MRS. B.
By no means: they consist of nothing more than common sulphur, reduced to a very fine powder by a process called sublimation.—You see some of it in this phial; it is exactly the same substance as this lump of sulphur, only its colour is a paler yellow, owing to its state of very minute division.
EMILY.
Pray what is sublimation?
MRS. B.
It is the evaporation, or, more properly speaking, the volatilisation of solid substances, which, in cooling, condense again in a concrete form. The process, in this instance, must be performed in a closed vessel, both to prevent combustion, which would take place if the access of air were not carefully precluded, and likewise in order to collect the substance after the operation. As it is rather a slow process, we shall not try the experiment now; but you will understand it perfectly if I show you the apparatus used for the purpose. ([Plate XI.] fig. 1.) Some lumps of sulphur are put into a receiver of this kind, which is called a cucurbit. Its shape, you see, somewhat resembles that of a pear, and is open at the top, so as to adapt itself exactly to a kind of conical receiver of this sort, called the head. The cucurbit, thus covered with its head, is placed over a sand-bath; this is nothing more than a vessel full of sand, which is kept heated by a furnace, such as you see here, so as to preserve the apparatus in a moderate and uniform temperature. The sulphur then soon begins to melt, and immediately after this, a thick white smoke rises, which is gradually deposited within the head, or upper part of the apparatus, where it condenses against the sides, somewhat in the form of a vegetation, whence it has obtained the name of flowers of sulphur. This apparatus, which is called an alembic, is highly useful in all kinds of distillations, as you will see when we come to treat of those operations. Alembics are not commonly made of glass, like this, which is applicable only to distillations upon a very small scale. Those used in manufactures are generally made of copper, and are, of course, considerably larger. The principal construction, however, is always the same, although their shape admits of some variation.
Vol. I. p. 237.
Fig. 1. A Alembic. B Sand-bath. C Furnace.
Fig. 2. Eudiometer.
Fig. 3. A Retort containing water. B Lamp to heat the water. C.C Porcelain tube containing Carbone. D Furnace through which the tube passes. E Receiver for the gas produced. F Water bath.