But if the generating flask
is employed, water is allowed to drop from the tap-funnel on to the
carbide in the flask at the rate of 6 to 7 drops a minute (the tap-funnel
being filled up from time to time), and all the carbide will thus be
decomposed in 3 to 4 hours. The flask is then filled to the neck with
water, and disconnected from the absorption apparatus, through which a
little air is then drawn. The absorbing liquid is then poured, and washed
out, into a beaker; hydrochloric acid is added to it, and it is boiled in
order to expel the liberated chlorine. It is then usual to precipitate
the sulphuric acid by adding solution of barium chloride to the boiling
liquid, allowing it to cool and settle, and then filtering. The weight of
barium sulphate obtained by ignition of the filter and its contents,
multiplied by 0.137, gives the amount of sulphur present in the acetylene
in the form of sulphuretted hydrogen. The filtrate and washings from this
precipitate are rendered slightly ammoniacal, and a small excess of
"magnesia mixture" is added; the whole is stirred, left to stand for 12
hours, filtered, the precipitate washed with water rendered slightly
ammoniacal, dried, ignited, and weighed.
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