providing air spaces between the outer and inner facings. The space between
the parts of the wall may be filled with materials that further retard the
loss of heat if this is necessary under the conditions prevailing.

_Residue From Generators._--The sludge remaining in the carbide to
water generator may be drawn off into the sewer if the piping is run at a
slant great enough to give a fall that carries the whole quantity, both
water and ash, away without allowing settling and consequent clogging.
Generators are provided with agitators which are operated to stir the ash
up with the water so that the whole mass is carried off when the drain cock
is opened.

If sewer connections cannot be made in such a way that the ash is entirely
carried away, it is best to run the liquid mass into a settling basin
outside of the building. This should be in the form of a shallow pit which
will allow the water to pass off by soaking into the ground and by
evaporation, leaving the comparatively dry ash in the pit. This ash which
remains is essentially slaked lime and can often be disposed of to more or
less advantage to be used in mortar, whitewash, marking paths and any other
use for which slaked lime is suited. The disposition of the ash depends
entirely on local conditions. An average analysis of this ash is as
follows:

Sand....................... 1.10 per cent.
Carbon..................... 2.72 "
Oxide of iron and alumina.. 2.77 "
Lime....................... 64.06 "
Water and carbonic acid.... 29.35 "
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