In what Cases glass, or earthen Alembics are to be used; their Advantages and Disadvantages.
In the Chapter relating to Accidents, we have mentioned the earthen Alembic; we must now add, that it ought never to be used, except the Matter to be distilled have a strong and bad Smell, and then seldom above once, unless it be for Ingredients of the same or similar Qualities.
This Alembic being very difficult to be managed, we can only recommend it in the Case above-mentioned.
As a naked Fire is generally applied to this Alembic, it requires a Furnace where the Fire may be gradually increased, on account of the Accidents to which it is liable.
The glass Alembic is more easily managed, as it is generally placed in a Balneum Mariæ. Its principal Use is for distilling Waters from Flowers, and making Quintessences; and were it not for the Length of the Operation, it would be preferable to any other Method.
This Alembic hardly admitting of a Refrigerant, a wet linen Cloth must be placed on the Head, and often changed.
The Receiver of this Alembic must not be very large, because of the Fragility of the Bec; but if it were ever so little bent into a Curve, the Largeness of the Receiver would be of no Prejudice; because then its whole Weight would be supported by its Stand.
Advantages of Distillation performed by the Vapour Bath.
This Method differs very little from the Balneum Mariæ, and is used nearly in the same Circumstances; but has greatly the Advantage of the Balneum Mariæ in the Quickness of the Operation. And Lemery, in the first Part of his Course of Chemistry, affirms its Operation to be more perfect.
However that be, its Use is equal to that of the Balneum Mariæ; but in distilling sweet-scented Waters, or Flowers, Sand must be placed at the Bottom, that the Liquor may not contract a Taste from the Copper.