Longer the period juices are in contact with carbonic acid,
greater will be the effect produced.
Ferric sulphate has been very little used for refuse water
purification, owing to cost of its manufacture. If roasted pyrites, a
waste product of certain chemical factories, are sprinkled with
sulphuric acid of 66 deg. B., and thoroughly mixed for several hours, at a
temperature of 100 deg. to 156 deg. F., the pyrites will soon be covered with
a white substance which is ferric sulphate. Precipitates from ferric
sulphate, unlike calcic compounds, do not subsequently enter into
putrefaction.
Efforts are being made to convince manufacturers of the mistake in
using decanting vats, in connection with first and second
carbonatation. In Germany filter presses are used, decanting vats are
obsolete. The main objection to them is cooling of saccharine liquors,
which means an ultimate increase in fuel. Cooling is frequently
followed by partial fermentation.
Further changes in the proposed combined baryta-soda method for juice
purification consist in using powdered soda carbonate 90-92 deg.
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