322 On Cupellation. 
about two years with perfect success, and I have no hesitation in 
recommending it to the public. As it is a matter of public inter- 
est to simplify 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~ 
ively. 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 cuipelled ‘in a very short time, and the relative s apr of sil- 
_ Ver determined, if it be appreciable. 
