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19
given that ten tons of powdered chalk lime should
be at once introduced into the water and scattered
over its surface.*
On the 4th of June the Basin was emptied,
and remained empty for two days. It was found
that the depth of the mud did not exceed a few
inches in any part, except in the neighbourhood of
the bridge, so that the condition of the channel
was satisfactory, as compared with former years.
The improvement in the health of the surrounding
inhabitants, and particularly of the families of the
bargemen, consequently on the removal of the
water, was marked. During the few weeks which
immediately preceded the admission of fresh
* When fresh lime is added to water like that of the Canal
Basin in which a good deal of carbonate of lime in the soluble
state is dissolved, it enters into chemical combination with the
carbonate, so as to form insoluble carbonate of lime, or chalk.
This, as soon as it is formed, falls to the bottom, carrying with it
any impurities which happen to be suspended in the water; so
that by adding more lime to water already containing a certain
quantity, both that which is added and that which previously
existed are got rid of. The advantage to be gained by the process
does not however lie in the removal of the lime, but of the light
matters which it carries down with it; for this reason it is an
effectual method of disinfection, provided that the channel is clean
and the water remains tranquil; but if the bottom consists of
organic mud which is frequently agitated, the floating putrescible
matters are so abundant and so rapidly replaced after removal that
the effect of liming must be very inconsiderable.