410 On Cupellation with the Blowpipe. 
When the cupellation is performed on mica, the oxydation is 
nearly as rapid as on the bone ash cupel, and the globule is kept 
partially immersed in the melted oxyd of lead, and thus the silver 
that would otherwise be lost in the litharge, is mostly taken up 
by the lead.* A little skill in the operator will enable him when 
the oxyd has accumulated to some extent around the globule of 
lead, to slide the melted globule by a slight inclination to another 
place, without losing it off from the mica. This obviates in a 
great degree the loss of time, that would otherwise arise from 
the necessity of cooling to detach the globule, put it in anew 
lace and heat it again to the proper temperature. When the 
cupellation globule is reduced to the size of a mustard seed, 
whether bone ash or mica be used for cupelling, it is well to re 
move it to a new very smooth cupel, or to a fresh piece of good 
mica, and then, when melted, make the globule slide by inclining 
the cupel, and by means of the blast, to fresh surfaces, until, final- 
ly, the globule of silver or gold remains pure, or as nearly so as 
cupellation will make it. No silver is lost in this way, except 
the extremely minute quantity carried off in the litharge, and that 
which is vaporized if the heat be too high. 
The method of cupellation on mica I consider more accurate 
than that on bone earth, and if the mica be of good quality, s0 
as not to exfoliate at all by heat, or permit the litharge at the 
Pee 
s in 
weight may be seen on its surface by the naked eye. When 
_* This is the explanation of the well known fact that the eupellation of lead in 
the large way, always gives a larger yield of silver, than is indicated by cupellation 
. 
in the small way on bone ash cupels. 
