107 



and pressure. In the second, 200 pieces of gold differently alloyed were 

 inclosed within a wooden box, which was kept constantly turning 

 round, until, by the continued rubbing and striking of the pieces 

 against each other, and against the sides of the box, they were found to 

 be perceptibly diminished. And in the third mode, the pieces to 

 be examined were pressed against the rim of a flat horizontal wheel, by 

 means of equal weights, so that by turning the wheel round, they all 

 suffered an equal degree of friction. The part of the wheel against 

 which the pieces rubbed was sprinkled or coated with some kind of 

 powder, which was varied in the different experiments. 



The general results of the many experiments made with this appa- 

 ratus were, 1. That when equal friction, assisted by a moderate pres- 

 sure, takes place between pieces of coin which are in each series of 

 a similar quality, then, abrasion is most commonly produced in an 

 inverse ratio to the degree of ductility ; 2. That the contrary effect 

 happens when pieces of different qualities rub against each other, 

 the more ductile metal being then worn by that which is harder ; 

 and 3. That earthy powders and metallic filings produce similar ef- 

 fects, and tend to wear the different kinds of gold in proportion to 

 their respective degrees of ductility. 



The practical inferences to be deduced from these results are, 

 that pure gold, being extremely ductile, is not the most proper to be 

 formed into coin ; that gold, on the other hand, brought by its alloy, 

 to the greatest degree of hardness that will bear the manipulation of 

 coining, will be so destructive to the instruments in the Mint, as to 

 render the expense occasioned by this detriment much greater than 

 the small saving that would accrue from the greater durability of the 

 metal ; and that hence gold of a moderate ductility must be that 

 which is best adapted for coin, which degree of ductility will be 

 found in the standard proportion of one-twelfth of alloy consisting of 

 about equal parts of silver and copper. 



Several incidental circumstances are mentioned at the close of this 

 paper, some of which relate to the cause of the changes of colour in 

 gold coins, which are ascribed to certain chemical changes in the 

 alloy near the surface of the piece during the processes of annealing 

 and blanching. We are also informed that the obliteration of the 

 impressions on gold coins is not always attended with a diminution 

 of weight, but that the supposed abrasion of the prominent parts is 

 in fact a depression of those parts into the mass, bringing them to a 

 level with the rest. 



Upon the whole, our author concludes that the great loss which 

 the gold coin of this kingdom is stated to have sustained, cannot 

 possibly be attributed to any important defect in the composition or 

 quality of the standard gold ; and that all that can be said upon this 

 subject is, that some portion of this loss may have been caused by 

 the rough impression and milled edge now in use, by which each 

 piece of coin acts and is acted upon by the others, in the manner of 

 a file or rasp. 



