Hoke:Refining-Page-106

From GoldRefiningWiki
Jump to: navigation, search
Page 106
Previous page Index Next page


regia, but that platinum reacted so slowly that he heated the dish
to hasten matters. This difference in speed with which gold and
platinum are attacked by cold aqua regia is important and will be
referred to again later.
 There is another respect in which platinum differs from gold.
You will recall from Chapter VI (See Quartation) that gold can be
separated from silver by treating a silver-rich alloy with nitric or
sulphuric acid. That is, if an alloy containing three times as much
silver as gold is boiled with either of these acids, the silver will
dissolve and all the gold will remain as a brown powder, thus
effecting a separation. This method cannot be used to separate
platinum from silver, as platinum-silver alloys behave quite differently
from gold-silver alloys. Thus, if you should expose an
alloy of 95% silver and 5% platinum to boiling nitric acid, everything
will dissolve, the platinum forming a soluble platinum nitrate,
from which it is not easy to recover the platinum. If you should
expose an alloy of 75% silver and 25% platinum to nitric acid, most
of the silver and some of the platinum will dissolve, and there will
be a considerable residue which contains both metals. In other
words, you will not effect a separation.
 Silver-rich platinum alloys react to boiling concentrated sulphuric
acid in about the same way-no separation is effected. With sulphuric
acid that is slightly diluted, a fair separation can be obtained.
This point will be mentioned again in the latter part of Chapter XII.

 Before the reader becomes an accomplished refiner he will come
to know several other characteristics of platinum, but for the
moment (since we are anxious to begin actual work) we shall
content ourselves with only one or two further observations.

 (Several new chemicals and pieces of equipment will be needed in
Chapters XI, XI1 and XIII. These are described in Chapter XI. Of
these, the following will be employed now: the porcelain crucible and
the clay triangle that supports it; sodium chlorate; ammonium chloride.)

                PLATINUM AND AMMONIUM CHLORIDE

 Place in a small beaker a half ounce or less of the platinum solution
you prepared in Chapter IX. This is a solution of platinum in
hot aqua regia, made up with as little aqua regia as would do the
work, plus water; its chemical name is "Platinum Chloride" or
"Chloro-platinic acid." Notice the yellow color. In a second vessel


Page 106
Previous page Index Next page
Personal tools
Google AdSense