" It must also be remembered that
chemical processes which are perfectly suited to the extraction of
sulphuretted hydrogen and phosphine are not necessarily adapted for the
removal of the other phosphorus and sulphur compounds.
WASHERS.--In designing a washer for the extraction of ammonia and
sulphuretted hydrogen it is necessary to see that the gas is brought into
most intimate contact with the liquid, while yet no more pressure than
can possibly be avoided is lost. Subdivision of the gas stream may be
effected by fitting the mouth of the inlet-pipe with a rose having a
large number of very small holes some appreciable distance apart, or by
bending the pipe to a horizontal position and drilling it on its upper
surface with numbers of small holes. Another method is to force the gas
to travel under a series of partitions extending just below the water-
level, forming the lower edges of those partitions either perfectly
horizontal or with small notches like the teeth of a saw. One volume of
pure water only absorbs about three volumes of sulphuretted hydrogen at
atmospheric temperatures, but takes up some 600 volumes of gaseous
ammonia; and as ammonia always accompanies the sulphuretted hydrogen, the
latter may be said to be absorbed in the washer by a solution of ammonia,
a liquid in which sulphuretted hydrogen is much more soluble.
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