e., turns blue; now
the solution of carbonate of soda is added and again stirred well.
After twenty or thirty minutes (the hotter the water, the quicker the
precipitation) the precipitate has settled in large flocks at the
bottom, and the clear water is drawn off into the pure water reservoir.
The precipitating and settling of the impurities can also take place in
cold water; it will require, however, a pretty long time.
In order to avoid the weighing and slaking of the lime, which is
necessary for each precipitation, we use an open barrel, in which a
known quantity of slaked lime is mixed with three and a half or four
times its weight of water, and then diluted to a thin paste, so that one
kilogramme slaked lime is diluted to twenty-five liters milk of lime.
Example.--If we use for ten cubic meters water, one kilogramme lime,
or in one day (in twenty-four hours), 240 cubic meters 24 kg. lime, a
vessel four or five feet high and about 700 liters capacity, in which
daily 24 kg. lime with about 100 liters water are slaked and then
diluted to the mark 600, constantly stirring, 25 liters of this mixture
contain exactly 1 kg. slaked lime.
Before using, this milk of lime has to be stirred up and allowed to
settle for a few seconds; and then we draw off the required quantity of
milk of lime (in our case 25 liters) through a faucet about 8 inches
above the bottom, or we can dip it off with a pail.
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