Improvements in Thermometric Circuit Closers or Alarms.
Year: 1895

page_text: Date of Application, 21st Mar., 1895
Complete Specification Left, 4 h Dec., 1895-Accepted, 4th Jan., 1896
PROVISIONAL SPECIFICATION.
Improvements in Thermometric Circuit Closers or Alarms.
1, RICHARD PEARSON, of 2, Great St. Helens, in the City of London, Engineer,
do hereby declare the nature of this invention to be as follows:-
My invention relates to an improvement in thermometric circuit closers or
alarms of that kind in which an electric circuit is closed by contact of the mercurial
column with platinum wires sealed into the glass. Usually one of these wires is in
constant contact with the mercury whilst the other enters the thermometer at
a point in the length of the tube, but the objection to this arrangement is that the
platinum wires become destroyed in course of time, the first mentioned by contact
with the mercury and the other by being exposed to vapours or fumes given off from
the mercurial column.
According to my improvement, I seal the contacts into the upper or vacant part
of the thermometer tube so that neither is constantly in contact with the mercury,
and interpose between the mercury column and the contacts a short column of a
fluid, such, for instance, as creosote or any suitable hydrocarbon, which acts as a
lubricant, and by covering the end of the mercury column prevents the emanation
of fumes or vapours into the tube. The mercury column may either be the
thermometric fluid or merely the index propelled by the expansion of another fluid,
and the thermometer may be of the ordinary straight, or of the bent, form usual for
maximum and minimum thermometers, and the contacts may be so arranged that
the circuit will be closed at either of two limits of temperature.
Mash 1805
A. M. & WM. CLARK,
53, Chancery Lane, London, Chartered Patent Agents.
A. M. & WM. CLARK,
53, Chancery Lane, London, Chartered Patent Agents.
COMPLETE SPECIFICATION.
Improvements in Thermometric Circuit Closers or Alarms.
I, RICHARD PEARSON, of 2, Great St. Helens, in the City of London, 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 :-
My invention relates to thermometric electric-circuit closers of that kind in
which the closure is effected by the contact of the mercurial column with platinum
contact wires, one of which has always hitherto been in constant contact with. the
mercury whilst the other wire entered the bore of the thermometer at, or extended
therein to, a point not reached by the mercurial columu at normal temperatures.
The objection to this arrangement is that the platinum wires become rapidly
destroyed, the one in constant contact with the mercury becoming amalgamated aud
dissolved, and the other when contained in a dry tube, whether closed or open.
becoming covered with oxide of mercury resulting from oxidation of the vapours or
fumes given off from the mercurial column by the oxygen of the air or residual air
contained in the thermometer tube.
According to my improvement both of the platinum contact wires forming the

page_text: terminals of the alarm circuit enter the thermometer tube at such a point or points
that neither wire shall normally be in contact with the mercury, and there is
interposed between the mercury column and the said wires or contacts a short
column of an insulating fluid which will prevent the emanation of fumes or vapours
into the tube; the fluid being by preference of such a nature as to act as a lubricant
for the bore and contacts and avoid liability of the mercury column breaking when
the temperature falls again after being raised. In this insulating column the ends
of the platinum wires may be constantly bathed.
The thermometer may be of the ordinary straight form, and the mercury column
may itself be the thermometric fluid if it be required to close the circuit only on the
rise of temperature to a given point as in the case of a fire-alarm; or the mercury
column may be merely propelled by the expansion of another fluid acting as the
thermometric fluid, the mercury being in that case used only for the purpose
of closing the electric circuit or circuits as in some maximum and minimum
thermometers in which case the contacts may be duplicated so that a circuit will be
closed on the attainment of either of two limits of temperature as required for
horticultural, medical, and other purposes.
Reference is to be had to the accompanying drawings forming part of this
Specification which shew on a scale about twice full size in Figure 1 a fire-alarm
whereby the alarm will be given on the attainment of an abnormally high
temperature and in Figure 2 a thermometric alarm whereby the alarm will be given.
on a rise or a fall of temperature beyond predetermined limits.
In both cases the thermometer is shewn as of U shape and is provided with a pair
of contacts a, a¹, formed of platinum wires sealed through the glass of the
thermometer stem and entering the bore at a point or points not reached by
the mercurial column c at normal temperatures but only when it is moved along the
bore by the expansion under an excessive temperature of the thermometric fluid
contained in the bulb d. The part of the bore where the contacts a, a', are situated
is occupied at normal temperatures by an insulating liquid which may be an
alcohol usually employed but it is preferred to employ creosote prepared as
hereinafter described or other heavy hydrocarbon which acts as a lubricant and
preserves the contact wires from attack by emanations from the
the space
within the small bulb e being the usual vacuum.
mercury,
The contacts a, a', may be directly opposite each other, as shewn, or not and they
are formed preferably by bending back the ends of the platinum wires so that they
lie along the interior of the bore for a short distance. They are connected to the
binding posts p, p', and form the terminals of an electric circuit including a bell or
other alarm or indicator. The lubrication of the contacts is important as it avoids
liability of a globule of mercury breaking off from the end of the column and,
by adhering to the contacts, permanently closing the circuit when the temperature
falls again after a rise.
In Figure 2 there is in addition to the pair of contacts a, a', a similar pair
of platinum wire contacts h, 61, sealed into and entering the stem between the main
bulb d and the mercury column at a point or points only reached by the latter at a
temperature at which the low temperature alarm is to be given.
The thermometric fluid contained in this part of the stem and the bulb d is
in' this case also an insulating fluid and may be alcohol, but is preferably creosote
or a heavy hydrocarbon prepared as herein described by which the contacts b, b¹,
are lubricated and preserved from injurious action by the mercury. These contacts
are connected to the terminals p', p', of a circuit containing a bell or other alarm or
indicator by which warning of a fall of temperature will be given.
As the contacts b, b¹, are not required for the purposes of the fire alarm shewn in
Figure 1, the thermometric fluid in d might in that case be mercury, but having
regard to the large size of the bore used when the contacts are placed opposite one
another (namely a diameter of about two millimetres) mercury would not usually be
employed as the thermometric fluid even for a tire-alarm in consequence of the
large size of the bulb which would be required.

page_text: For the purposes of this thermostatic circuit closer wood creosote is maintained
at a uniform temperature of about 300 degrees Fahrenheit, in order to volatilize
and eliminate the lighter hydrocarbons, the fatty matters which collect at the
surface being skimmed off from time to time and this treatment being continued
until the creosote acquires a boiling point of about 400 degrees Fahrenheit and a
specific gravity of about 107 under normal atmospheric conditions.
Having now particularly described and ascertained the nature of the said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is :-
1. A thermostatic electric circuit closer, consisting of a thermometer containing a
mercurial column, two platinum wires forming the terminal contacts of the circuit
and both entering the same thermometer bore at such a point that neither is
in contact with the mercury column at normal temperatures, and a column of
insulating fluid contained in the bore between the mercury and the said contacts
so as to protect the latter from the action of the mercury, substantially as
specified.
2. A thermostatic electric circuit closer, consisting of a thermometer containing
a mercurial column, two platinum wires both entering the thermometer bore at such
a point that neither is in contact with the mercury column at normal temperatures,
and a column of creosote or heavy hydrocarbon prepared as herein described,
contained in the bore between the mercury and the said contacts so as to protect
the latter from the action of the mercury and lubricate the contacts and the bore,
substantially as specified.
3. A thermostatic electric circuit closer, consisting of a maximum and minimum
thermometer containing a mercurial column, two pairs of platinum terminal
contacts each pair entering the bore of the thermometer at a point situated beyond
the mercurial column at normal temperature, and columns of insulating fluid each
normally interposed between a pair of contacts and the mercury, oue of said.
columns acting also as the thermometric column, substantially as specified.
Dated this 4th day of December 1895.
A. M. & WM. CLARK,
53, Chancery Lane, London, Chartered Patent Agents.
A. M. & WM. CLARK,
53, Chancery Lane, London, Chartered Patent Agents.