ASSAY OF GOLD AND SILVER COINS. 423 



brought to the same temperature, the leaden ball, with its contents, is put into 

 one of the cupels, the furnace cK)se(l, and the oj)eration allowed to proceed until 

 all agitation is ceased to bo observed in the melted metal and its surface has 

 become bright. 



This is an indication that tlio whole of the base metals have been converted 

 into oxides and absorbed by the cuj)el. 



The cupellation being thus finished, the metal is allowed to cool slowly, ai*l 

 the disk or huttun which rt forms is detached from the cupel. 



The button is then flattened by a hammer ; is annealed by bringing it to a 

 red heat; is laminated by passing it between rollers; is again annealed; and is 

 rolled loosely into a spual or coil called a cornet. It is now ready for the pro- 

 cess of quartation. 



For this pnq)Ose, it is introduced into a matrass containing about \^ ounces 

 of nitric acid at 22° of Baume's hydrometer, and in this acid it is boiled for 1 

 minutes, as indicated by a sand-glass. 



The acid is then poured off, and three-fourths of an ounce of stronger acid, at 

 32°, is substituted for it, in which the gold is boiled for 10 minutes. 



This second acid is then also poured off, and another equal charge of acid of 

 the same strength is introduced, in which the gold is kept for 10 minutes longer. 



It is then presumed that the whole of the silver has been removed, and the 

 gold is taken out, washed in pure water, and exposed, in a crucible, to a red 

 heat, for the purpose of drying, strengthening, and annealing it. 



Lastly, the cornet of fine gold thus formed is placed in the assay balance, and 

 the number of thousandths which it weighs expresses the fineness of the gold 

 assayed, in thousandths. 



TEST ASSAY. 



To test the accurac}^ of this process, the following method is emplo^'cd : 

 A roll of gold, of absolute purity, which has been kept under the seal of the 

 chairman of the assay commissioners, is opened in their presence, and from it is 

 taken the weight of 900 parts. To this are added 75 of copper and 25 of silver, 

 so as to form, with the gold, a weight of 1000 parts of the exact legal standard. 

 This is passed through the same process of assay as the other gold, and at 

 the same time. After the assay is finished, it is evident that the pure gold re- 

 maining ought to weigh exactly 900. If, however, from any cause, it be found 

 to difi'er from this weight, and therefore to require a correction, it is assumed 

 that the same correction must be made in the other assays, and this is done ac- 

 cordingly. 



ASSAY OF SILVER COINS. 



PRINCIPLES OF TUB OPERATION. 



The standard silver of the United States is so constituted that of 1000 partj 

 by weight 900 shall be of pure silver, and 100 of copper. 



The process of assay requires that the exact ])rop(»rtion of silver in a given 

 weight of the compound be ascertained, and this is done by a method called the 

 liamkl assay, wliich may be exj)lained as follows: 



The silver and co})i)er may both be entirely dissolved in nitric acid ; and if to 

 a solution thus made another of common salt in water be added, the silver will 

 be precii)itated in the form of a white p(jwder, which is an ins^duble chhjrido, 

 while the copper will remain unatl'ected. 



Now it has been ascertained that 100 jiarts by weight of pure salt will con- 



