Chemical Society_ for September, 1920. In one of these methods
the glass is coated with platinum by covering it with a suspension of
platinum chloride in oil of lavender and heating until the oil is burnt
off. The metal tube is then tinned on its inner side and soldered to the
prepared glass, slightly acid zinc chloride being used as a flux.

In the second method, a joint is made by means of the Kraus flux, which
consists of equal weights of zinc oxide, borax, and powdered soda-glass
fused together. This is coated on the inner surface of the metal tube,
and the hot glass tube, which has had the end slightly flanged to give
support, is inserted. Fusion of the flux is completed by heating the
outside of metal tube.

_Silvering Glass._--In all cases where it is intended to deposit a
silver mirror on a glass surface, thorough cleaning is essential.
Prolonged soaking in a hot solution of potassium bichromate which has
been acidified with sulphuric acid will often prove useful. The glass
should then be washed thoroughly, rinsed in distilled water, and the
solution should then be used.

There are many formulae for the silvering solution, but that used in
Martin's method may be given:--

A--Nitrate of Silver 40 grammes
Distilled Water 1000 c. cm.

B--Nitrate of Ammonium 60 grammes
Distilled Water 1000 c. cm.

C--Pure Caustic Potash 100 grammes
Distilled Water 1000 c. cm.

D--Pure Sugar Candy 100 grammes
Distilled Water 1000 c. cm.

Dissolve and add:--

Tartaric Acid 23 grammes

Boil for ten minutes, and when cool add:--

Alcohol 200 c. cm.
Distilled Water to 2000 c. cm.

For use take equal parts of A and B. Mix together also equal parts of C
and D in another vessel. Then mix both liquids together in the silvering
vessel and suspend the glass to be silvered face downwards in the
solution. Or if a vessel has to be silvered on the inside, the solution
is poured in. In this case, the deposition of silver may be hastened by
immersing the vessel to be silvered in warm water.

In working with a silver solution containing ammonia or ammonium salts
there is sometimes the possibility of forming an explosive silver
compound. It is well, therefore, to avoid keeping such solutions longer
than is necessary, and to bear in mind that any deposit form