[60] The representation of this apparatus, Pl. IV. Fig. 1. will convey a
much better idea of its disposition than can possibly be given by the
most laboured description.--E.
CHAP. VII.
_Of the Composition and Application of Lutes._
The necessity of properly securing the junctures of chemical vessels to
prevent the escape of any of the products of experiments, must be
sufficiently apparent; for this purpose lutes are employed, which ought
to be of such a nature as to be equally impenetrable to the most subtile
substances, as glass itself, through which only caloric can escape.
This first object of lutes is very well accomplished by bees wax, melted
with about an eighth part of turpentine. This lute is very easily
managed, sticks very closely to glass, and is very difficultly
penetrable; it may be rendered more consistent, and less or more hard or
pliable, by adding different kinds of resinous matters. Though this
species of lute answers extremely well for retaining gasses and vapours,
there are many chemical experiments which produce considerable heat, by
which this lute becomes liquified, and consequently the expansive
vapours must very readily force through and escape.
For such cases, the following fat lute is the best hitherto discovered,
though not without its disadvantages, which shall be pointed out. Take
very pure and dry unbaked clay, reduced to a very fine powder, put this
into a brass mortar, and beat it for several hours with a heavy iron
pestle, dropping in slowly some boiled lintseed oil; this is oil which
has been oxygenated, and has acquired a drying quality, by being boiled
with litharge. This lute is more tenacious, and applies better, if amber
varnish be used instead of the above oil. To make this varnish, melt
some yellow amber in an iron laddle, by which operation it loses a part
of its succinic acid, and essential oil, and mix it with lintseed oil.
Though the lute prepared with this varnish is better than that made with
265