Parting in Metallurgy, is an operation by which gold and silver are separated from each other. In this sense it is the same with refining metals, or obtaining them in a pure state. Gold and silver are called perfect metals, because they are capable of withstanding the action of very strong heat. All other metals are reduced to the state of oxides when subject to fire with access of air. Gold and silver may, therefore, be purified from baser metals by keeping them melted till the alloy be destroyed; but this process is tedious and expensive, from the great consumption of fuel. A shorter and more advantageous method of refining gold and silver has been discovered. A certain quantity of lead is put into the crucible with the alloy of gold and silver, the whole is exposed to the action of the fire; and the lead being quickly converted by heat into an oxide, which is easily melted into a semi-vitrified and powerful vitrifying matter, called litharge, we have only to increase the proportion of imperfect metals; and, by uniting with these imperfect metals, it communicates to them its property of being very easily oxidated.
By its vitrifying and fusing property, exercised with force upon the calcined and naturally refractory parts of the other metals, it accelerates the fusion, scorification, and separation of these metals. In this operation the lead is scorified, and scorifies along with it the imperfect metals. It separates from the metallic mass, floats upon the surface of the melted mass, and becomes vitrified; but as the litharge would soon cover the melted metal, and, by preventing the access of air, prevent the oxidation of the remaining imperfect metals, such vessels are employed as are capable of imbibing and absorbing in their pores the melted litharge, and thus removing it out of the way; or, for large quantities, vessels are so constructed that the fused litharge, besides being soaked in, may also drain off through a channel made in the corner of the vessel. Vessels made of lixiviated wood, or bone ashes, are most proper for this purpose. These vessels are called cupels, the process itself cupel-lation. The cupels are flat and shallow. The furnace should be vaulted that the heat may be reverberated upon the surface of the metal during the operation. A crust or dark-coloured pellicle is continually forming upon the surface.
When all the imperfect metal is destroyed, and the scorification has ceased, the surface of the perfect metal is seen clean and brilliant, forming a kind of ful-geration called lightning. By this mark the metal is known to be refined.