taste of water, but it seemed to me not enough to explain the frequency of 
the occurrence of tasteless water. 
_ Water with carbonic acid in it did not taste vapid when raised slowly to 
100° Fahr., the acidity being sufficient to prevent it, as I believe. 
_ Lambeth water boiled and cooled could not be made to taste as well as 
ater which had not the same amount of salts in it. 
Pangbourne water, although excellent, when boiled down so as to saturate 
