THE SPEAKER OF THE HOUSE OF COMMONS.

THE MASTER of the ROLLS.

THE LORD CHIEF JUSTICE OF HIS MAJESTY'S COURT OF COMMON PLEAS.

THE LORD CHIEF BARON OF HIS MAJESTY'S COURT OF EX

CHEQUER.

THE VICE PRESIDENT OF THE COMMITTEE OF COUNCIL FOR

TRADE.

THE RIGHT HON. SIR JOSEPH BANKS, BART. K. B.

THE RIGHT HON. SIR WILLIAM WYNNE.

THE RIGHT HON. SYLVESTER DOUGLAS.

INTRODUCTION.

THE Lords of the Committee of his Majesty's most honourable Privy Council, appointed by his Majesty, on the 10th of February, 1798, to take into consideration the state of the coins of this kingdom, having among other circumstances remarked the considerable loss which the gold coin appeared to have sustained by wear within certain periods, and being desirous to ascertain whether this loss was occasioned by any defect, either in the quality of the standard gold or in the figure or impression of the coins, were pleased to request that HENRY CAVENDISH, Esq. F. R. S. and myself would examine, by such experiments as should be deemed requisite, whether any of these defects really existed.

Two questions were to be principally decided,

1st. Whether very soft and ductile gold, or gold made as hard as is compatible with the process of coining, suffers the

most by wear, under the various circumstances of friction to which coin is subjected in the course of circulation?

2dly. Whether coin with a flat, smooth, and broad surface, wears less than coin which has certain protuberant parts raised above the ground or general level of the pieces?

Concerning the first question, opinions were various, and the most intelligent persons were uncertain whether very soft or hard gold was to be preferred; and, in respect to the second question, it must be observed, that although the prevalent opinion was in favour of flat and smooth surfaces, yet, as the fact had never been fully and satisfactorily determined, this opportunity was embraced, in order that every doubt might be removed.

The great value of the material, had hitherto prevented private individuals from ascertaining these facts by experiment; and, as a public concern, this subject of investigation, although so important to political economy and to science, does not appear to have been noticed by any European government, until the Right Honourable and enlightened Members of the abovementioned Committee proposed the inquiry, and furnished the requisite means for making the experiments.*

At the request of Mr. CAVENDISH, I have written the following account; but I should be highly unjust and ungrateful to that gentleman, did I not here publicly acknowledge how great a portion truly belongs to him, of any merit which these experiments may be found to possess: for, at all times, I was favoured with his valuable advice; and the machines to produce friction, as well as the dies, were entirely contrived by himself. At the These experiments were begun in the latter end of 1798, and were completed in April, 1801.

same time, I wish it to be understood, that I alone am to be considered as responsible for any inaccuracies of the experi

ments.

Lastly, before I proceed, I must take this opportunity to acknowledge my obligations to JAMES MORRISON, Esq. the Deputy Master of the Mint, to Mr. JAMES MORRISON, his son, to ROBERT BINGLEY, Esq. his Majesty's Assay Master, and to Messrs. ATKINSON and NICHOLL, of the Corporation of Moneyers, for the ready assistance and polite attention which I received from those gentlemen, during the long series of experiments made at the Mint.

SECTION I.

ON THE VARIOUS ALLOYS OF GOLD.

The wear of coin is an effect produced by mechanical causes, subject to be modified by certain physical properties, such as ductility and hardness, which vary in degree, according to the chemical effects produced by different metallic substances, when employed in certain proportions as alloys. From these considerations, it appears proper,

First, to examine the effects which the various metals produce upon gold, when combined with it in given proportions, beginning with, which is the standard proportion of alloy, and in certain cases gradually decreasing to of a grain in the ounce Troy, or 120 part of the mass.

I

Secondly, to examine the specific gravity of gold differently alloyed, and the causes of certain variations to which it is liable. And, thirdly, to ascertain the effects of friction variously modified.

GOLD ALLOYED WITH ARSENIC.

Experiment 1.

Eleven ounces one pennyweight and three grains (=5307 grs.) of gold, 23 carats 31grs. fine, being completely melted, eighteen pennyweights and twenty-one grains (=453 grs.) of pure metallic arsenic were added, and the whole being rapidly stirred, was quickly poured into a greased mould of iron.

The bar was of the colour of fine gold, and, although brittle, yet it bent in some measure before it broke. It weighed eleven ounces one pennyweight and nine grains; so that, of 18 dts. 21 grs. of arsenic, only six grains remained in combination with the gold; consequently, 18 dts. 15 grs. had been volatilized.

Experiment 11.

As the fine gold, in the foregoing experiment, retained so very small a portion of the arsenic, it appeared possible that copper might assist to fix that volatile substance.

To eighteen pennyweights and ten grains of the fine gold in fusion, nineteen grains of pure copper were added, being half the weight of the standard proportion of alloy.

When the copper was perfectly melted, and, by stirring, had been well incorporated with the gold, the crucible was removed, and at that moment mineteen grains of arsenic were added, and being quickly stirred, the metal was immediately poured into a mould.

The time which elapsed from the raising of the crucible to the pouring of the metal, was rather less than one minute; but, upon weighing the ingot, it appeared that the whole of the 19 grains of arsenic had been volatilized; and this was

corroborated by the perfect ductility which the gold was found to possess.

In this experiment, the whole of the arsenic was separated; and we may conclude, that it is always difficult to combine arsenic with gold by mere addition in open vessels, and that when to a small quantity of gold in fusion, a small quantity of arsenic is added, it is immediately dissipated by the violence of the heat; but, if large quantities are employed, and the metal is poured as soon as possible after the addition of the arsenic, then, according to circumstances, a small portion may remain combined with the gold.

It is well known that arsenic may be easily combined with gold and other metals, when in fusion, by employing a mixture of oxide of arsenic and black flux, and performing the operation in close vessels; but the following experiment will prove, that arsenic may at all times be combined with gold, provided the latter, when it loses its heat and congeals, is surrounded by arsenical vapour.

Experiment III.

480 grains of fine gold were put into a four-inch crucible, which was then placed within a large one that measured about 12 inches. At the bottom of this last, and on the outside of the small crucible, one ounce of metallic arsenic was placed, and another large crucible was then closely luted, with its mouth inverted upon that of the lower one.

The whole was exposed to a strong heat in a wind-furnace, during two hours, after which, the vessels were suffered gradually to become cold. Upon removing the upper crucible, which formed the dome, some white oxide of arsenic was found adhering to the inverted bottom of it.