one end of these tubes I fit a shall cyringe or pump, in such manner as to exhaust the air from both of the glass tubes at the same time with the saine cyringe or pump. Then the instrument becomes a double pump, or a pump with two parallel tubes, which are both exhausted by one piston. If water is drawn into both tubes it will rise to an equal height by the weight of atmosphere; but if a column of water is drawn into one tube, and a column of the highest rectified spirit into the other, the two columns will rise to different heights. The different length of these columns will be in exact proportion to their gravity; and this difference will determine the length of a scale which I graduate by actual experiment, by diluting the spirit one per cent. at a time, and repeating the experiment till the scale is finished. When it is finished it is fitted to the glass tubes near the cyringe, so as to apply like the scale of an hydrometer. On the other end of the instrument, a small vessel is fitted to receive the liquors. This vessel is separated into two equal parts by a partition, so that one part may be filled with water and the other with spirits, and both remain şeparate. This partition passes between the two glass tubes. When a sample of spirits is to be tried, one side of this vessel must be filled with water, and the other with the sample to be tried. Then it is drawn into the instrument till the water rises exactly to the bottom of the scale, and the spirits will then rise higher to the proof-mark, or above or be low, according to its strength. If a sample of spirits is tried in this instrument by another sample of known proof, the difference will appear on the scale without the assistance of the thermometer, because the state of the atmosphere affects both samples alike, or very nearly so. The size and proportions of this instrument may be varied at pleasure. Some of them are provided with a stopC 2

cock,

cock, for the purpose of more conveniently retaining the fluids in the instrument till the observation is made. This cock is fitted between the cyringe and the end of the glass tubes; and others are made with a cock instead of a cyringe; and then the instrument is exhausted by the mouth, and the cock is turned to retain the liquor in the instrument till the observation is made.

In witness whereof, &c.

Experiments and Observations on the various Alloys, or the Specific Gravity, and on the comparative Wear of Gold. Being the Substance of a Report made to the Right Honourable the Lords of the Committee of Privy Council, appointed to take into Consideration the State of the Coins of this Kingdom, and the present Establishment and Construction of IIis Majesty's Mint.

By CHARLES HATCHETT, Esq. F. R. S.

With a Plate.

Abstracted from the TRANSACTIONS of the ROYAL SOCIETY By Mr. DAVY, of the ROYAL INSTITUTION.

THIS abstract contains the result of a great number of accurate and laborious investigations on the properties of the alloys of gold. They were made at the request of the Lords of the Committee of his Majesty's most honourable Privy Council, appointed by his Majesty on the tenth of February, 1798, to take into consideration the state of the coins of the kingdom.

Mr. Hatchett was assisted in his researches by the valuable advice of Henry Cavendish, Esq. F, R. S. and the

machines

machines for ascertaining the wear of the coins were invented by that gentleman.

The full detail of the experiments, which occupied between two and three years labour, are inserted in the Phi losophical Transactions for 1803.

The principal object of the experiments was to ascertain, whether the great loss which our gold coin appears to have sustained within certain periods had really been caused, or had been materially influenced, by any impor tant defect, either in the quality of the standard gold, or in the figure or impression of the coin; but, in order to determine this, the decision of two questions became necessary; namely,

First. Whether very ductile gold, or gold as hard as is compatible with the process of coining, suffers the greatest loss, under the general circumstances of friction?

Secondly. Whether coins with flat, smooth, and broad surfaces, wear less or more, than coins which have certain protuberant parts raised above the ground or general level of the pieces?

It appeared, that neither of these questions had ever been decided by actual experiment, and the best informed persons were in every respect much divided in their sentiments; for some conceived hard, and others soft gold, to be the best for coin; and some in like manner believed, contrary to the general opinion, that the pieces which were flat and smooth were more susceptible of wear than those which had fewer points of contact in consequence of protuberances. As therefore nothing certain relative to these matters could be gained from books, nor from those who were consulted, the solution of the questions was attempted by the experiments which will now be described; and for this pur

pose

pose, the Lords of the Committee furnished the requisitë

means.

The wear or abrasion of coin is a mechanical effect, subject to be modified by certain physical properties, such as ductility and hardness; and as these last-mentioned properties in mixed or alloyed metals are much influenced, by chemical effects, which the different metals mutually produce upon each other, it naturally follows, that the experiments required to investigate the present subject must form three distinct series, in the first of which will be comprehended the chemical experiments, or those which relate to the effects produced upon gold by the addition of different metals in certain given and equal relative proportions.

The second series will include the experiments which relate to the different degrees of density observed in gold when variously alloyed; and, as the specific gravity of standard and other gold has always been regarded as one of the most certain tests of its quality, exclusive of chemical analysis, it appears to be of much importance to ascertain how far this can with certainty be depended upon; and how far, and from what causes, it is liable to unavoidable and occasional variations.

The third and last series consists of those experiments which may be called mechanical, and which were expressly intended to ascertain the comparative wear of different kinds of gold, by various modes of friction.

The account of the whole of these experiments has therefore been digested into three separate parts, corresponding to the three principal series which have been mentioned.

SECTION

SECTION I.

A. From the various experiments made with arsenic and gold, in open and close vessels, it appears, that arsenic combines with gold only under certain circumstances; but when united with it, then the colour and ductility of gold become considerably affected, and the arsenic (although naturally volatile) cannot easily be completely separated, even by long-continued fusion,

B. Antimony more readily combines with gold, under all general circumstances; and it is proved, by the experiments, that of a grain of antimony in the ounce Troy, or the 19 part of the mass, is sufficient to destroy the ductility of gold.

c. Zinc, whether alone, or mixed with copper in the state of brass, also destroys the ductility of gold; but it is easily separated by heat.

D. Cobalt affects the colour and malleability of gold, until the proportion is reduced to four grains per ounce; the effects of it then begin to cease.

E. Nickel is not so injurious to gold as the foregoing metals, as four grains did not produce any remarkable effect; and there is reason to believe, that of all those which are improperly called semimetals, nickel is that which is the least prejudicial to gold.

F. Manganese changes the colour, and considerably injures the ductility of gold,

G. Bismuth is highly destructive of the general properties of gold; for the vapour of it affects that metal even when melted in open vessels. Like antimony, a very small proportion of bismuth, such as part, is sufficient to render gold completely brittle.

H. The effects of lead upon gold resemble those of bismuth in every particular.