Improvements in Electric Heating Devices.
Year: 1897

page_text: Date of Application, 15th Dec., 1897-Accepted, 15th Jan., 1898
COMPLETE SPECIFICATION.
Improvements in Electric Heating Devices.
I, FERNAND LE ROY, of 60, Rue Cortambert, Paris, in the Republic of France,
Engineer, do hereby declare the nature of this invention and in what manner the
same is to be performed, to be particularly described and ascertained in and by the
following statement:―
Electric heating is based on the well known property possessed by conductors of
becoming heated on the passage of a current. It is generally admitted that the
quantity of heat given off is furnished by Joule's law and if this quantity of heat
be indicated by q, the resistance of the conductor by R and the intensity of the
current by I and a co-efficient, which is as is well-known the mechanical equivalent
of heat by A, there is obtained
being the specific resistance of the conductor, its length and s its section.
In order to render q as large as possible for a given value of I efforts have been
made to increase R within possible limits.
the
The use of metallic conductors has numerous drawbacks, in fact by reason of
the low specific resistance r of metals it has been found necessary to increase
length of the conductor and diminish as far as possible its section s. The result has
been that heating devices have been formed which by reason of their nature, form
and consistency can only be used when enclosed in an insulating substance and
the heat developed by the passage of the current is not utilized by direct radiation,
and further such devices rapidly deteriorate.
In order to avoid these drawbacks I form heating devices by employing a body,
of considerable specific resistance r which enables the length of the conductor to,
be decreased and its sections increased and further, owing to their consistency, form
and dimensions, the large quantity of heat given off may be utilized by direct:
radiation.
Recent experiments and trials have enabled me to ascertain that Joule's law
does not give a perfectly exact equivalent of the quantity of heat developed in a
conductor by the passage of a current of a given intensity. I have ascertained that
this quantity of heat for a given body is not simply proportionate to the specific
resistance of such body but it varies according to the specific heat of the body
and also according to the chemical action produced by the
of the current,
passage
such for instance as oxidation.
Such a chemical action may modify more or less the quantity of heat evolved
not only by the fact of its production itself but also by reason of the transforma-
tion of the device in consequence of deposits, compounds or other phenomena which

page_text: may be discovered by a rapid modification of the specific resistencer and con-
sequently of the effective resistance R of the body.
Struck by these results and the inconveniences resulting therefrom for the use
of heating devices such as those hitherto employed, I have conceived the idea of
obtaining electric heating by means of the insulated and portable devices which
form the object of the present invention, an example of which is shown in the
accompanying drawing.
I have devised a heating device consisting of a rod of high specific resistance,
the heating of which rod may be utilised by direct radiation whilst the device
remains entirely unexposed to the chemical action of the surrounding medium.
For this object I form the device by placing a bar A (cylinder or prism) of silicon
pure or in combination (similar to the heating bodies described in my previous
patent 23354/95) in a tube, -sleeve, or cylinder B preferably of glass capable of
resisting the highest temperatures and of suitable form, in which I form as perfect
a vacuum as possible. The bar A has at each 'end a socket a a¹ at which the con-
ducting wires E and S terminate, which wires pass, through breech pieces or
supports C C connected by a suitable cement to the ends of the cylinder B. Instead
of forming a vacuum in the sleeve B which contains the resistance proper I can
also fill said sleeve with a reducing or, inert gas. Such an appliance in addition
to its better constitution. from the point of view of the utilisation of the heat
evolved, has the advantage of being easily transportable and disconnectable and
capable of being arranged with the, greatest facility for heating a room or a
culinary utensil, being placed in circuit with any suitable wire by simply,connect-
ing the wires E and S to terminals. It is of course needless to state that the form
and dimensions of the tube B and the end pieces or supports C may receive such
modifications as will cause them to better suit the special uses for which these
improved heating devices are intended. A larger or smaller number of these
improved devices may be grouped to form a stove, radiating. hearth or the like
apparatus.
The bar A placed in the glass tube is formed of any suitable body forming a
resistance and prepared in any suitable manner according to its nature. When I
employ silicon bars or blocks, they are obtained by compressing silicon powder
under strong pressures with or without an agglutinant and baking the bar or block
thus prepared. The resistance placed in the tube may be any suitable one but I
employ silicon by preference.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare, that; what, I
claim is
1. As a new article of manufacture-an-insulated heating device 'constructed sub-
stantially as herein before described with reference to the 'accompanying drawings.
2. An improved electric heating device consisting of a resistance placed in a
casing or sleeve of suitable material said-sleeve having a vacuum in its interior
or being filled with a reducing or inert gas with the object of protecting the resist
ance against the chemical action of the surrounding medium, the whole forming
a-heating device convenient to handle and capable of being connected with any
suitable wire, substantially as hereinbefore described.
1.
Dated this 14th day of December 1897.
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W. P. THOMPSON & Coast in tarar ve}
Of 6, Lord Street, Liverpool, Agents for the Applicant.
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