Year: 1889

page_text: Date of Application, 1st Jan., 1889
Specification Accepted, 16th Feb., 1889
We WILLIAM SCARLETT DE LISLE ROBERTS, and JAMES SMITH MOLLISON, both of
Sydney, in the Colony of New South Wales, Civil Engineers, 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:―
This invention relates to certain improvements in the construction of those Thermo-
electric Generators where Thermo-electric couples are used.
The first part of our invention consists of a stove or furnace which is surrounded by
an air-tight hot-air chamber, the outer walls of which are composed of any suitable
non-combustible insulating material (preferably a mixture of fire clay and asbestos).
The couples are so inserted into the insulating wall, that for a portion of their length
they shall project into the hot air chamber. The heat in this chamber is regulated by
a pyro safety valve fixed in any convenient position in the upper part of the chamber.
All risk of overheating the chamber will thus be avoided, and a uniform heat imparted
to the couples that project within the hot air chamber.
The invention further relates to a novel mode of making the thermo-electric couples,
without any joint or soldering at the junction of the metals.-This is effected, during
the process of casting, by fusing the two metals together. By adopting this mode of
forming the couples, the inconvenience hitherto experienced from the extra resistance
and consequent diminution of the electric current, due to the loosening of the joint by
unequal expansion and contraction of the metals, will entirely cease.
In carrying out the Invention, a furnace or stove of any convenient form may be
employed, but for the generation of a large current of electricity for lighting public
buildings or streets, it is preferable to use a long narrow stove, the length being
proportional to the size of the furnace. The stove or furnace is surrounded by an air
space, which is enclosed, on its outer side, by a wall composed of any suitable
insulating non-combustible material, preferably a mixture of fire clay and asbestos.
Into this insulating wall are fixed the thermo-electric couples which should project
within the air space for a portion of their length, for reasons hereinafter more
particularly specified. In order to prevent overheating in the air chamber, a pyro
safety valve and pyro gauge of any suitable design, are placed at the highest part of

page_text: the air chamber. Although no particular design of pyrometer is specified, it is
preferable to employ one composed of two metals which expand in different ratios,
such as cast iron and zinc. On the air chamber becoming heated to the limit of
safety, the pyro safety valve is so adjusted that the expansion of the zinc or other
metal shall lift the pyro safety valve, and thus allow the overheated air to escape,
while at the same time permitting cold air to enter the chamber through a valve
placed near its lowest part. Or, without diminishing the efficiency of the apparatus
to any perceptible extent, an inlet passage near the lowest part of the air chamber
may be kept permanently open.
In constructing thermo-electric couples, the mode usually adopted hitherto has been
to solder the ends of the elements to the negative and positive connecting pieces. or
to simply cast the ends of the elements on to connecting pieces composed of such
metals as tinned iron or copper.-In making our thermo-electric couples, we do not
confine ourselves to the use of any particular metal or alloys, but we employ two
metals or alloys that melt at different temperatures. The metal or alloy of which the
connecting pieces are formed, should melt at a lower temperature than the metal or
alloy used for the elements. From experience we find that the metal and alloy that
give the best results are malleable zinc for the connecting pieces, and an alloy of
antimony and zinc for the elements. In order to thoroughly unite the two parts of
the couples, the malleable zinc connecting pieces are placed within a mould, and the
alloy of antimony and zinc cast round them as the zinc will melt at a slightly lower
temperature than the alloy of antimony and zinc, the malleable zine will, during the
process of casting, melt into the alloy, and will thus form one united whole, without
joint, and with an alloy at the ends of the elements containing a slight excess of zinc.
The couples thus constructed, are then placed in a frame, packed with the insulating
non-combustible material above referred to, and placed in the outer wall of the air
chamber which surrounds the furnace. The ends of the couples are made to
project a portion of their. length within the air chamber, so that the ends within
the chamber may be affected equally by the hot air circulating therein. The air
which becomes heated at the hottest or lowest part of the air chamber will ascend to
the highest or coolest part of the same, where, being partially cooled, it will then
descend, thus creating a circulation, which will continue until the temperature has
been equalized throughout the chamber. For domestic purposes, the couples may be
connected to an air chamber attached to an ordinary, cooking range, so that during
the process of cooking, the couples may convey the electricity generated, to a set of
electric accumulators, and the electricity there stored for subsequent use.
In the accompanying drawing,
Fig. 1 is a section of the form of furnace we propose to employ for medium and
large installations.
Fig. 2 is a plan of the same.
Figs. 3 and 4 shew our thermo-electric generator applied to an ordinary.cooking
stove, Fig. 3 being a sectional plan, and Fig. 4 an elevation, of the apparatus.
In Figs. 1 and 2, A represents the furnace, B the hot air chamber that surrounds
it, CC the thermo electric couples, which may be so arranged as to generate either
large currents, or great electro-motive force, as required. B is the pyro safety valve,
so arranged as to allow the overheated air to escape, E the pyro gauge to indicate
the rise or fall of temperature within the air chamber; F is the furnace chimney or
uptake.
In Figs. 3 and 4, representing a domestic cooking range (which may be connected
with a set of electric accumulators), I is the fire grate; K K-is the flue area for
heating the oven and the hot air chamber B.
The thermo-electric couples are shewn at M M, projecting, as before described, a
portion of their length into the hot air chamber B.
Fig. is a perspective view of our thermo electric couples, the two parts of which
are composed of metals or alloys that melt at different temperatures. In this view,
mm are the positive and negative connecting pieces, composed preferably of malleable
zine nn are the elements composed preferably of an alloy of antimony and zinc,

page_text: which melts at a much higher temperature than the zine. The ends of the zinc
connecting pieces are inserted into a mould, and the alloy of antimony and zinc cast
round them; the result will be that the zinc ends will partially fuse and combine
with the alloy of antimony and zinc, forming at the two ends of the elements a second
alloy of antimony and zine, having a slight excess of zinc. The couples will thus be
rendered more effective and durable.
Having now particularly described and ascertained the nature of our said
invention and in what manner the same is to be performed we declare that what
we claim is―
1. In thermo-electric generators, the hot air chamber in combination with the
projecting thermo-electric couples, substantially as described and as illustrated in the
drawing.
2. In thermo-electric generators, the combination of the hot air chamber and
thermo-electric couples with a pyro safety valve and pyro gauge, substantially as
described, and for the purpose herein set forth.
3. Making thermo-electric couples of two metals or alloys which melt at different
temperatures, so that the metal or alloy of which the element is composed shall, while
in process of casting, cause the partial fusion of the metal or alloy of which the
connecting pieces are composed, and another alloy be thus formed at the point of
union of the metals or alloys, substantially as described, and for the purpose herein
set forth.
Doted this 1st day of January 1889