26 THE ELEMENTS.
reaction by heating. Use 1 g. of sodium in all. After cooling,
break the test tube and collect the amalgam, which will keep
indefinitely when preserved in well-stoppered vessels. A lump
of sodium amalgam placed in water gives a uniform evolution of
hydrogen.
Ammonium Amalgam. Introduce a few grams of sodium
amalgam into 20 to 30 c.c. of ice-cold, concentrated ammonium
chloride solution; the amalgam at once begins to swell, and is
changed to a gray spongy mass of extremely voluminous ammo-
nium amalgam. Ammonium amalgam decomposes completely,
within a short time, into hydrogen, ammonia, and mercury.ROASTING PROCESSES.
- Lead from Galena.
By the "roasting process" galena is first partly oxidized at a relatively
low temperature to lead oxide or lead sulphate; then without any intro-
duction of air the mass is heated more strongly, whereby the oxygen of the
lead oxide and lead sulphate accomplishes the oxidation of all the sulphur
present to sulphur dioxide. Only those ores are suitable for roasting which
contain but small amounts of silicates and of sulphides of other metals.
Silicates are harmful, since they give rise to the formation of lead silicate.
As it is difficult to conduct the partial roasting satisfactorily upon a small
scale, it is better in the following experiment to start with a mixture of galena
and litharge:
PbS + 2 PbO = 3 Pb + SO 2 ,
PbS + PbSO 4 = 2 Pb + 2 SO 2.
Place an intimate mixture of 20 g. very finely-powdered and
sifted galena and 37 g. litharge in a small clay crucible, and heat
it in a furnace as quickly as possible to a bright red heat. After
about half an hour, allow the contents of the crucible to cool, and
hammer away the regulus of metallic lead from the broken crucible
to which it adheres because of a glassy film of lead silicate. To
purify the lead, melt it together with some borax in a porcelain
crucible. Calculate the yield in per cent of the theoretical.
CUPELLATION.
- Pure Silver from Coin Metal.
If an alloy of impure precious metal, such as gold, silver or platinum, is
melted on a cupel in an oxidizing atmosphere, the lead and other base metals
present are oxidized and are absorbed by the porous material of which the