J4.g EXPERIMENTS ON VARIOUS ALLOYS OK GOLD. 



The machine was then put in motion, until the index (howed 

 that 2S6690 revolutions had been performed ; and, as a double 

 crank aded during each revolution, the pieces were rubbed 

 againft each other alternately, in oppofite diredions, 573380 

 times, being twice the number of the revolutions. 



The twelve pieces of ftandard gold, being taken out, were 

 ■ weighed, and were found to have loft 8,60 grs. 



Experiment II. 

 Of gold alloyed Twelve pieces of gold combined with an equal proportion 

 with an unequalof copper, and without any impreffion, loft 103,11 grs. in 

 weight of copper. ^, , . 



^ ^^ 70S40 revolutions. 



Experiment III. 



Of finecopper. Twelve firailar pieces of fine copper, loft 174,80 grs in 

 22200 revolutions. 



Hence it appears, that ftandard gold lofes lefs by fridion 

 than gold much debafed by copper, and this lefs than copper 

 alone. 

 Gold alloyed The next feries of experiments was made with gold dif- 



with copper, ferently alloyed ; when gold 1. made ftandard by copper, 2. 

 JronY' ""' ^" reduced to 18 carats by copper, 3. made ftandard by copper 

 andfilver, 4. made ftandard by filver, 5. of 23 car. 31 grs. fine, 

 6. made ftandard by tin and copper, 7. made ftandard by iron 

 and copper, 8. alloyed with an equal quantity of copper, was 

 found to have loft in the following proportions, in the order 

 in which they have been enumerated. Ogrs. Ogrs. 0,10 grs. 

 0,10grs. 4,20 grs. 15,30grs. 21,60 grs. 65,78grs. The wear of 

 the pieces alloyed with equal parts of gold and copper, and 

 with iron and copper, was fo rapid, that they were obliged 

 to be taken out of the machine after 105480 revolutions ; and 

 thofe containing tin were worn fo thin in 189000 revolutions, 

 as to require being removed : the reft fuftained 200300 re- 

 volutions, whence their comparative lofs was ftill lefs than 

 as above given. 

 Gold fimilarly This experiment being made on fmooth, flat pieces, it was 

 alloyed and repeated with others of fimilar compofition ftamped with the 

 die before defcribed, only omitting the compound of equal 

 parts of gold and copper, and adding pieces of ftandard 

 lilver and of fine copper. The number of revolutions were 

 only 20680, and the pieces, taking them in the order already 

 mentioned, now loft refpe<aively : 0,60 grs. 4,80 grs. 1,20 grs, 



3,5a 



