The works of the Honourable Robert Boyle, Esq., epitomiz'd by Richard Boulton ... ; illustrated with copper plates.

The third Section. Representing the uses of this Instrument, as re∣lating to Metals.

The first Ʋse.

Is to distinguish true Guineas from Counter∣feit.

The second Ʋse.

In examining a piece of Gold lighter than a Guinea; so much Ballast may be added as will make that amount to the weight of a Guinea, and if the Gold be heavier, so many of the perforated Plates must be taken off the Stem, that the Instrument may not be sunk by it, and when a Coin but a little heavier than a Guinea is to be tryed, it may be convenient to place a perforated Plate upon the upper screw, so that it may lye upon the Ball, and be taken off, or lightned with a file as occasion re∣quires.

That several pieces of Gold may upon some occasions be fix'd at once, the aperture of the screw ought to be wider, than what will just admit of a Guinea.

If the Instrument be well proportioned, so that a piece of Gold a little heavier than a Guinea, may not depress it under Water; it may be examined without altering the weight of the Instrument.

And acording to the method above laid down, a half Guinea may be tryed by placing a true half Guinea with it in the screw.

The third Ʋse.

This Instrument may be adjusted to try Sil∣ver Coins which are lighter than half a Crown, by weighing Silver in it, and marking the Sur∣face of the Water upon the Pipe, and then observing what difference there is betwixt that, and an equal weight of an ignobler Me∣tal in the Air. And tho' several Instruments would be more convenient for the trying of these different Metals, yet by altering the Ballast Plates, one may be made to serve the turn.

The fourth Ʋse.

And by the like method an Instrument may be adjusted, to discover whether Tin be more or less adulterated with Lead, since Tin being the lightest of Metals, the Lead will depress the Instrument lower if mixed with Tin, as Gold on the contrary is the heaviest Metal, and is lighter upon the addition of another Metal.

The fifth Ʋse.

It may enable us to guess at the Qualities of Metalline Mixtures, and the proportions of the ingredients, for by adjusting how much such a weight of Gold will depress the Stem, by af∣terwards trying how much lighter in Water

the same weight of allayed Gold in the Air will be, and at the same time observing what was the proportion of Silver in the Alloy, we may be enabled to judge how much other pieces of Gold are alloyed by comparing their weight in Water with this Standard, provided they be of the same specifick weight in the Air, with the Gold unalloyed. And the same mea∣sures may be taken to make an estimate of the alloys of Silver with Copper, or of Copper with Tin.