If, as should be done, the gas is passed through a washer or
condenser containing much water before it enters the holder the
sulphuretted hydrogen and ammonia will be extracted, and the seal will
not acquire an obnoxious odour for a very long time.
Four principal substances have been proposed for lowering the freezing-
point of the water in an acetylene-holder seal; common salt (sodium
chloride), calcium chloride (not chloride of lime), alcohol (methylated
spirit), and glycerin. A 10 per cent. solution of common salt has a
specific gravity of 1.0734, and does not solidify above -6 deg. C. or 21.2 deg.
F.; a 15 per cent. solution has a density of 1.111, and freezes at -10 deg.
C. or 14 deg. F. Common salt, however, is not to be recommended, as its
solutions always corrode iron and steel vessels more or less quickly.
Alcohol, in its English denatured form of methylated spirit, is still
somewhat expensive to use, but it has the advantage of not increasing the
viscosity of the water; so that a frost-proof mixture of alcohol and
water will flow as readily through minute tubes choked with needle-
valves, or through felt and the like, or along wicks, as will plain
water.
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