EXPERIMENTS ON VARIOUS ALLOYS OF GOLD. 159 



■metals, and does not appear to have been noticed. This is long 

 continued fridtion, which always produced a diminution in the 

 fpecific gravity of the pieces of metal expofed to it. 



Among the other leCs powerful caufes which produce fome Rolling iacreafes 

 alteration in the fpecific gravity of gold, the procefles of rolling, "' 

 and of annealing, may alfo be enumerated; for, in the courfe Annealing di- 

 of thefe experiments it appeared that the fpecific gravity of ™'"' ^* ''* 

 the bars, &c. was in a fmall degree increafed by rolling, and 

 that the contrary effect was produced by annealing. 



The fpecific gravity of gold, 23 car. 3| grs. fine, when rolled 

 and iiamped without being annealed, was found to be 19,277 ; 

 but, when the fame was annealed, the fpecific gravity was 

 19,231, after fiamping. 



Mr. H. is how^ever, inclined to believe, that annealing had re- 

 duced the fpecific gravity to much lefs than is here flated ; and 

 that the fubfequent operation of ftamping had, in fome meafure, 

 compenfated the eflfeds of annealing. For, in the experiments 

 lately mentioned, it was proved, that the fpecific gravity of 

 the pieces which had not been annealed, was reduced, by long 

 continued fri6tion, from 19,277 to 19,171 ; an effedl furpading 

 that which refulted from annealing by ,060 (19,231-19,171 

 =,060 ;) and, if heat was the caufe, the reverfe might have 

 been expected, inafmuch as the annealing heat exceeded that 

 which was produced by fridion ; but, as this was not the cafe, 

 he is induced to be of opinion, that the fpecific gravity was 

 again increafed, by the fubfequent fiamping of the annealed 

 pieces. 



In addition, therefore, to thofe caufes of variation in fpecific 9^"('^* of varia- 

 gravity which are the immediate confequences of hydroftatical gravity enu- 

 operations, fuch as, the dilFerent height of the column of water, merated. 

 and the changes of temperature to which it Is expofed during 

 .the experiments, the following, as far as they concern metal- 

 lic fubfiances, n:iay be enumerated. 



1. Imperfedions in the interior of the mafs, which are pro- 

 duced during the proceffes of melting and catling. 



2. The difference of denfily in parts of the fame mafs, re- 

 fulting from the quality and quantity of the metal, from the 

 nature of the mould, from the more or lefs vertical pofition of 

 it, and from the height of the column or bar of metal which 

 is cafl. 



3. The 



