IMPROVEMENTS IN MICROPHONIC CONDUCTORS OR CONTACTS AND IN THE PREPARATION OF MATERIALS FOR SUCH CONDUCTORS OR CONTACTS
Year: 1882

page_text: PROVISIONAL SPECIFICATION left by John Henry Johnson at the Office
of the Commissioners of Patents on the 2nd May 1882. A communication
from abroad by Doctor Arsène D'Arsonval of Paris in the Republic of
France
JOHN HENRY JOHNSON of 47 Lincolns Inn Fields in the County of Middlesex
Gentleman "IMPROVEMENTS IN MICROPHONIC CONDUCTORS OR CONTACTS AND IN
THE PREPARATION OF MATERIALS FOR SUCH CONDUCTORS OR CONTACTS
"
a com-
munication from abroad by Doctor Arsène D'Arsonval of Paris in the Republic of
France
This invention relates to the preparation of substances which possess the
necessary properties for forming efficient microphonic conductors or contacts and to
their application for this purpose
My foreign correspondent has discovered that it is possible to employ as
microphonic conductors or contacts substances prepared as hereinafter described in
the place of the carbon or graphite ordinarily employed for this purpose or in
place of the metallic powder and liquids which have heretofore been sometimes
substituted for the carbon.
In order to obtain good results from a microphonic conductor or contact it is
necessary that the conductibility or conducting power of the said conductor should
change as much as possible with a given variation of pressure; moreover, it is
necessary that the molecular condition of these bodies should be such as to prevent
the objectionable effects which are liable to be produced at every change of
potential when imperfect conductors and contacts are employed.
It has been acknowledged that in order to obtain substances fulfilling these
conditions it is necessary to select materials composed of perfectly homogenous
molecules and it was believed that these conditions could not be complied with
except by the employment of carbon in the highest possible condition of purity in
which it is possible to obtain it commercially without impairing its conducting
power such as graphite, plumbago, artificial carbon or by the employment of
metallic powder or liquids.
By means of this invention the required degree of homogeneity is obtained by
fusion so that it is rendered possible to employ for microphonic purposes such

page_text: materials as manganesian agglomerates, as well as sulphides, bisulphides and
oxysulphides with or without an excess of metal or sulphur.
In order to prepare these materials or substances for the purpose of forming the
improved microphonic conductors or contacts they are treated as next hereinafter
described.
A metallic sulphide, such as sulphide of iron, copper, lead or silver for example,
with or without an excess of inetal is melted in a crucible; in certain cases a
metallic oxide is added or a mixture of sulphides of different metals is prepared.
These sulphides when melted may be employed either alone or as the cover or
coating of a metal which affords them support either by dipping the metal into the
molten sulphide for example or by superficially sulphurising the metal itself by
exposing it to be acted upon directly by sulphur in a fused or gaseous condition or
by any known chemical process of sulphurisation.
It is preferred to employ tempered or hardened steel as a metallic support as this
material is capable of being rendered magnetic after the superficial sulphurisation
This preliminary magnetisation of the support enables the microphonic contact
to be effected by magnetic attraction and thus enables the spring or weight
usually employed to keep the bodies forming the microphone in contact to be
dispensed with.