and porous: as we see in charcoal, and the pumice-stones discharged from burning mountains.

SECT. V.

OF DILATATIONS BY EXTERNAL HEAT, AND DISTILLATIONS.

THERE are two kinds of dilatation, opening, or attenuation, of bodies in distillations; the one in passage, when the body is turned into va→ pour or fume, which is afterwards restored; the other in the body so restored; which is always more rarified, more subtile and expanded than the crude body from whence it was distilled: as rose-water, for example, is more rarified and light, than the juice of roses.

All distillation is performed by a kind of flux and reflux, or alternate rarifaction and conden sation; the one raising the vapour, or rendering the body pneumatical; and the other striking it back, or restoring it to a tangible state.

The actions of dilatation and condensation, are not pure in the case of distillations; but the separation of heterogeneous parts intervenes : which is the intentional action with regard to practice; whereby the purer juices, the phlegm, the oil, the fine parts, and the gross parts of bodios are separated from each other.

Under distillations it is proper to enquire into, and determine, the degrees and diversities of heats; as that of coals, a hot oven, that of baths, that of water, ashes, sand, &c. that of the sun, horse-dung, fire left to itself, fire animated by bellows, fire confined and reverberated, heat ascending, heat descending, and the like; all which have a remarkable efficacy in the opening of bodies; and particularly in the complicate actions of dilatation and contraction. For these heats seem by no means to resemble the heat of the sun, and celestial bodies; neither in gentleness, softness, temperature, continuance, retraction, modification by intermediate bodies; nor in ebbing and flowing, with the remarkable inequality of day and night. But all these particulars should be diligently examined, under the general titles of heat and cold; with their subordinate divisions.*

Distillations, and the dilatations they cause, are performed in a close vessel; where the body to be distilled, the vapours it affords, and the air, are shut up together: for in the common stills and alembics, the external air is not excluded from entering, in some degree, the pipe of the still-head, or nose of the worm. But in retorts,

* See Mr. Boyle's History of Cold; and the Chapter of Fire in Dr. Boerhaave's Chemistry.

where a stronger heat is required, the external air has no entrance; the mouth of the receiver being joined by a luting to the neck of the retort; so that the whole process of rarifaction and condensation is performed within. But if the body be full of a vigorous spirit, as nitre or vitriol, it requires a capacious receiver; that the vapours may freely play about therein, without bursting the glass.

PRECEPTS.

1. But though distillations are performed, as it were in a close cell; yet there is still space enough allowed for some parts of the body to expand into vapour, and other parts to subside in fæces; and again, for the vapours to wind and roll about, restore themselves, and, when of different natures, to separate one from another. The following precept, therefore, is of the utmost importance; as it may advance a method of putting nature to the scrutiny, and producing new transformations: for the fire of the chemists and physicians, though it has produced many useful things; yet does not, perhaps, obtain the more genuine virtues, and properties of heat, by reason of the distractions and separations of the parts, which constantly happen in their operations. The sum of our precept, comes to this, that all separation, and all flux and reflux of rarification and condensation, be totally prohibit

ed; and that the heat be spent entirely within the body itself, and its cavities. Such a method may possibly hold the Proteus matter, bound and manacled, and compel it to try all its shapes and conversions, in order to free and clear itself. Numerous instances occur to us, with regard to this affair; and others may be discovered: but we will here propose only an easy example or two, the more fully to express our meaning.

2. Having provided a cubical vessel of iron, the sides whereof are very strong and thick; fit a cube of wood exactly to it, so as perfectly to fill the cavity: then, in the securest manner, fix and lute on a strong cover of the same metal, so as not to give the least vent; but remain capable of bearing the heat. Now place the vessel in the fire, and there continue it for some hours; afterwards take off the cover, and examine what change the wood has suffered. It should seem, that as the wood in this case, could neither flame nor emit a fume, so as to discharge any of its pneumatical or moist parts; the body of the wood must either be converted into a kind of amalgam; or resolved into air; that is, a truly pneumatical body; leaving at the bottom, certain feculent parts, grosser than ashes; and some incrustation on the sides of the vessel.*

*The experiment seems to have never been tried;on

3. Let trial also be made of a quantity of pure water, that shall perfectly fill a like kind of irònvessel: but here the fire should be more gentle; and the operation of longer continuance. The vessel also might be removed from the fire at certain hours; and afterwards put on again: and this for several times. We make choice of pure water for this experiment, because water is a simple body, without colour, smell, taste, or other remarkable qualities. And, therefore, if by a mild and gentle heat, an interchange of heating and cooling, and a prevention of all evaporation, the spirit of the water shall not be lost, but still be wrought upon, and become attenuated by this kind of heat, so as to turn itself upon the grosser parts of the water, and digest and change them into a new texture and arrangement, of greater simplicity and uniformity; the water thus acquiring either a different colour, smell, taste, a degree of oiliness, or any other considerable alteration, like what we find in compound bodies; doubtless it would prove a great acquisition, and open a way to numerous particulars of moment.*

account, perhaps, of the danger that may be apprehended from the bursting of the vessel. But any inconveniences of this kind might be prevented by an artist.

* Because it would then afford a practical instance of the transmutability of bodies." See the Sylva Sylvarum.