visible; and upon little furnaces with equal degrees of heat, that their differences may be the more exactly noted. The fire also must be gentle; because when vehement, it hurries on and confounds the actions of bodies*.

HISTORY.

1. There are numerous bodies, not of a liquid, but solid consistence, that by heat acquire a degree of fluidity, so long as the heat continues to agitate and expand them; such as wax, suet, butter, pitch, rosin, gums, honey, lead, gold, silver, brass, copper, &c. though they require not only very different degrees of heat to open them; but also different modifications of the fire and flame. For some metals melt over a common fire; as lead: others require a fire animated by bellows; as gold and silver; and others again, the admixture of certain matters. So steel does not melt without the addition of some sulphureous body.

2. But if the fire be continued brisk and strong, all these substances not only open by colliquation; but also undergo a second opening, as that of volatility and waste, except gold alone. Quicksilver, which is a natural fluid, begins with this second kind of opening; and is easily vola

*A complete table of this kind is still wanting and should be derived from express chemical experiments.

tilized. But with regard to gold, it still remains a question, whether it can be rendered volatile, pneumatical, or potable, as they call it; that is, not soluble, as by means of aqua-regia, which is a common and obvious operation; but digesta» ble, or alterable by the human stomach. And the genuine criterion of this change is not, that the gold becomes volatile in the fire; but so subtile and attenuated as to be irreducible to metal again.*

3. Let farther enquiry be made about glass and vitrified bodies, whether they are consumable by fire, and convertible into pneumatical bodies for glass is accounted a fixed and juiceless body; and vitrification the destruction of metals.+

:

4. All bodies capable of fusion, begin the process of it from the lowest degree of opening; viz. softness, and suppleness, before they melt and run; such as wax, gums, metals, glass, &c.

5. But iront and steel, when perfectly purified and unmixed, bear a simple fire, without proceeding farther than to a degree of softness; so

* This point seems not hitherto settled to general satisfaction.

+ But improperly, as metals are easily recoverable from their glasses.

Viz. hammered iron.

as to become malleable and flexible, but not fusible, thereby.

6. Iron and glass, when opened to the abovementioned degree of softness, seem to be dilated in their included spirit; whence their tangible parts are so wrought, as to lay aside their hardness, and resistance; though the whole body is not, at the same time, visibly dilated, or swelled. But upon an exact enquiry: there will be found a certain invisible tumefaction, and agitation of parts therein; though this be restrained by their close and compact nature. For if thoroughly ig nited glass be laid upon a stone table, or other the like body, though well heated before hand; the glass will break, through the hardness of the stone resisting its secret tumefaction: aud there. fore, in taking glass out of the melting-pot, in order to blow it, they usually roll it upon some certain powder, or soft sand; which may gently give way, and not oppose this tumefaction in the parts of the glass.

7. Bullets likewise shot from a gun, after their projectile motion entirely ceases, so as that, to the eye, they shall seem perfectly at rest; yet a great shuddering motion, or pulsation, will be found, in their small parts, for a long while after: insomuch, that if any proper matter be laid upon them, it will thence receive and manifest a considerable force; and this proceeds not so much

from the burning heat, as from the tremor of percussion.

8. Rods of wood being fresh gathered, and kept turning in hot embers, acquire a softness; whence they may be bent at pleasure. And this experiment should be tried in old rods and canes.*

9. Combustible bodies open so, as by fire, first to emit a fume; then to take flame; and, lastly, fall into ashes,

10. Bodies which contain an aqueous moisture, that refuses the flame, and yet are close and compact; as bay-leaves, salts, &c. open by the fire in such a manner, that the aqueous and crude spirit they contain, being dilated by the heat, bursts out with a crackling noise, before they take flame: but if a body at once emits a flatulency, and takes flame, a violent tumult, and a powerful dilatation ensues; that flatulency, like bellows on the inside of the body, blowing and expanding the flame every way, as in der.

gunpow

11. Bread swells or rises somewhat in the oven; though it loses a little of its weight. And on the top of the loaf sometimes gathers a kind of crusty bubble, or bladder; so that there

* It has even been tried in large timbers for ship-building, with considerable success.

5

remains a cavity filled with air, between the pelicule of the crust, and the second surface of the loaf.

12. Roasted flesh also acquires a degree of tumefaction; especially when the outward skin is left upon it: as we see in roasted pigs, &c.

13. But roasted fruits sometimes leap out of the fire; as chesnuts: sometimes burst their skin, and spirt out their pulp; as apples: and if scorched by the fire, they acquire a burnt or scaly crust; and, as in the above-mentioned case of bread, leave a cavity between that crust and the flesh of the fruit. The same thing likewise happens in eggs.

14. But if the heat be slow, and without manifest fire, and there be also no ready vent for the vapour; as when pears are roasted in the warm ashes; and still more remarkably when the bodies to be treated are put into pots, and then buried under the ashes, or set in the oven, &c. in these cases the tumefaction or dilatation is repelled, by the heat, and turned back upon itself; whence ensues a condensation, as in distillation; and the body is more moistened, and, in a manner drowned with its own juice: as appears in pies, tarts, and other works of pastry and the oven.

15. But dry bodies, if the flame be suffocated and find no easy exit, become rarified, hollow,