Table of Contents
Usual Charge
Mix 10 grams of the pulped ore with 40 grams of pulverized potassium cyanide.
Melting
Put the charge into a 20 gram crucible or one of equivalent capacity, and cover the top of the charge with about 10 grams of dry table salt. The salt cover prevents the charge from boiling over the top of the crucible. The reduction should be made in twenty minutes in the melting chamber of a gasoline furnace. When the reduction is complete, which may be known by the quiescent state and the fluidity of the charge, remove the crucible from the furnace and cover with a crucible cover.
Recovering the Button
When it is cold break the crucible to recover the button. Be careful in breaking the crucible as the button will be very brittle.
To separate foreign metals, break up the button into fine particles and add chemically pure nitric acid, which converts the antimony to antimonic acid which is insoluble. Filter, wash, dry and ignite in a porcelain crucible.
Estimating Results
Antimonic acid is 79 per cent metallic antimony; therefore multiply the weight found by .79, which will give the amount of metallic antimony. Where a small filter is used the weight of the ash may be ignored. The ignition consists in drying the filter containing the antimonic acid and in heating it red hot. See that the filter is reduced to a white ash and is not simply carbonized. This may be done in a porcelain crucible (see Fig. 26), in the muffle or in the flame of a Bunsen burner.