An Improvement in the Manufacture of Thermometer Tubing.
Year: 1895

page_text: Date of Application, 13th July, 1895
Complete Specification Left, 23rd Oct., 1895-Accepted, 23rd Nov., 1895
PROVISIONAL SPECIFICATION.
An Improvement in the Manufacture of Thermometer Tubing.
I, FRANCIS SAMUEL. TOMEY, of 142, Victoria Road, Aston, Birmingham, in the
County of Warwick, Glass Tube Manufacturer, do hereby declare the nature of this
invention to be as follows:-
This invention relates to the manufacture of tubing for clinical, chemical, and
other thermometers that are intended to have the graduations or divisions and
figures of the thermometric scale etched upon the rear part of the stem.
With this object in view it has long been desired to draw the tube with a very
thin external coating of enamel applied preferably upon a flat surface which when
the thermometer is finished would form the back of the stem and upon which surface
the scale would be etched. A thermometric scale so produced would be practically
indestructible, since the divisions and figures being etched through the enamel the
scale would be visible even should all the black filling be removed by acids or by
cleaning.
66
It has not, however, been possible to produce commercially, and by the ordinary.
methods of manufacture, enamelled thermometer tubing suitable for the purpose of
being so etched, owing to the impossibility of applying a sufficiently thin coating
of enamel to so extended a surface as that of what is known in the trade as the
'piece." The ordinary method of applying the enamel is to gather the required
quantity on to a pontil and flatten it, then to warm it again at the pot mouth, and
while very hot to apply in the required position, but it has heretofore been found
that when the enamel has been flattened thin enough for the desired purpose, it has
invariably run into corrugations immediately upon being exposed to the heat
preparatory to being applied to the required position on the piece to which it
never could be applied without air blisters being left between itself and the flint
"metal," and without such unevenness in the thickness of the coating of enamel as
to cause it to break while being drawn out. Even were it found possible to apply
a sufficiently thin coating of enamel to the piece and that the piece so coated were
drawn out in the form of a thermometer tube the thickness of the enamel has
unavoidably been so variable as to render impossible the proper performance of the
etching operation, inasmuch as it is not practically possible to obtain sufficient
action of the acid to produce the required depth of etching on the parts where
the enamel is thick, and yet prevent excessive action of the acid where the enamel
is thin.
To overcome these difficulties I blow the ball and form the bore in the usual way
omitting however the enamel. I then cover the ball with "metal" to the required
thickness and marver it to a cylindrical form, then having reheated it I carefully
Hatten the back of the piece upon a marver or other suitable surface.
I then dip
the piece carefully into the enamel, taking especial care to prevent contact of the
enamel with any but just the flattened surface of the piece, and having allowed the
enamel to drain off i carefully draw the flat surface of the piece over a knife or
scraper (fixed in the mouth of the enamel pot) before the enamel on the piece has
had time to become chilled in the slightest degree. All the superfluous enamel is
thus removed from the coated flat side of the piece, the enamel coating being left in
the form of a perfectly flat film of absolutely uniform thickness and free from
blisters. The piece is then marvered and heated and drawn out in the usual way.

page_text: It is to be observed that the enamel in which the piece is thus dipped must be
very hot and as fluid as possible, and inust be of such a composition that its
coefficient of contraction and expansion under variations of temperature will be the
same as that of the flint "metal"bf which the piece is made.
'Dated this 13th day of July 1895.
A. M. & WM. CLARK,
53, Chancery Lane, London, Chartered Patent Agents.
An improvement in the Manufacture of Thermometer Tubing.
1, FRANCIS SAMUEL TOMEY, of 142, Victoria Road, Aston, Birmingham, in the
County of Warwick, Glass Tube Manufacturer, 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 the manufacture of tubing for clinical, chemical, and
other thermometers that are intended to have the graduations and figures of the
thermometric scale etched upon the rear side of the stem and visible (when viewed
from the front) upon a white enamel ground behind the bore.
It has long been desired to draw the tube with a very thin external coating of
enamel which when the thermometer is finished would form the back of the stem
and upon which the scale would be marked by etching through the enamel. Such
a thermometric scale, besides its other advantages, would be practically indestructible,
since the divisions and figures being etched through the enamel are permanently
visible by mere contrast of the etched lines and figures with the white enamel
without requiring the usual black filling which is liable to be removed in course of
time by acids or by cleaning.
It has not, however, been possible to produce commercially, and by the ordinary
methods of manufacture, thermometer tubing having a sufficiently thin and
sufficiently uniform coating of enamel to admit of being etched in a practical and
commercial manner. This is due to the impossibility of applying a sufficiantly
thin coating of enamel to so extended a surface as that of what is known in the
trade as the "piece.' The ordinary method of applying the enamel is to gather
the required quantity on to a "punty or pontil and flatten it, then to warm it
again at the pot mouth and while very hot to apply it in the required position, but
experience has heretofore shewn that when the enamel has been flattened thin
enough for the desired purpose it has invariably run into corrugations immediately
upon being exposed to the heat preparatory to being applied to the required position
on the "piece" to which it never could be applied without air blisters being left
between itself and the flint "metal" and without such unevenness in the thickness
of the coating of enamel as to cause it to break whilst being drawn out. Neither
is it possible to obtain a sufficiently thin and uniform coating of enamel by merely
dipping the "piece" into fluid enamel, since the quantity so taken up would
necessarily exceed by inany times the thickness required and it is practically
impossible to drain off the excess without allowing the enamel to run into such
irregularity of thickness as to render it quite unsuitable for the purpose.
Even
were it possible to apply a sufficiently thin coating of enamel to the piece" and to
draw out the "piece" so coated into the form of a thermometer tube, the thickness
of the enamel would unavoidably be so variable as to render impossible the proper
performance of the etching operation inasmuch as it is not practically possible to
etch through the enamel to the required depth where the enamel is thick and yet
prevent excessive action of the acid where the enamel is thin.
"

page_text: To overcome these difficulties I blow the ball and form the bore in the usual
way and I then cover the ball with ""metal" to the required thickness and marver
it to a cylindrical form, then having re-heated it I carefully flatten the back of the
"piece" upon a marver or other suitable surface. I then dip the "piece," carefully
and so as to just bring the flattened surface of the "piece" into contact with the
surface of the fluid enamel contained in a pot, taking especial care to prevent
contact of the enamel with any but just the Hattened surface of the "piece," and
having allowed the enamel to drain off for a few moments within the pot I carefully
draw the flat surface of the "piece," to which the enamel has been applied, over
a knife or scraper (fixed in or near the mouth of the enamel pot) before the enamel
on the "piece" has had time to become chilled in the slightest degree. All the
superfluous enamel is thus removed from the coated flat side of the "piece," the
enamel coating being left in the form of a perfectly smooth and absolutely uniform.
film whose thickness does not practically exceed that of a sheet of ordinary
note-paper, and free from blisters. The "piece" is then marvered and heated and
drawn out into the form of thermometer tubing in the usual way.
Instead, however, of flattening the "piece" before dipping in the enamel, it may
be dipped while in its cylindrical form (care being taken to avoid the enamel
spreading unduly over the surface of the "piece") drawn over a knife or scraper,
of corresponding shape, and then flattened, "the "piece" being then marvered and.
drawn out, as before.
It is to be observed that the enamel in which the "piece" is thus dipped must be
very hot and as fluid as possible and must be of such a composition that its
co-efficient of contraction and expansion under variations of temperature will be
the same as that of the flint "metal" of which the "piece" is made.
The accompanying drawings illustrate, roughly, the modus operandi.
Figure 1 is a cross section of the "piece," drawn about full size, wherein the dot
and dash line a represents approximately by its thickness that of the coating of
enamel applied to the "piece" by dipping and scraping. b is the bore.
Figure 2 illustrates the dipping operation, c being the "piece" as applied to the
surface of the enamel in the pot d which is suitably supported in the furnace in an inclined
position, as shewn, so as to admit of the "piece" c, carried by the blowing iron e, being
readily introduced and dipped by being merely applied to the surface of the enamel
in the pot. Figure 2 also shews the operation of removing the excess of enamel taken
up in dipping by drawing the enamel-coated surface of the "piece" over a knife-
edged scraper f fixed in or near the mouth of the pot. This scraper is preferably
made of retort carbon, ground to a true knife edge and made smooth and polished
after grinding, by means of black-lead. A copper scraper might, however, be
used.
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: :-
1. In the method of manufacturing enamelled tubing for thermometers, dipping
the surface of the "piece" (produced by blowing and covering a ball of flint in the
ordinary way) into enamel and scraping off the superfluous enamel, whilst very hot
and fluid, by drawing the enamel-coated surface over a scraper, so as to leave said
surface coated with a very thin and uniform film of enamel, as specified.
"
2. The herein described method of manufacturing enamelled tubing for
thermometers, which method consists in dipping the flattened surface of the "piece
(produced by blowing and covering a ball of flint in the ordinary way) into enamel
and scraping off the superfluous enamel, whilst very hot and fluid, by drawing the
enamel-coated surface over a scraper so as to leave a very thin film of enamel of uniform
thickness, as specified, and finally marvering, heating, and drawing the enamel-coated
piece" into thermometer tubing, substantially as described.
66
"
3. Thermometer tubing having the rear surface coated with a strip of enamel of

page_text: exceedingly minute but uniform thickness such as to be capable of having a scale
uniformly produced upon it by etching, as described.
Dated this 23rd day of October 1895.
A. M. & WM. CLARK,
53, Chancery Lane, London, Chartered Patent Agents.