This assertion would appear to
require substantiation, but a patent has been taken out for a process of
drying the sludge at a temperature of 150 deg. to 200 deg. C. in order to
remove the harmful matter by the action of the steam evolved. So purified,
it is claimed, the lime becomes fit for treating any hard potable or
boiler-feed water. It is very doubtful, however, whether the intrinsic value
of acetylene lime is such in comparison with the price of fresh lime that,
with whatever object in view, it would bear the cost of any method of
artificial drying if obtained from the generators in a pasty state.
When, on the other hand, the residue is naturally dry, or nearly so, it
is exactly equal to an equivalent quantity of quick or slaked lime as a
dressing for soil. In this last connexion, however, it must be remembered
that only certain soils are improved by an addition of lime in any shape,
and therefore carbide residues must not be used blindly; but if analysis
indicates that a particular plot of ground would derive benefit from an
application of lime, acetylene lime is precisely as good as any other
description. Naturally a residue containing unspent carbide, or
contaminated with tarry matter, is essentially valueless (except as
mentioned below); while it must not be forgotten that a solid residue if
it is exposed to air, or a pasty residue if not kept under water, will
lose many of its useful properties, because it will be partially
converted into calcium carbonate or chalk.
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