Assaying Agents Flashcards
o Very strong basic flux
o Yellow to orange color
o Melting point: 8830C
o Aids in fusion of basic flux; furnishes the Pb that collects the Au and Ag when reduced; also acts as an oxidizing and desulfurizing agent
Litharge
o Powerful basic flux
o Melting point: 8520C
o Combines with silica and alumina, producing fusible silicates and aluminates (slag)
Sodium Carbonate
o Alternative to sodium carbonate; only that it is very expensive
Potassium Carbonate
o These are active and readily fusible acid flux
o White colored; melting point: 7420C
o Used as cover to prevent loss of ore which usually results from the escape of gas as the temperature is brought below that of incipient fusion
Borax Glass
o A strong acid flux
o Melting point: 17550C
o Combines with metal oxides to produce the slag, which in many cases are considerably more fusible that SiO2 itself
Silica
o Powerful reducing agent
o Reduces litharge (PbO) to Pb for the collection of Au and Ag
o If ore contains ferric oxide, MnO, and some easily reduced oxide, more flour is added
Flour
o Powerful oxidizing agent
o Melting point: 3390C
o Oxidizes sulfides, arsenides, and antimonides
o It is used to control the size of the Pb button when the reducing effect is very high
Potassium Nitrate
o A crude bitartrate of potassium obtained from the wine barrels
o A reducing agent and a basic flux
o One of the best reducing agents
Argols
o Used as a reducing agent in the copper assay
o A refined bitartrate of potassium
o Like argols, it reacts on heating to produce K2O
Cream of Tartar
o A desulfurizing and reducing agent
o When combined with the litharge, it reduces the litharge to form the oxide of iron, thus acting as a basic flux
Iron
o A powerful reducing and desulfurizing agent
o Combines with oxygen to form potassium cyanate and with sulfur to form sulphocyanides
Potassium Cyanide
o Used as cover to exclude the air and to wash the sides of the crucible and to prevent small particles of lead from adhering thereto
o Does not enter the slag, but floats on top of it
Salt
o When melted, it is very fluid and assists in liquefying the charge, although it is inert and does not enter into chemical combinations with the other charge constituents
Fluorspar
o A powerful flux commonly used in the manufacture of enamels and the melting of bullion
o Has the property of dissolving alumina
o Increases the coefficient of expansion of the slag
Cryolite
