has been described under the head of
shellac attachments. It does not very much matter whether both ends
are coppered before one is soldered up or not. At the conclusion of
the whole process the superfluous copper and silver are dissolved off
by a little hot strong nitric acid applied on a glass hair pencil.
This is best done by holding the thread horizontally with the
assistance of clip stands.

If the thread is too delicate to bear brushing, the nitric acid may be
applied by pouring out a big drop into a bit of platinum foil and
holding this below the thread so as to touch it lightly. The
dissolving of the copper and silver is, of course, followed by copious
washing with hot water. This process is more laborious than might be
imagined, but it may be shortened by heating the platinum foil
supporting the water (Fig. 74).

Fig. 74

The washing part of the process is, in the opinion of the writer, the
most difficult part of the whole business, and it requires to be very
thorough, or the thread will end by drawing out of the solder. In
many cases it is better to try to do without any application of nitric
acid at all, but, of course, this involves silvering and coppering to
exact distances from the ends of the thread--at all events, in
apparatus where the effective length of the thread is narrowly
prescribed.

It is important not to leave the active parts of the thread
appreciably silvered, for the sake of avoiding zero changes due to the
imperfect elasticity of the silver. In this soldering process
ordinary tinman's solder may be employed; it must be applied very
free from dust or oxide.

Sec. 91. Other Modes of soldering Quartz.

Thick rods of quartz may be treated for attachment by solder in the
same way as glass was treated by Professor Kundt to get a foundation
for his electrolytically deposited prisms. [Footnote: See Appendix at
end of book.]

The application of a drop of a strong solution of platinum
tetrachloride to the rod will, on drying, give rise to a film of the
dry salt, and this may be reduced in the luminous gas flame. During
the process, however, the quartz is apt to get rotten, especially if
the temperature has been anything approaching a full red heat. The
resulting platinum deposit adheres very strongly to the quartz, and
may be soldered to as before. This method has been employed by the
writer with success since 1887, and may even be extended to thick
threads.

It was also fo