The specific gravity of another piece of cork was.241, or about 4 times lighter than water.

N. B. In weighing of thofe bodies whofe pores readily imbibe the water, the quicker the experiment is performed, the more likely it is to be

correct.

METHOD OF FINDING THE SPECIFIC GRAVITY OF FLUIDS.

That which is meant by the term Specific gravity of bodies, being nothing more than the difference, or comparative weight of those bodies to that of common water, we might eafily find the fpecific gravity of any kind of fluid, by weighing a quantity of it against an equal quantity of water; but as a folid body, when immerfed in a fluid, lofes as much of it's weight as a bulk of the fluid equal to the body weighs, a more convenient and accurate method is the immerfion of a folid, of fome determinate weight, in the fluid whofe fpecific gravity we defire to know.

For this purpose is the conical piece of folid glafs, belonging to the hydrostatic ballance; whose weight, both in air and in water, being known, fhews immediately the weight of the fluid into which it is fufpended; the folid being borne up by the fluid in a proportion equal to it's refpective gravity.

Suppofe the glafs folid to weigh in air 1464 grains, and that, when it is fufpended from the water-scale, and immerged in water, it lofes of it's weight 445 grains; this would be the weight of a bulk of water equal to the folid. The ballanceweight for the folid must be made juft equal to what it weighs in water, i. e. 1019 grains.

Whatever fluid is to be weighed, let it be put into the glass recipient; fufpend the folid to the

Ee 3

hook

hook of the water-fcale, and let it hang freely in the liquor, putting the ballance-weight in the oppofite fcale. If the fluid be heavier than water, the folid will rife in it; if lighter, it will fink to the bottom of the recipient. In either cafe fmall weights are to be put into the lighter fcale, till the ballance be made even.

1. When the fluid is lighter than water, the weight gained by the glass solid is to be fubtračled from the weight of a bulk of water equal to the folid [445], and the remainder is the weight of an equal bulk of the fluid, or it's fpecific gravity to

water.

Example 1. When fuch a glafs folid as the above was immerfed in brandy, it ballanced 38.2 grains more than in water. This, taken from 445.0, leaves 406.8; therefore the specific weight of the brandy was to water as 406.8 to 445.

To reduce it to it's proper terms, multiply the difference [38.2] by 1000, (the denominator of water) and divide the product by 445. As 445 38.2 1000: 86; fubtract 86 from 1000, there remain .914, the specific gravity of the brandy.

From hence it appears, that the brandy weighed 86 parts in 1000, or about less than

water.

Example 2. In rum the folid ballanced 40.3 grains more than in water; as 445: 40.3:: 1000:91 --91 from 1000, remain .909. The fpecific gravity of the rum to water was therefore .909, or about.

Example 3. When the folid was immerfed in highly rectified Spirit of wine, it ballanced 73.6 more than in water; therefore 445: 73.6:1000: 165. 165 from 1000, remain .835, or 1.

It appears from thefe examples, that the by

droftatic

drostatic ballance is a certain and correct inftrument for determining the frength of Spirits, perhaps more fo than the most accurate hydrometer that has yet been made for that purpose.

It is of confiderable confequence to diftillers, and dealers in fpirituous liquors, to know the precife point of ftrength which is termed proof: though this, indeed, is rather arbitrary, than any fixed ftandard; but the degree of ftrength which, I am informed, is now called merchantable proof, fixeth the specific gravity of the spirit to water at .930.

:

930 taken from 1000 leaves 70; therefore 1000: 70: 445 31.15. So that in proof Spirit, a glafs folid of the weight above-mentioned, muft ballance 31.15, or about 31 grains more than in

water.

It may easily be found in what proportion the fpirit is above or below proof, by obferving what quantity of water or alcohol is neceffary to be mixed with it, in order to bring it to the above ftandard; and it might be immediately known, by comparing the weight of the fpirit with that of water, if the fpecific gravity of both, when compounded, remained in the fame ratio as when feparate; but as it is found that, when water is mixed with fpirit, the fpecific gravity of the compound is greater than that of the water and the fpirit before they are compounded, the calculation must therefore turn out incorrect. For inftance,

A quantity of the rum, before-mentioned, equal in bulk to the glafs folid, weighed very nearly 405 grains, an equal bulk of water 445 grains; fuppofe, then, that in order to reduce the rum to proof, one fifth part of water was to be mixed with it;

By this it appears, that a quantity of the compound, equal in bulk to the glafs folid, fhould weigh 413 grains, and confequently that the folid, when immerfed in it, fhould ballance 32 grains more than in water; in which cafe it would ftill be fomewhat above proof.

But, upon trial, it will be found to ballance not much more than 291, and that there must be but little more than one-feventh part of water mixed with the rum to reduce it to the given standard.

Immediately after water is mixed with fpirit, the compound appears lighter; but in a few hours afterwards, when the particles of each are more intimately united, it's bulk diminishes, and confequently the fpecific gravity increases.

From a few experiments of this kind, the theory will appear fufficiently plain; and a table might eafily be formed for fhewing by inspection what quantity of water is neceffary to be put to any given quantity of fpirit, to render it true proof.

2. When fluids are fpecifically heavier than water, the glass folid, as before observed, will rise in fuch fluid (the water ballance-weight being in the oppofite fcale) and appear to be lighter; fmall weights are therefore to be put in the water-fcale, till the equilibrium be restored; and the lofs which the folid fuftains, by being weighed in the heavy fluid, is to be added to the weight of a bulk of water equal to the folid; the fum fhews the specific gravity of the fluid to water.

Example 4. Suppofe it was required to find

the

the specific gravity of fea-water, or how much heavier it is than rain-water.

Let the folid be fufpended, as ufual, to the water-scale, and immersed in the fea-water, putting the ballance-weight in the oppofite fcale. It will require 11.6 grains to bring it to an even ballance.

As 445 11.6 : 1000: 26.

The specific gravity is therefore 1026; which fhews that fea-water is 26 parts in 1000, or

heavier than rain-water; or that there must b 1026 measures of rain-water, to weigh as much as 1000 measures of fea-water. The method is the fame for every other fluid fpecifically heavier than

water.

The specific gravity of falt and water, in equal quantities (in measure) is 1205; or about one-fifth heavier than common water.

METHOD OF DISCOVERING THE PROPORTION OF ALLOY MIXED WITH GOLD.

The specific gravity of sterling or money gold, as before obferved, is 17.79, which is the ftandard made use of in the following calculations, as it comes the nearest to the average weight of the current British coin. The specific gravity of pure, or very fine gold, is indeed confiderably more; in fome tables it is made 19.64, but it is feldom met with fo heavy as this. The fpecific gravity of good filver is 10.37; of copper 8.83.

If, then, a mafs be compounded of gold and filver, the fpecific gravity of the compound may be thus found, without the use of the ballance.

Example 1. Suppose a mass of metal, half gold and half silver [in weight], to weigh in air 258.8

grains,