ncentrated action of sulphuric acid, which
will dissolve all resins except caramba wax.

=Pumice-stone.=--This well-known light and spongy volcanic substance is
extensively quarried in the small islands that lie off the coast of
Sicily. Its porosity and smooth-cutting properties render it of great
value to painters and polishers for levelling down first coatings.
Ground pumice-stone is the best for cutting down bodies of polish or
varnish that are more advanced towards completion. The best way to get a
surface to a piece of lump pumice-stone is to rub it down on a flat York
stone, or, better still, an old tile that has been well baked.
Pumice-stone should not be allowed to stand in water; it causes the
grain to contract and to harden, thereby deteriorating its cutting
properties.

=Linseed-oil.=--This valuable oil is obtained by pressure from the seed
of the flax plant (_Linum usitatissimum_). Linseed contains on an
average about 33 per cent. of oil, though the amount varies materially,
the percentage obtained fluctuating considerably, not being alike on any
two successive days. This is partly due to the varying richness of the
seed, and partly to the manner in which it is manipulated in extracting
the oil, it being a very easy matter to lose a considerable percentage
of the oil by a lack of skill in any of the processes, though they all
seem so simple.

The first thing done with the seed from which the oil is to be extracted
is to pass it through a screen, to cleanse it from foreign substances.
The seed is received in bags containing from three to four bushels, and
pockets containing one-sixth of that amount. Having been screened it is
passed through a mill, whose large iron-rollers, three in number, grind
it to a coarse meal. Thence it is carried to what are known as the
"mullers," which are two large stones, about eight feet in diameter and
eighteen inches thick, weighing six tons each, standing on their edges,
and rolling around on a stone bed. About five bushels of the meal are
placed in the mullers, and about eight quarts of hot water are added.
The meal is afterwards carried by machinery to the heaters, iron pans
holding about a bushel each. These are heated to an even temperature by
steam, and are partly filled with the meal, which for seven minutes is
submitted to the heat, being carefully stirred in order that all parts
may become evenly heated. At the end of that time the meal is placed in
bags, which