Page:Proceedings of the Royal Society of London Vol 1.djvu/125

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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. Hatchetthas been pleased to communicate 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 general 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 include 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 precision. 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 for coinage. Tin was not near so pernicious; and iron, though it