152 



■pniJtion of gold 

 by whiting, 

 fand, filings of 

 ftandard gold, 

 and of iron. 



General refults. 



Fine gold lofes 

 its imprefiion. 



Very hard gold, 

 improper for 

 coin ; Why. 



EXPERIMENTS ON VARIOUS ALLOYS OF GOLD. 



The pieces were properly fixed in their refpeftive fockets 

 and frames, and were placed fo as to bear upon the table, 

 with or without additional weights. 



The table was moved by a wheel and pinion, fo calculated 

 as to avoid too rapid a motion ; and the revolutions were de- 

 noted, as in the former experiments, by means of a counter. 



The table was covered with fine powdered whiting, with 

 fine white writing fand, with filings of gold made ftandard by 

 copper, and laftly filings of iron. The laft three were fi,xed 

 on the table by means of a folution of ifinglafs. Gold of dif- 

 ferent kinds as before, flandard ftlver, and fine copper, both 

 fiamped and unftamped, were fubjeded to the different 

 trials. 



From the whole of the preceding experiments, made with 

 the three different machines, viewed and compared together, 

 the author infers, 



I ft. That when equal fri6tion, aflilled by a moderate pref- 

 fure, takes place between pieces of coin of a fimilar quality, 

 abrafion is moft commonly produced in an inverfe ratio to the 

 ductility. 



2d. That the contrary effe6t happens, when pieces of dif- 

 ferent qualities rub againft each other ; for then, the more duc- 

 tile metal is worn by that which is harder.* 



Sd. That earthy powders and metallic filings produce 

 fimilar effefts, and tend to wear the different kinds of gold 

 in proportion to their refpe6live degrees of du6lility. 



Fine gold, being extremely foft and dud^ile, fuftains a con- 

 fiderable lofs, under many of the general circumflances of 

 fri6lion ; and as at all times it appears certain, that the im- 

 preflions which have been ftamped upon it are moft eafily 

 obliterated, even when actual abrafion does not take place, 

 there is much reafon to conclude, that gold of fuch extreme 

 duftility is not that which is the moft proper to be formed 

 into coin. 



But gold of the oppofile quality, or at leaft fo hard as to 

 be jnft capable of being rolled and ftamped, feems to be 

 equally improper for the purpofe of coin. For, even fup- 



* Some experiments made at Paris, in 1790, upon pure and upon 

 alloyed filver are concifely mentioned, the refults of which appear 

 to be nearly the fame as thofe of the prefent experiments upon gold. 



pofing 



