of pyrites, if no nitre were added, 110 grams of lead would be
got; or, if there was not sufficient oxide of lead to yield this
quantity of metal, the button would be sulphury. To reduce the weight of
the button by 80 grammes, we should add 20 grams of nitre, if litharge
were used; or if red lead were used, we should add 16 grams of nitre,
_since the oxidizing effect of 20 grams of red lead is equivalent to
that of 1 of nitre_, and since 80 grams of red lead are generally used
in a charge. Two assays of an ore of this kind with these quantities of
nitre gave 26.0 grams of lead with litharge, and 22.5 grams with red
lead.
It is best to use in these assays 80 grams of red lead, 20 of soda, and
5 of borax, with 20 grams of the ore. If the lead got by the preliminary
fusion in a small crucible with litharge (described under "_ores
containing much sulphides_") is known, the following table will indicate
the quantity of nitre, or flour, to be added with this charge:--
-------------------------------+-------------------+------------------
Lead got in Preliminary Fusion | Flour to be added | Nitre to be added
with 3 grams of Ore. | to the Assay. | to the Assay.
-------------------------------+-------------------+------------------
0.0 gram | 3.3 grams | none
3.
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