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98
preferable to those of sodium and potassium or even calcium, because
for the purposes of rendering the three last mentioned solutions stable,
there would have to be used hydroxide of the metals of the alkali or the
alkaline earth calcium, which are extremely caustic, alkaline, and very
soluble, and where varying strengths of electrolytic fluid, containing the
hypochlorites of sodium and potassium, are produced, one may add too
much or too little of the hydroxides of the alkalies when working
with unskilled labour. But when the extremely insoluble hydroxide
or oxide of magnesium is added and mixed, one can add and stir in any
quantity, but only the necessary amount will be absorbed.
It is common knowledge that metallic hypochlorites of the alkali
metals and alkaline earths may be obtained in the pure state by
neutralising hypochlorous acid with certain metallic hydroxides of the
alkali metals and alkaline earth groups. But to obtain hypochlorite of
magnesium, even upon a small scale, to say nothing of the large quantity
manufactured in Poplar, by means of electricity, and to render it stable by
using the hydroxide or oxide of magnesium, should, in view of the
practical experience obtained in Poplar during the past six years,
necessitate no criticism.
Even supposing a solution of hypochlorite of calcium be produced
more cheaply from bleaching powder by lixiviation than a solution of
hypochlorite of magnesium by an electrolytic process—which is the better
fluid for municipal domestic purposes? I venture to think the latter is,
for the reason stated above, the public have consequently a better article.
Bleaching powder is subject to great fluctuations in price, and it
contains from 33 to 37 per cent, of available chlorine, but it very rapidly
loses its efficiency when exposed to the atmosphere, and it is no
exaggeration to say that a further 15 to 18 per cent, must be deducted
from the efficiency of available chlorine when bought to the chlorine as
ultimately obtained.
Another point is, that with chloride of lime two-thirds, residue, must
be disposed of in some way ; it is generally allowed to accumulate on
waste ground, where in time it becomes a nuisance. I certainly think
that if hypochlorite of lime were extracted from bleaching powder there
would be more labour required than with the electrolytic process adopted
in Poplar.
Respecting the cost of the plant, its depreciation and the maintenance
of the depot in which it is housed, it is certainly unfair at the present time
to criticise past figures because six years ago a plant was installed and