Using 80 grams of red lead and wanting a button of 20 grams, we should
add 3.3 grams of flour.
80/5 = 16; 16+20 = 36; 36/11 = 3.3 nearly.
The following are some results obtained which will illustrate the
rule:--
Red Lead used. Flour used. Lead got.
40 grams 3 grams 25.0 grams
100 " 3 " 13.5 "
80 " 4 " 30.0 "
80 " 5 " 40.0 "
_On the Reducing Effect of Metallic Sulphides, and the Counteracting
Effect of Nitre._--The sulphides found in ores will reduce a button of
lead from oxide of lead just as flour does; and, as charcoal, flour and
tartar differ in their reducing power, so equal weights of the different
mineral sulphides throw down different weights of lead.
One gram of iron pyrites yields about 11 grams of lead. One gram of
copper pyrites, blende, fahlerz, or mispickel, yields 7 or 8 grams of
lead, whilst 1 gram of antimonite will give 6, and 1 gram of galena only
a little over 3 grams. It is evident that if an ore carries much of
these sulphides, the quantity of lead reduced will be very much larger
than that required for an assay. To counteract this effect nitre is
added; _1 gram is added for each 4 grams of lead in excess of that
required_. For example: with a 20-gram charge of an ore containing 50
per cent.
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