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Experiments and Observations on the various Alloys, on 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 Com- 

 mittee of Privy Council, appointed to take into Consideration the 

 State of the Coins of this Kingdom, and the present Establishment 

 and Constitution of His Majesty's Mint. By Charles Hatchett, 

 Esq. F.R.S. Read January 13, 1803. [Phil. Trans. 1803, p. 43.] 



From the introduction to this paper we learn, that in the year 1798, 

 His Majesty was pleased to appoint a committee of members of his 

 Privy Council, to take into consideration the state of the coins of the 

 kingdom ; and that this committee, having remarked the considerable 

 loss which the gold coin in particular had sustained by wear within 

 certain periods, had applied to Mr. Cavendish and Mr. Hatchett for 

 their opinion what were the causes of this diminution, and what 

 remedy might be applied to the defects by which it is occasioned. 

 The mode of carrying on this investigation having been agreed upon 

 by these two gentlemen, it fell to Mr. Hatchett's lot to perform the 

 preconcerted experiments, and to draw up the account of them. Of 

 this account, as it was too voluminous, and consisted of too many 

 tables to be read in public, Mr. Hatchett has been pleased to commu- 

 nicate to the Society the Abstract, the reading of which took up the 

 whole of this and the preceding meeting. On a general contemplation 

 of the subject, it soon occurred that the inquiry was to be directed to 

 two principal points ; 1st, which of the two sorts of gold, whether 

 that which is very ductile, or that which is as hard as is compatible 

 with the process of coining, suffers the greatest loss under the gene- 

 ral circumstances of friction ; and 2dly, 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. With a view of arriving at some certain data respecting 

 these questions, three objects were principally kept in view, which 

 gave rise to the three sections that compose the body of the paper. 

 The first of these comprehends the chemical experiments, those which 

 relate to the effects produced upon gold by the addition of different 

 metals in certain relative proportions ; the second includes those 

 experiments which relate to the different degrees of density observed 

 in gold when differently alloyed ; and the third consists of those 

 experiments which may be called mechanical, and which were ex- 

 pressly intended to ascertain the comparative wear of different kinds 

 of gold by various modes of friction. 



In the numerous set of experiments which are described in the first 

 section, the effects of every metal and semi-metal upon the colour 

 and ductility of gold were ascertained with all possible care and pre- 

 cision. All the semi-metals were found to affect the quality of gold 

 too essentially, though in different degrees, to be ever used as alloys. 

 And among the metals, lead in very small proportions was likewise 

 found to render gold so completely brittle, as to be absolutely unfit 

 * coinage. Tin was not near so pernicious ; and iron, though it 



