While this is ftanding, put into a bafon two ounces of quick
lime, and an ounce o f orpiment; pour upon them a pint and a
half of boiling water; ftir the whole together, and when it has
flood a day and night, it will be fit for ufe. This is the liquor
probatorius vini o f fome of the German chemifls : it difcovers
lead when wines are adulterated with it, and will fhew it any
where.
Put a little of this liquor in a tea-cup, and plunge the piece of
rind half-way into it. .
In the former part o f this experiment, the veffels o f the rind
have been filled with a folution o f lead, that makes o f itfelf no
vifible alteration in them ; but this colourlefs impregnation, when
the orpiment lixivium gets to it, becomes of a deep brown; the
• veffels themfelves appear fomewhat the darker for it; but thefe
dots, which are real openings, now are feen to be plainly fuch,
the colour being perfeftly vifible in them, and much darker than
in the veffels. This object muft be always viewed dry.
I f a piece o f the rind, thus impregnated, be gently rubbed
between the fingers, till the parts are feparated, we fhall be able
in one place or other to get a view o f the veffels all round, and of
the films which form the blebs between them.
Every part of the rind, and every coat o f it, even the inter-
flitial place between it’s innermoft coat and bark, are filled with a
fine fluid. The very courfe and progrefs o f the fluid may be
fhewn in this part, even by an eafy preparation : only that
different rinds muft be fought for this purpofe, the veffels in fome
being
being larger than in others. Repeated trials have fhewn me that
the whole progrefs may beeafily marked in the three following
kinds, with only a tinfture of cochineal.
Put half an ounce o f cochineal, in powder, into half a pint of
fpirit o f wine; fet it in a warm place, and fliake it often for four
days ; then filter off the clear tin&ure. Put an inch depth of
this into a cup, and fet upright in it pieces o f the rind of afh,
white willow, and ozier, prepared as has been direfted, by maceration
in water; for in that way one trouble does for a hundred
kinds. Let an inch of the rinds alfo ftand up out o f the tinfture.
After twenty-four hours take them out, clip off the part which
was immerfed in the fluid, and fave the reft for obfervation.
T o PREPARE THE B lEA.
Cut the pieces in a fit feafon, either juft before the firft leaves
o f Spring, or in the midfummer (hooting time. Then we fee all
the wonders o f the ftrufture; the thoufands of mouths which
open throughout the courfe o f thefe innumerable veffels, to pour
their fluid into the interftitial matter.
Thefe veffels, which are in nature ciftems of fap for the feeding
the growth of the whole tree, are fo large, that they are
capable o f being filled with coloured wax, in the manner o f the
veffels in anatomical injeftions ; and this way they afford pfeafing
objects for the microfcope, and give excellent opportunities o f
tracing their courfe and flru&ure.
W A Method