REFINING METALS. 217 



corruscation, called lightning. By this mark the 

 metal is known to be refined. 



Purification of gold by antimony. 



When gold contains only a small quantity of alloy, 

 it may be separated from them by melting it in a 

 crucible that will hold twice its quantity at least, and 

 throwing upon it, whilst in fusion, twice its weight 

 of crude antimony (sulphuret of antimony). The 

 crucible is then to be covered, and the whole is to 

 be kept in a melting state for some minutes ; and 

 when .the surface sparkles, it is quickly to be 

 poured into an inverted cone, which has been pre- 

 viously heated and greased. By striking the cone 

 on the ground, the metal will come out when cold. 

 The compact mass consists of two substances ; the 

 upper part is the sulphur of the crude antimony, 

 united with the impure alloy ; and the lower part 

 is the gold, united to some of the regulus of anti- 

 mony, proportionable to the quantities of metals 

 which have been separated from the gold, which 

 are now united with the sulphur of the antimony. 

 This regulus of gold may be separated from the 

 regulus of antimony by simple exposure to less 

 heat than will melt the gold, because antimony is 

 volatile in such a heat, and is then dissipated. If 

 the gold is not sufficiently purified by this first pro- 

 cess (which is often the case,) it must be repeated 

 a second, and even a third time. When a part is 

 dissipated, more heat is required to keep the gold 

 in fusion ; therefore, the fire must be increased to- 

 wards the end of the operation. The purification 

 is completed by means of a little nitre thrown into 

 the crucible, which effectually calcines the remain- 

 ing regulus of antimony. Sometimes, after these 



