322 Oil Cupellation. 



about two years with perfect success, and I have no hesitation in 

 recommending it to the pubhc. As it is a matter of public inter- 

 est to simpUfy all such operations, I have thought it proper to send 

 you a description of my method of cupellation. 



If the ore to be examined for silver or gold, be a lead ore, it is 

 to be reduced to the metallic state by the ordinary methods. A 

 small piece of the lead, of the size of a duck shot or larger, is to 

 placed on a thin slip of mica, and then melted by the blowpipe 

 flame of a candle or lamp. As the heat increases above the melt- 

 ing temperature of the lead, the globule will become perfectly 

 brilliant, and finally a peculiar flickering, brilliant surface will 

 shew itself, caused by the oxidation of the metal and the fusion 

 of the oxide of lead. The oxide of lead melts at the temperature 

 at which this appearance is developed, and spreads itself on the 

 mica. It soon ceases to spread, and collects around the globule 

 of melted lead, which is continually diminshing in magnitude, 

 in consequence of the oxidation of the metal in the oxidizing 

 blowpipe flame. When the globule of melted lead is nearly bu- 

 ried in the mass of the surrounding oxide, the slip of mica should 

 be permitted to cool. The globule of lead should then be re- 

 moved by forceps, or other means, to another place on the slip of 

 mica, where the same oxidizing process is to be repeated succes- 

 sively. Finally, when the globule shall have been reduced to 

 the size of a small grain of sand, it should be placed on a fresh, 

 clean slip of mica, and again heated in the same manner. If the 

 lead contains the least trace of silver, it is easily made manifest 

 in this way, because, the silver when once free of lead, (which 

 continues to oxidize to the last, ) remains unchanged, as a brilliant 

 white globule, which can be frequently seen distinctly with the 

 naked eye, and when too small for this, by examination with the 

 magnifier. If the oxidation of one globule of the lead does not 

 give decisive indications of silver, a satisfactory conclusion as to 

 the lead being argentiferous or not, may be obtained by oxidizing 

 five to ten such globules down to a very small size, and then 

 uniting these by fusion on a slip of mica, and continuing the ox- 

 idation to its ultimate limit. A person accustomed to blowpipe 

 manipulation, can determine in a few minutes, if silver be present 

 in any lead which may be suspected to contain it. With the ta- 

 ble blowpipe, or the hydrostatic blowpipe, an ounce of lead may 

 be cupelled in a very short time, and the relative quantity of sil- 

 ver determined, if it be appreciable. 



