boiled oil, yet, as its additional expence is hardly compensated by its
superior quality, it is seldom used.
The above fat lute is capable of sustaining a very violent degree of
heat, is impenetrable by acids and spiritous liquors, and adheres
exceedingly well to metals, stone ware, or glass, providing they have
been previously rendered perfectly dry. But if, unfortunately, any of
the liquor in the course of an experiment gets through, either between
the glass and the lute, or between the layers of the lute itself, so as
to moisten the part, it is extremely difficult to close the opening.
This is the chief inconvenience which attends the use of fat lute, and
perhaps the only one it is subject to. As it is apt to soften by heat,
we must surround all the junctures with slips of wet bladder applied
over the luting, and fixed on by pack-thread tied round both above and
below the joint; the bladder, and consequently the lute below, must be
farther secured by a number of turns of pack-thread all over it. By
these precautions, we are free from every danger of accident; and the
junctures secured in this manner may be considered, in experiments, as
hermetically sealed.
It frequently happens that the figure of the junctures prevents the
application of ligatures, which is the case with the three-necked
bottles formerly described; and it even requires great address to apply
the twine without shaking the apparatus; so that, where a number of
junctures require luting, we are apt to displace several while securing
one. In these cases, we may substitute slips of linen, spread with white
of egg and lime mixed together, instead of the wet bladder. These are
applied while still moist, and very speedily dry and acquire
considerable hardness. Strong glue dissolved in water may answer instead
of white of egg. These fillets are usefully applied likewise over
junctures luted together with wax and rosin.
Before applying a lute, all the junctures of the vessels must be
accurately and firmly fitted to each other, so as not to admit of being
moved. If the beak of a retort is to be luted to the neck of a
recipient, they ought to fit pretty accurately; otherwise we must fix
them, by introducing short pieces of soft wood or of cork. If the
disproportion between the two be very considerable, we must employ a
cork which fits the neck of the recipient, having a circular hole of
proper dimensions to admit the beak of the retort. The same precaution
266