The fact that ordinary calcium carbide is attacked so quickly by
water is really a defect of the substance; for it is to this extreme
rapidity of reaction that the troubles of overheating are due. Now, if
the basket in the generator B^1 of Fig. 2, or, indeed, the carbide store
in any of the carbide-to-water apparatus, is filled with a carbide which
has been treated with oil or wax, as long as the water-level stands at
_l'_ and _l"_ or the carbide still remains in the hopper, it is
essentially unattacked by the vapour arising from the liquid; but
directly the basket is submerged, or the lumps fall into the water,
acetylene is produced, and produced more slowly and regularly than
otherwise. Again, oils do not mix with water, but usually float thereon,
and a mass of water covered by a thick film or layer of oil does not
evaporate appreciably. If, now, a certain quantity of oil, say lamp
paraffin or mineral lubricating oil, is poured on to the water in B^1,
Fig. 2, it moves upwards and downwards with the water. When the water
takes the position _l_, the oil is driven upwards away from the
basket of carbide, and acetylene is generated in the ordinary manner; but
when the water falls to _l"_ the oil descends also, rinses off much
of the adhering water from the carbide lumps, covers them with a greasy
film, and almost entirely stops generation till it is in turn washed off
by the next ascent of the water.
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