A continuation of new experiments physico-mechanical, touching the spring and weight of the air and their effects. The I. part whereto is annext a short discourse of the atmospheres of consistent bodies / written by way of letter to the right honourable the Lord Clifford and Dungarvan by the honourable Robert Boyle ...

EXPERIMENT XXI.

Of the Heights at which pure Mercury, and Mercury Amal∣gam'd with Tin, will stand in Barometers.

COnsidering with my self, that if the Sustentation of the Quick-silver in the Torricellian Experiment at a certain height, depends upon the Aequilibrium, which a Liquor of that Specifick Gravity does at such a height attain to with the Exter∣nal Air, if that peculiar and determinate Gravity of the Quick-silver be altered, the height of it, requisite to an Aequilibrium with the Atmosphere, must be altered too: (Considering this I say) I thought it might somewhat confirm the Hypothesis hitherto made use of, if a Phaenomenon so agreeable to it were actually exhibited. This I supposed performable two differing wayes, namely by mixing or (as Chymists speak) Amalgamating Mercu∣ry either with Gold, to make it a mixture more heavy, or with some other Metal that might make it more light than Mercury alone is. But the former of those two ways I forbore to prose∣cute being where I then was unfurnished with a sufficient quantity of refined Gold, (for that which is Coyn'd is generally allayed with Silver, or Copper, or both,) and therefore Amalga∣mating Mercury with a convenient proportion of pure Tin, (or, as the Tradesmen call it, Block-Tin,) that the mixture might not be too thick to be readily poured out into a Glass-Tube, and to subside in it, we fill'd with this Amalgam a Cylindrical Pipe, sea∣led

at one end, and of a fit length, and then inverted it into a litle Glass furnished with the like mixture. Of which Tryal the E∣vent was, that the Amalgam did not fall down to 29, nor even to 30 inches, but stopt at 31 above the surface of the stagnant Mix∣ture.

Note 1. That though one may expect, that the Event of the Experiment would be the more considerable, the Greater the Quantity is that is mingled of the light Metal, yet care must be taken that the Amalgam be not made too thick, least part of it stick here and there (as we did to our trouble find it apt to do) to the inside of the Pipe, by which means some Aerial Corpu∣scles will meet with such convenient Receptacles, as to make it very difficult, if not almost impossible, to free the Tube quite from Air.

2. It may perhaps be worth while to try, whether by compa∣ring the height of the Amalgam, to what it ought to be upon the score of the specifick Gravities of the Mercury, and the Tin, min∣gled in a known Proportion in the Amalgam, any discovery may be made whether those two Metals do penetrate one another after such a manner (for there is no strict Penetration of Dimensi∣ons among Bodies) as Copper and Tin have, as I elsewhere note, been (by some Chymists) observ'd to do, when being melted down together they make up a more close and specifically ponde∣rous Body, than their respective Weights seem'd to require.

3. That by comparing this 21. Experiment with the 18^th of those formerly published, it may appear, that the height of the Liquor, suspended in the Torricellian Experiment, depends so much upon its aequilibrium with the outward Air, that it may be varied by a change of Gravity in either of the two Bodies that counterballance each other, whether the change be of weight in the Atmosphere, or of Specifick Gravity in the suspended Liquor.