cupel, together with the copper and other oxidisable metals 

 present, and the silver and gold remain behind in the form of a 

 button (D), which may also contain platinum, indium, or other 

 metals possessing similar properties. 



3rd Process. These buttons are hammered out into discs (E)< 

 which, after being annealed, are rolled into thin strips (F), and 

 these are again annealed and bent into loose coils or " cornets " 

 (G). The annealing takes place in an iron tray. 



4th Process. The cornets are placed in small perforated cups 

 of platinum arranged in a perforated tray of the same metal. 

 The whole is then introduced into a platinum boiler, which 

 contains boiling nitric acid of specific gravity 1/26, in which it 

 is allowed to remain for 15 minutes; it is then transferred to a 

 similar boiler with acid of specific gravity 1-31. The silver is 

 removed by the action of the acid, and the gold remains in a 

 spongy state (H). 



5th Process. The gold sponge (which retains the original 

 form of the cornet) is rendered coherent by annealing at a dull 

 red heat. This is accomplished by introducing the platinum 

 tray into the muffle. The cornets then assume the appearance 

 of (I). 



6th Process. The final operation consists in weighing the 

 cornets. This is done in a specially constructed " assay " balance, 

 which is capable of indicating about .^^th of a grain when 

 loaded with 7'5 grains in each pan. The weights employed bear 

 a decimal relation to the original weight of the piece of metal 

 operated upon. The percentage of gold, therefore, present in the 

 alloy, is at once indicated without calculation. The weighing 

 in the first process was of course conducted on the same or a 

 similar balance. 



6. Appliances used in the assay of silver. 



1. Pipette for " standard " salt solution used in silver 

 assaying. 



2. Pipette for " decimal " salt solution. 



1876. Lent ly the Master of the Mint. 



The assay of silver can be conducted by cupellation, an 

 operation similar to that already described in the second process 

 of the assay of gold, the only differences being that no pure 

 silver is added to the assay piece, and the operation terminates 

 when the button (D) has been obtained and weighed. The wet 

 method of Gay Lussac is, however, now usually employed for the 

 assay of silver when the " standard " is approximately known, 

 and the alloy contains not less than 50 per cent, of silver. It 

 consists in precipitating the precious metal from the solutions of 

 a known weight of the alloy to be assayed, the weight being so 

 adjusted that sufficient silver is present to neutralise a given 

 volume of the solution employed as a precipitant. This solution 

 is usually one of common salt, but hydrochloric acid or hydro- 



