The arrangement here described is one that may readily be adapted to,
and is specially suited for, the old fashioned stills which are in
frequent use among pharmacists for the purpose of distilling water.
The idea is extremely simple, but I can testify to its thorough
efficiency in actual practice. The still is of tinned copper, two
gallon capacity, and the condenser is the usual worm surrounded with
cold water.
The overflow of warm water from the condenser is not run into the
waste pipe as in the ordinary course, but carried by means of a bent
tube, A, B, C, to the supply pipe of the still. The bend at B acts as
a trap, which prevents the escape of steam.
[Illustration]
The advantages of this arrangement are obvious. It is perfectly
simple, and can be adapted at no expense. It permits of a continuous
supply of hot water to the still, so that the contents of the latter
may always be kept boiling rapidly, and as a consequence it condenses
the maximum amount of water with the minimum of loss of heat. If the
supply of water at D be carefully regulated, it will be found that a
continuous current will be passing into the still at a temperature of
about 180° F., or, if practice suggest the desirability of running in
the water at intervals, this can be easily arranged. It is necessary
that the level at A should be two inches or thereabout higher than the
level of the bend at C, otherwise there may not be sufficient head to
force a free current of water against the pressure of steam. It will
also be found that the still should only contain water to the extent
of about one-fourth of its capacity when distillation is commenced, as
the water in the condenser becomes heated much more rapidly than the
same volume is vaporized. By this expedient a still of two gallons
capacity will yield about half a dozen gallons per day, a much greater
quantity than could ever be obtained under the old system, which
required the still to be recharged with cold water every time one and
a half gallons had been taken off.
The objection to all such continuous or automatic arrangements is, of
course, that the condensed water contains all the free ammonia that
may have existed in the water originally, but it is only in cases
where the water is exceptionally impure that this disadvantage will
become really serious. The method here outlined has, no doubt,
occurred to many, and may probably be in regular use, but not having
seen any previous mention of the idea, I have thought that it might be
useful to some pharmacists who prepare their own distilled
water.--_Phar. Jour._
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