SILVER COINS. 397 



f\c gravity ascertained. The specific gravity of silver varies, Specific gra- 

 as is well known, according to circumstances. I melted two g^i^ej, 

 ounces of- pure silver, and let it cool in the bottom of a black- 

 lead crucible previously heated. Its specific gravity was 

 10.3946. The same mass was fused a second time, and cast 

 into a thin plate. Its specific gravity was now reduced to 

 10.1790. When this jjlate had been passed between rollers, its 

 specific gravity was found to be 10.4812. By hammering the 

 round button, its specific gravity became 10.4 177. 



The coin afler being cleaned was put into a matrass with a Solution of the 



m ■ • r ... . 1 ,-1 1-1- coin in nitric 



sufficient quantity of pure nitric acid previously diluted with jj^,;^ diluted. 



about twice its bulk of water. The solation as soon as the 

 acid ceased to act was poured off, and the black powder which 

 usually remained, was repeatedly digested on a sand bath with 

 small quantities of nitric acid. It was then washed with dis- 

 tilled water, and dissolved in nitromuriatic acid. - The '^^^""*^'f°'^'" 

 1 • 1 ■ , 1- • 1 T . /. • 11 ed gold dissolv- 



soJution was mixed with liquid sulphate of iron, and the ed in nitro- 



blackibh powder which fell was washed, and formed into a "Hinatic acid 



,. , . , , . . . , , and precipitat- 



sohd mass, sometimes by amalgamating it with mercury, and ed, &c. 



driving off the volatile metal by heating the amalgam in a 

 small porcelain crucible ; sometimes by forming it into a ball 

 with calcined borax and fusing it into a button before the 

 blow. pipe. The metals thus obtained was the gold. It never ex- 

 ceeded 2^^o"th part of the coin, and seldom amounted to to'd-o^^^i 

 part. In some coins, no gold whatever could be detected. 

 In some of the following analysis, the black powder which re- 

 mained when the coin was first dissolved in nitric acid, was 

 melted into a button, and weighed. This button was then 

 treated with nitromuriatic acid : if it dissolved completely, it 

 was considered as pure gold ; but if it left any residue of muri- 

 ate of silver, this muriate was carefully dried and weighed, 

 and the proportion of silver thus indicated was subtracted from 

 the weight of the button ; the remainder was considered as 

 the weight of the gold contained in the coin. 



3. The nitric acid solution was mixed with a solution of The nitric sola- 

 common salt, more than suf^cient to separate the whole of the te*d bv'^com^^' 

 silver. The muriate of silver was allowed to settle at the salt and the 

 bottom of the vessel, and the liquid carefully decanted off. ^"'ijet-hed!' 

 Distilled water was poured upon the precipitate, the mixture 

 was well stirred with a glass rod, and left at rest till the mu- 

 riate was deposited ; then the water was decanted off, and a 



new 



