An Improvement in Thermometers.
Year: 1894

page_text: Date of Application, 27th Apr., 1894
Complete Specification Left, 28th Jan., 1895-Accepted, 9th Mar., 1895
PROVISIONAL SPECIFICATION.
An Improvement in Thermometers.
I, JOSEPH KENT of 98 Hatton Garden, in the City of London Clerk, do hereby
declare the nature of this invention to be as follows:-
This invention relates to an improvement in the thermometers for which former
Letters Patent dated the 25th day of November 1890 No. 19199 were granted to
me, and has for its object to overcome a difficulty which is experienced in the
manufacture of such thermometers wherein a scale marked strip is received in a
flattened bore in the stem in rear of the mercury column with the object of avoiding
the liability of the scale being defaced or destroyed, to which the usual external
graduations and markings are exposed.
The difficulty I have experienced in manufacturing such thermometers arises
from the liability of the tube cracking when the enamel scale marked strip is being
sealed up in the bore of the stem. To overcome this difficulty substitute a scale
marked strip of mica for the enamel strip and provide the stem with an enamel
backing sufficiently opaque, and at the same time of a sufficiently translucent
character to enable the scale, owing to the translucence of the mica itself to
be read off with the greatest ease and accuracy, when the instrument is held up to
the light.
The mica strip is secured in the bore by being sealed into the glass of which the
thermometer stem is formed and in this respect differs from the enamel strip
heretofore proposed to be used inasmuch as the mica strip being able to withstand
the high temperature of molten glass is embedded in and gripped by the glass in
such manner that it cannot possibly shift and being flexible and tenacious cannot
possibly break off whereas the enamel was not able to withstand the temperature
necessary to enable it to be welded to the glass. The mica scale being unaffected
by the great heat to which chemical thermometers more especially are exposed, it
is not liable to variation and is practically indestructible.
Dated this 27th day of April 1894.
An Improvement in Thermometers.
I, JOSEPH KENT of 98 Hatton Garden in the City of London Clerk, 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 an improvement in the thermometers for clinical,
chemical and industrial purposes for which former Letters Patent, No. 19,199,
dated the 25th of November, 1890, were granted to me, and in which a scale
) marked strip is contained in a flattened bore in rear of the mercury column, and it
LD

page_text: has for its object to provide a thermometer of this class in which the scale, besides
being protected from the corrosive action of acids, is unalterable and is absolutely
fixed in position with relation to the mercurial or other column, which is not the
case with such thermometers as heretofore made.
A scale marked strip enclosed within a second bore in rear of the capillary bore,
and secured therein by one end being sealed into the glass of which the stem is
made; must be made of a material whose co-efficient of expansion and contraction
corresponds to that of the glass stem of the thermometer in order to ensure proper
correspondence of the scale with the length of the capillary column at various
temperatures, and this material must be of such a nature that it will be absolutely
unaffected by the fusing temperature of the glass in the operation of sealing it into
the thermometer stem, and it must be transparent in order that the readings of the
thermometer may be visible by transmitted light, the utility of which in clinical
thermometers will be hereafter referred to.
In order that the readings may also be clearly visible by reflected light, it is
also necessary that the transparent scale-strip be backed by white enamel which
must be translucent to permit of the reading by transmitted light and must be
protected from the attack of corrosive agents.
The present improvements, therefore, consist in the construction of the scale-
strip of a special material which alone of all known materials of which such a
scale-strip could be made possesses the necessary qualities for the purpose. This
material is mica, which is easily split into thin transparent lamiuæ and cut of
the requisite length and breadth, and upon which the markings of the scale
with the usual enamel paint may be readily made and fixed by heat in the
usual way.
"
The mode of making double bore stem or tube consists in blowing the "ball"
for the capillary tube, and blowing another, but much lighter, "ball or cylinder
with a very much larger bore to form the scale tube, then manipulating the latter
to bring the bore to the required oblong shape in cross-section and of the proper
relative proportion to the bore of the other "ball," then whilst both "balls are
still in the semi molten state they are caused to adhere together. A strip of white
translucent enamel is then applied to the back of the last mentioned "ball" to
form a backing for the scale bore. In this state the bores of the two "balls are
of the proper relative sectional areas and shapes, so that when the united "balls"
are drawn out to form a tube of the requisite diameter the bores will preserve their
relative proportions, shape, and position.
"
"
Before the united "balls are thus drawn they are "covered" by being dipped
into molten glass which thus covers both "balls" and encloses the enamel strip
and this soft glass covering is then marvered in order to bring the united "balls
to the required form externally, without thereby altering the internal form of their
bores. The united "balls" with enamel stripe applied and covered with plain
- glass, are then drawn out to form a double bore tube, the one bore being the usual
capillary bore and the other a flat bore of a width many times greater than the
* capillary bore, and large enough to receive the mica strip, or, say, about 0.5 milli-
metres broad by about 4 or 5 millimetres wide, backed by a white enamel strip
embedded in and drawn out with the glass.
The tube having been thus made, a bulb is blown on one end of the capillary
bore in the usual way and the adjacent' end of the scale bore is sealed up, the other
end being left open.
The bulb and capillary bore having been filled with mercury or other fluid, and
the capillary bore sealed in the usual way of making thermometers, and the mica
strip having been divided and marked with reference to the position of the
fluid in the capillary bore at various temperatures, this scale strip is then inserted
in its bore and is sealed up and fixed therein by fusing the glass of the stem which
surrounds the end of the mica strip and compressing it around the end of the mica
strip to which the molten glass adheres so as to fix it securely in position.
It has heretofore been proposed to make such scale strips of enamel, but as the

page_text: enamel could not withstand the high temperature of fused glass necessary for
welding it to the enamel, it could only be fixed by heating the glass of the
thermometer stem to such a comparatively low heat as to enable it to be
merely softened and pinched in upon the enamel strip which was consequently
beld very insecurely so that it was liable to fall out of position and as the
enamel was very brittle it was liable to be easily broken off by shock, the
thermometer thus being in either case rendered useless, whereas the mica strip
is quite unaffected by the heat of molten glass which adheres firmly to it so
that it, is effectually secured in position and being flexible and tenacious it
cannot possibly break off. To remedy the defect referred to and provide a
thermometer with an enclosed translucent scale which can be read by transmitted
light is of great importance for clinical purposes, since the indication of the
instrument can be read off with precision in a darkened sick-room by merely
viewing the instrument when lighted from behind by a feeble light, such as the
flame of a match or candle.
The accompanying drawing illustrates a cross-section of the stem of the improved
thermometer, drawn to a highly magnified scale.
a is the capillary bore situated at about the axis of the stem which is formed
with the usual curved or lens-like front b, the thickness of the glass in front of the
bore a and the curvilinear form of the front surface 6 being such as to magnify both
the indicating column of fluid in the capillary bore, and also the scale situated
directly behind it. c is the bore in which is received the scale strip d of mica,
which, as well as its bore, is of very great width relatively to the bore a, so that the
markings of the scale shall be very legible. e is the strip of white enamel
embedded in the substance of the glass behind the scale bore c and corresponding
in width thereto, so as to form an effective backing for the markings on the
transparent scale.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed, I declare that what
I claim is :-
1st. A thermometer for clinical, chemical and industrial purposes having a
transparent scale-marked strip of mica sealed up and held in position in a broad
flat bore, immediately in rear of the capillary bore, by fusing the glass to the strip,
in combination with a stripe of white enamel embedded in the glass in rear of the
bore for the scale strip, substantially as specified.
2nd. In a thermometer of the kind described the application of mica as the
material for the scale marked strip sealed up in the stem by fusing the glass to it as
described.
Dated this 28th day of January 1895.
A. M. & WM. CLARK,
53, Chancery Lane, London, Chartered Patent Agents.