Evening star., 1925-01-05
VALUABLE METALS
NOW USED IN RADIO
Engineers See Real Worth in
Platinum, Silver
and Gold.

Gold-plated buswire, sterling silver
contact points and solid platinum cat
whiskers are among the latest radio
novelties. To many radio constructors
these things seem merely extrava
ganceSs Other engineers contend that
real and important benefits are OBJ
tanned from the use of these precious
metals. There is talk of the greater
electrical conductivity of silver and
of the improved electron emission
from platinum.
The truth of the matter is that these
three metals-gold, platinum and sill
ver-derive whatever value they pos
sess for radio use entirely from the
ways in which they are affected by
the air. 1t is the surface corrosion
film that forms Cor does not form) on
them that makes them of interest to
the radio constructor
When copper wire-as. for example,
the wire wound on a coils exposed
to the air there forms slowly on it's
surface a very thin surface layer of
copper sulphide. This layer will form
even underneath the wrappings OF a
silk-covered wire, for the silk threads
are permeable to the air, and the
gases that produce the copper sui
phide get through them. SO far as
concerns the direct current resistance
of the copper wire this does not mat
ter. The decrease in effective diane
ter of the wire due to the sulphide
film is altogether negligible.
But for radio frequency currents
this may not be true. Such currents
travel mainly near the surface of the
conductor This is what is called the
Skin effect" Accordingly a poorly
conducting layer of copper sulphide
on the surface of a wire may alter
considerably the resistance of the
wire for radio frequency currents. It
is not possible to say that 1t does
alter the resistance. for no one has
ever worked out the matter expert
mentally.
Silver Is Good Conductor.
Now, when silver wire is exposed
to the air it forms a coating of silver
sulphide in very much the same way
as copper does. But this silver coat
ing unlike the copper coating, is a
good conductor of electricity-almost
as good as is the metallic silver itself.
Accordingly, a siIver-wire coil may
be better for radio than a copper coil
is. Again, we cannot say that II is
better Precise experiments have
never been made.
Now for the catwhiskers. We are
informed by several eXperimenters,
notably by Or. JOnn B- Buenltr OF
Los Angeles, that actual experiments
show a substantial advantage in the
use of a catwhisker made Of gold or
platinum wire over one made of cop
per or brass or bronze wire This,
too, may be an effect of surface films
Gold alters in air only very slightly;
platinum scarcely at all. Nobody
knows the theory of how the crystal
detector works. but we do know that
very thin, invisible films of dirt or oil
or of many other things will affect
the operation of the crystal very
seriously. Perhaps the same is true
of the film of copper sulphide that
forms over the point of catwhisker er
made of copper or of copper alloys
Perhaps gold, lacking this film, pro-
videS a better contact or a contact
more suitable in some manner for
the rectifying action upon which the
operation of the crystal depends.
No field in radio cries so loudly for
precise investigation as does this one
of the effect OF air-formed surface
films on the behavior of radio appa-
ratus. Sareful and patient studies ot
the effects Of known surface films on
known metals used as wires or cat
whiskers would undoubtedly be valu-
able both theoretically and practi-
cally.
Copyright. 1925, Popular Radio, Incl