Using the gold salt in this way, the principal difficulty experienced in
holding gold wire unflinchingly in the exact position vanishes, while
only a comparatively low temperature and small amount of gold is
necessary. Care must be taken to withdraw the platinum from the flame
just at the moment the gold is seen to run, for if the heat be continued
longer, the gold alloys with a larger surface of platinum, spreads, and
leaves the aperture empty. As in the case of all gold-soldered vessels,
the article cannot afterward be safely exposed to a temperature higher
than that at which the soldering was effected, and on this account it is
advisable to use as small an amount of auric chloride as possible. When
the perforations are of comparatively large size, the repairing is not so
easy, owing to the auric chloride, on fusing, refusing to fill them. I
find, however, that if some spongy platinum be mixed with a few
milligrammes of the gold salt, pressed into the perforation, and heat
applied as directed, a very good soldering can be effected. It is well to
hammer the surface of the platinum while hot, so as to secure perfect
union and welding of the two surfaces. This may be done in a few minutes
in such a manner as to render the repair indistinguishable. Strips of
platinum may be joined together in much the same way as already
described--a few crystals of auric chloride placed on each clean surface
and gently heated till nearly black, then bound together and further
heated for a few moments in the blowpipe flame. Rings and tubes can also
be formed on a mandrel, and soldered in the same fashion, and the chemist
thus enabled to build up small pieces of apparatus from sheet platinum in
the laboratory.--_Chem. News._

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