IL23142A - Method of marking mercury glass thermometers - Google Patents

Description

'ΠΙΙΙΠ |Π3 ΤϊΙΠΙ"! 'Π PATENTS AND DESIGNS ORDINANCE SPECIFICATION Method of marking mercury glass, thermometers I (we) SEYMOUR NORMAN BLACKMAB , a citizen of the U.S.A. , of 431 Bast Palisades Avenue, Englewood, Bew Jersey, U.S.A. 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 a method of marking mercury glass thermometers.

Although my invention will be described hereinafter by way of example with respect to glass clinical thermometers, I wish to mention at this point that my invention is not so limited but pertains to the marking of all types of glass thermometers, that is to say, commercial glass thermometers as well as clinical glaes thermometers. Examples of commercial glass thermometers are: chemical melting point thermometers, water bath thermometers, outdoor thermometers, and boiler thermometers which in general are characterized by a glass stem of any shape of cross-section, e.g., circular, and by the presence or absence of a trap, and by temperature graduations on the stem itself.

A clinical, i.e. fever thermometer of either the rectal, oral or stubby type conventionally comprises a straight shaft of roughly triangular crossrsection with a rectilinear axial capillary bore therein that terminates at one end in a thin-walled reservoir bulb. The bulb contains a liquid which expands upon the application of heat, such, for instance, as mercury, the expansion, and, therefore, the temperature, bein measured by the rise of a column of the liquid in the capillary bore. Such thermometers customarily are made of transparent material, and almost invariably of glass. The actual cross-section of the thermometer is such that a rounded corner of the shaft acts as a lens to magnify the tiny diameter of the bore in which the liquid rises.

It should be observed that in some thermometers, usually commercial thermometers, where the capillary bore is somewhat larger than that of a clinical thermometer, it is not necessary to employ such a lens portion, ana, therefore, the stem may be of circula cross-section. and filled narking and a raised ceramic marking. The latest and most popular is a flush stained marking.

The etched and filled type of thermometer marking is subject to the drawback that the filling material, be it pigment or ceramic, tends to loosen and fall out which makes the thermometer difficult to read and opens pockets for co tamina ion. Moreover, and importantly, the removal of glass by etching leaves the thermometer locally weakened at each mark which thereupon acts as a focus for breakage. Thermometers with raised ceramic markings are subject to leaching of pigment from the raised markings and to chipping of the markings during day-to-day handling of the thermometer and to differential expansion, of the marking and glass shaft upon cooling after the firing which fuses the marking in place. Furthermore, when fragments of the marking1 chip off the glass shaft they take with them adhered fragments of the shaft which leaves the thermometer shaft locally weakened.

It also has been proposed, as shown in my United States Letters Patent No. 2,707,688 and in United States Letters Patent No. 2,811,01+0, to stain the shafts of &lass clinical thermometers.

In the earlier of these patents the staining was performed by induction heating and, although the ensuing thermometer was desirable by virtue of flush stained markings, the uneven heating of the glass shaft at the discrete points where the stain markings were incorporated into the glas3 left many stress points «as a result of which the thermometer was subject to easy breakage. It may be noted that such stressing could be avoided if the induction heating were carried out at a sufficiently low temperature, viz. about 600°F., instead of 780° , but this is commercially impractical because in such event the time cycle is subject to a serious commercial drawback, to wit, local removal at the marking points of the surface portions of the glass shaft by etching, the etched pockets subsequently being stained. Not only would the construction therein proposed leave a zone of weakness at each etched zone, but the method disclosed for heating the shaft while concurrently coolin the naercury bulb would leave a substantial residual stress in the zone between the bulb and the shaft which makes the thermometer particularly susceptible to breakage at this zone when subjected to shock or pressure.

I have, in ray United States latent No. 3,172,289 disclosed a thermometer which is not subject to any of the foregoing drawbacks.' Thus, in said thermometer there are no etched portions, there are no raised markings, there are no prohibitively high stresses at the markings and there is no zone of stress between the mercury bulb and the marked part, of the shaft. In this thermometer, which is substantially stress-free over its entire marked area and continuing down through the entire mercury bulb portion, the markings are flush and are in the form of stains that penetrate the surface of the glass shaft.

Although the thermometer itself has had excellent commercial acceptance due to all of the foregoing advantages, there are certain drawbacks attendant upon its previous method of manufacture as disclosed in said third patent. For example, said method required accurate time-temperature controls in both the annealing and the baking cycles in order to secu e sufficiently close repetition of the readings on finished thermome ers. Also, this process required the formation and subsequent optional removal of an expansion chamber (in addition. to another chamber) communicating with the bore and located at a distal end of the thermometer in order to accommodate expansion of mercury during of staining material with previously applied "points" on the thermometer shaft. Another drawback of the aforesaid previously disclosed method is that it necessitated the use of two heat treatments for the thermometer each of which consumed additional time and required additional equipment and labor.

It is an object of my. present invention to provide a method of making a substantially stress-free flush marked mercury glass thermometer having none of the drawbacks above mentioned of the process described in my aforesaid Patent No. 3,172,289.

More speci ically, it is an object of the present invention to provide a method of the character described wherein only, a single heating cycle is practiced which encompasses both the annealing and baking steps and in which the time and temperature, although still necessarily carefully controlled, are not of the same critical nature as they were in the aforesaid process It is another object of rny invention to provide a method of the character described wherein the thermometer may be baked, marked and annealed without the use of the second chamber by utilizing in lieu thereof the conventional calibration chamber.

It is another object of my invention to provide a method of the character described in which it is not necessary for the applied markings to be precisely registered with previously positioned "points" on the thermometer shaft.

It is another object of my invention to provide a method of the character described which will produce thermometers having a more uniform mass appearance and specifically having the scales thereof centered about a common point, e.g., 102°P, intermediate the. ends of the scale, so that when groups of ther appear to be centered at the aforesaid common point, 7 centimeters, for example, from the base of the mercury bulb.

It is another object of my invention to provide a method of the character described which can be practiced with comparatively inexperienced help at a low cost and by mass production techniques.

Other objects of my invention in part will be obvious and in part will be pointed out hereinafter.

My invention accordingly consists in the various series of steps which will be exemplified in the processes hereinafter described and of which the scope of application will be indicated in the appended claims.

In the accompanying drawings, in which are shown devices for carrying out my invention and thermometers at various stages of the processes, FIG. 1 is a top plan view of the unmarked thermometer blank prior to the practice of ray Invention thereon; PIG. 2 is a similar view of said blank after being subjected to a key calibration temperature; PIG. 3 is a simplified view of a constant temperature bath with a thermometer blank located therein; PIG. 1+ is a top plan view of said blank showing the mercury column shaken off into the calibration chamber from above the trap, said column previously having been raised to the key calibration temperature; PIG. is a top plan view of the blank showing the mercury column raised to i°P after being, shaken off at 86°P, said blank having had a low point marking applied thereto; PIG. 6 is a view similar to FIG. 5 but showing the mercury column raised to 106°F and with the blank provided with a markable scale applied thereto that is matched to the mercury column temperature rise characteristic of the blank but is without consideration to the then existing level of the mercury column for any given temperature; PIG. 8 is a sectional view of an apparatus for burning off excess mercury in the mercury column of the blank; PIG. 9 is a top plan view of a thermometer finished by a process of ray invention; and FIG. 10 is a side elevational view of a laser gapping apparatus used in a modified form of my invention to register to a stain applied scale a mercury column having a thermal rise characteristic to which the scale is matched.

In general, I carry out my invention by deviating from conventional mercury glass thermometer manufacturing practices at the point at which the conventional method provides a thermometer blank 10 (see PIG. 1) having a calibrating chamber. Por the purpose of reference such a blank 10 constitutes a glass shaft 12 v/ith a capillary bore II.. At one end of the glass shaft a reservoir bulb 16 is affixed or formed; at the other end of the shaft there is a large calibrating chamber 18 which is of a volumetric capacity exceeding that of the bulb. Conventionally, there is a trap 20 between the bulb and the, proximal end of the bore, said trap having been provided for maximum temperature recordation purposes in the field and constituting a double V with the tips of the V's Joined. Prior to deaeratlon mercury completely fills the bulb l6, the trap 20 and at room temperature, e.g., 6ΰ°Ρ, substantially all of the bore 1J. and optionally extending into the calibrating chamber Id. It will, of coursej be realized that there is more mercury present than will be required in the finished thermometer, and in etched and filled and raised marked emo d b standard methods with the adjacent part of the thermometer shaft.

Attention is called to the fact that in this thermometer blank 10 no detrimental amount of residual air or moisture is present below the top of the mercury column in the bore. The same was transferred into the calibration chamber by any standard deaeration technique, for exa-uple by chilling the thermometer to 35°F, driving the mercury from the bore and chamber through the trap into the bulb to substantially fill the same, the driving typically being performed by centrifuging the thermometer, bulb outward, vibrating the thermometer in upright position to permit the air and gases to rise within the bulb toward the trap and thereafter at successively higher temperatures, but below the lowest temperatureto be read in the finished thermometer, shaking off the mercury from above the trap into the calibrating chamber.

Thus-, in the deaerated glass blank 10 which now is ready for treatment in accordance with my invention and which is at a room temperature of, for example, 72°F, the level of the mercury is somewhat above or below the trap, e.g. mercury fills the bulb and extends into or slightly beyond the trap, the balance being in the calibrating chamber.

Now, in accordance with my invention, I raise the temperature of the thermometer to a certain critical temperature hereinafter referred to as a "key calibration temperature" which is below the lowest temperature to be present on the marked scale of the finished thermometer, but which is high enough to raise the level of the mercury to a key calibration point 22 (FIG.2) above the top of the trap. This key calibration temperature will be several degrees, e.g., 10°F to 15°F, above the highest temperature used during the deaerating process, the latter, for example being It is important to note here that although Invention, whichever key calibration temperature is selected, in this instance, 88°F, the thermometer must be raised exactly and precisely to that temperature for all the thermometers in a given batch being processed, and for this purpose I prefer to use a constant temperature water bath 2I. (FIG. 3)» t e temperature of which is regulated within a small range, for instance, plus or minus 1/50°F, so that closely precise reproduction..of marking subsequently may be effected.

Next, the thermometer is removed from the constant temperature bath and is allowed to cool below the key calibration temperature, for example, to room temperature or below.

The mercury column breaks at the trap in well known fashion.

Thereupon, the remainder of the mercury column within the thermometer above the trap is driven into the calibration chamber.

It may be observed at this point that whenever I speak of driving the mercury in either direction it may be done by shaking the thermometer or far more simply by employing a spinning type centrifuge such as is commonly used in this field. At this stage (see FIG.1) a precisely regulated amount of mercury remains in and below the trap and use is made thereof, as soon will be apparent, for calibration purposes.

I now raise the temperature of the thermometer, as in a constant temperature water bath, to a precise temperature which is within the temperature on the scale to be marked and is adjacent the lower end thereof. A suitable temperature, for instance, is 9 °F plus or minus a small range, for example, l/50°F. The level of the top of the mercury column is observed (see FIG. $) and a marking 26 is applied to the lens of the thermometer shaft corresponding with this level. This marking is referred to as 1 the "low point" marking. The marking is applied by means of a marking paint or ink which is not thermally labile, that is to say, which for baking and annealing that are in the range of about 81+0°P ta 860°P. However, the paint should be capable of being mechanically removed, as by wiping. For this purpose I use, by way of example, aluminum or bronze radiator paint.

Nov/ I raise the temperature, as in a constant temperature water bath, to an exact higher level (see FIG. 6) which is near the top of the scale of the thermometer, for example, 106°F plus or minus a small range, e.g. l/i?0°F, and apply another marking 28 referred to as the "high point" marking to the thermometer lens with the same or a similar marking ink or paint, v/ith the marking corresponding to the top of the column at this time.

It is appropriate to mention here that the application of the high point marking to the thermometer is an optional but not essential step which I find simplifies the use of my method. My method can be effected v/ith quite satisfactory results with said high point marking omitted.

For the purpose of grading the thermometers in accordance v/ith their mercury column temperature rise characteristics for the subsequent application of accurate permanent scale markings which are appropriate to the particular thermometers involved, I now measure the distance between the high and low point markings or* if the high point marking is omitted, between the low point marking and the top of the mercury column at the high point employed, to wit, 106°F, in this particular example. I'he measured thermometers thereupon are classified and segregated into separate groups distinct from one another by variation in the lengths between the two points which are functions of their mercury column temperature rise characteristics. The groups vary from one another, by some arbitrary small increment, for example, 0.02 inches. I have used this increment because it is well within the ability The next step in the practice of my invention is to apply heat stainable markings 30 (see FIG. 7 ) by means o .conventional heat stainable inks such as are used or the stain marking of glass. The heat stainable markings are applied in the form of a conventional thermomoter scale, to wit, constituting a series of transverse graduations which subsequently v/ill indicate degrees and decimal ar s of degrees. A conventional set of heat stainable markings for clinical thermometers starts at 9-° ' for the lower end and has a higher end of either 106°F or 108°F.

It will be recalled that the thermometers have been classified into different groups the high and low points of which fall within locations which do not vary by more than 2/100ths of an inch. For economy and speed of production I apply the heat stainable markings to a large number of thermometers in a given group in succession and use a stencil the length of which between graduations corresponding to the points is between the longest and shortest point markings of thermometers in the group. For example, if a given group has point markings which very between 1.73 inches and 1.75 inches, the markings on the stencil corresponding to said points v/ill have a total length of between 1.73 lnchee and 1.75 inches, preferably, a median length, as for instance, I.7I+ inches. Thus the spacing of the stencil graduations matches the mercury colxmn temperature rise characteristic of the thermometers in the- group. For this purpose I prefer to employ a stencil such as shown in my said Patent No, 3, 172,289 "the length of which is selectively adjustable by stretching.

It will.be observed that I have not said that, nor in practice do I, apply the aforesaid stencil heat stainable markings in any particular relationship to the locations of the upper and lower point markings 26, 28. The reason for this vi 11 become predetermined, i.e. certain, individual graduation 32 of the applied scale of stencil heat stainable graduations be a precise preselected distance 3^+ from the bottom of the mercury bulb.

Best commercial' results are secured where the selected individual graduation 2 is intermediate the top and bottom of the applied scale and l prefer to arbitrarily use the graduation corresponding to 102°F. The preselected distance from this graduation to the bottom of the mercury bulb (the external lowermost point on the thermometer) must be accurate to the order of visual readability of an average observer, for example, about plus or minus /1000th3 to 10/1000ths of an inch. Any greater accuracy is not warranted. A lesser accuracy would affect the aesthetic appearance of a group of such thermometers and would interfere with accuracy of a step later to be described. I m y employ any preselected distance for the aforesaid measurement with-. in the parameters of the method and the thermometer. Thus one I o parameter is that the ¾- graduation should be above the trap by a commercially acceptable distance. A preselected distance which I favor for the location of the 102°P graduation and which 1 find to be highly practical is 7 centimeters for a clinical thermometer, although plus or minus 10% will also give usable results. It- ill be realized that if a longer thermometer is employed, as for veterinarian purposes, a different preselected distance 3^t- ma be utilized. The distance is so selected that the 102° ma.k on a finished thermometer is within the range that the mercury column can be adjusted to be set at this temperature.

Next the entire thermometer is heated and cooled to anneal the full length of the thermometer, inclusive of the reservoir bulb, so that the thermometer is substantially uniformly annealed over its full length including the scale marked portion -beneath the surface of the glass whereby to effect stain marking of the graduations .

Desirably the heating is carried out at a temperature sufficiently high, e.g. in the order of 800°F, to enable annealing and stain marking to be accomplished in a reasonably short span, for example about two hours.

In a typical heating and cooling step, the heat stain-able marked thermometers- are raised from room temperature to 820°F in 30 minutes. They are held at this temperature for two hours which suffices to stress relieve them to a degree that is commercially acceptable. This same heating period will perform the staining operation. The thermometers thereupon are cooled slowly to room temperature, for example at 50 °F Per hour. The baking temperature and the cooling rates are not critical. ,J-'hus said baking temperature can vary betwe.en about 660°P and 60°F, it being understood that for lower temperatures a longer time for stress relief and stain marking is required. Likewise the cooling rate above specified is not critical. In accordance with art practice, it is known, however, that more rapid cooling rates at high temperatures create stresses that often are unacceptable. o The cooling rate may be more rapid, e.g. 100 F per hour, below about 660°P.

The residium left from the heat decomposible stainable material is flushed off the shaft.

At this time the thermometer is annealed and has a stain marked scale of graduations that is matched to the mercury column temperature characteristic of the thermometer but the quantity of mercury present, which due to the heating step now is distributed throughout the bulb, the chamber and the bore, is in excess of the amount required for the column to precisely register with precise registration, i.e. to calibrate the mercury column to the stain marked scale.

To this end I visually compare with either the low or high point 26,. 28 the corresponding temperature graduation of the stained scale marking freshly permanently integrated with the shaft of a given thermometer. The point selected will be either above (higher than) or below the corresponding temperature graduation. The same step is repeated for each thermometer of a batch and the thermometers are segregated into groups having the same differential between the points and the scales. The variations between the groups typically is 0.1°F. I catagorize the groups as ■+ or - degree . roups, .usually from ♦· 3°P to - 3°P in 0.1°P increments, the * sign indicating that . the scale graduation is lower than the corresponding point and vice versa. For instance, referring to FIG. 7 the thermometer there shov/n belongs in the * 1.2°F group. A positive (- ) correction is made in an appropriate amount for each thermometer in a * group and vice versa.

To make a * correction, first a thermometer is shaken down (all the mercury is driven toward the reservoir bulb, as in a centrifuge), the thermometer is chilled and deaerated as above described, the la3t shake off being performed at about room temperature, e.g. 7-.°F. Now the thermometer is placed in a constant temperature bath maintained at a temperatue greater than the key calibration temperature by a number of + degrees F equal to the positive correction. For negative corrections the bath is maintained at a temperature below the key calibration temperature by the number of - degrees F equal to the negative correction. As a matter of convenience, the largest owed b less is increased in small increments of 0.1°F and then by the smallest positive correction and succeedingly larger positive corrections. Typically the bath will start at ,85°F (88° minus 3°) and finish at 91°P (88° Plus 3°).

It will be recalled that the hi^h and low points were determined from a mercury column calibrated in a key calibration bath of 88°P with the excess mercury shaken into the expansion chamber. Thereby when I now shake the excess mercury from the recalibrated thermometer into the calibration chamber, the recalibrated column. should register within - 0.27 with the stained scale of graduations.

Reca libra tl on checking is typically carried out at 102°P with the process being described. In commercial operation it is observed that about 5» of the reregistered thermometers will fall within the aforesaid acceptable registration tolerance. The other $ is split between columns that read too high and columns that read too lo (>0.2°F). These must be readjusted (if too high) or reprocessed (if too low).

Reprocessing involves reobserving the original differential between the point markings and the applied 3cale, and placing the thermometer in a correction category 0.1 or 0.2°F lower than observed.

Readjustment constitutes "bumir¾ off" of the excess mercury in the following manner. The thermometer is threaded through a bore 36 in a hoat block 38» composed for example of aluminum that is maintained by electric heaters I.O at a temperature, e.g. -i50°F, sufficiently high to vaporize mercury under a high vacuum and below the stress range, 660°F, of the glass. The sides and broad surfaces of the heat block may be covered with a heat insulating layer h-2. Moreover, a baffle is interposed between -said adjacent surface of the heat block is closely registered ·· ; with the 102°P graduation on the thermometer scale, assuming that the thermometer was last heated to 102°P for recal ibration checking. Such registration is effected, by a perforated stop plate I.6 against which the tip of the bulb 16 abuts and which is 7 cm. from the adjacent surface of the heat block, this being the dis-. tance from the 102° P scale marking to the tip of the bulb initially set into the thermometer when the heat stainable scale graduations were applied.

A fan 1+8 circulates cool ambient air over the bulb and in the space between the baffle l+Ij. and the perforated plate Ι maintaining the temperature thereat at less than 1G2°P.

It will be recalled that the thermometers being readjusted read too high so that a given thermometer subjected to a temperature of 102°P will have a mercury column level with a scale graduation of a higher degree, say 102.3 (if the residual divergence is ♦ 0.3°P). Hence when the thermometer is placed in the burn off apparatus and left there for a few minutes, say ten minutes, the mercury in the column above the 102°P 3c le graduation will vaporize- and will condense in the° calibration chamber that is exposed above the heat block or immediately below the same in the area of the thermometer which next will be melted, pinched off and discarded.

Finally the upper ena of the thermometer is flame melted below the calibration chamber containing the excess mercury, pinched off and discarded to leave a finished thermometer T (see PIG. 9).

A satisfactory alternate method of recal ibrating the mercury column to the applied stain marked scale graduation is to disregard the high and low point markings or to make them of a mercury .in o the bulb, are deaerated and are placed in a constant temperature bath at the key calibration temperature of 88°F. The mercury above the trap is shaken off (driven) into the calibration chamber and the thermometers are raised to a temperature of 102°F, at which the mercury columns will lie within the stain marked scales. The mercury columns are read against the scales as the number of degrees under or over 102 °P and the thermometers are arranged in groups as described above. For instance a thermometer with a reading of 103.2°P will be placed in a. +1.2°F group. After shaking down, each group of thermometers is placed in a constant temperature bath of the key water temperature — 88°P — plus or minus the correction and the excess above the trap driven off into the calibration chamber which latter is heated, pinched off and discarded, Still another method of recalibrat ing . the mercury column to the applied scale is to use a key water that is at least 3°P lower than the. key calibration temperature, e.g. 8°P lower, (a key water temperature of 80°F), and driving the excess mercury into the calibration chamber. Then the thermometer is raised to 102°P. The reading will in all cases be above 102°P. The thermometers now have the mercury in excess of 102°P removed in the burn off apparatus described above.

Mention should be made of the fact that it is within the scope of my invention to heat and cool the thermometer blank for annealing purposes, but not for stain marking, prior to ascertaining the mercury column temperature rise characteristic of the blank (the degree of movement of the mercury column in the bore as a function of change in temperature of the mercury in the bulb) and thereafter to proceed as described above with the exception that the heating step for staining will only be high enough, e.g. 700°P, to accomplish stain marking. ^.the temperature rise characteristic of a mercury column, (2) applying heat stainable markings to match the characteristic but without deliberate registration of the column and markin s, (3) heating and cooling the thermometer to form stain markings, (I.) matching (registering) the column to the applied markings by removing excess mercury into the cal brating chamber, and finally (5) removing the calibrating chamber with its contained mercury); however this modified method greatly simplifies the first and fourth steps.

Pursuant to the aforesaid modified form, a thermometer blank, previously deaerated, is heated sufficiently, as by boiling, to connect the mercury in the reservoir to the mercury in the calibration chamber as a single continuous mass through the trap and bore. The thermometer is allowed to cool to room temperature, or below, and the iiiercury in the bore and calibration chamber is driven toward the bulb an amount sufficient to fill the void at the top of the bulb left Upon cooling so that a continuous mass is reestabilished . Next the thermometer is warmed in a constant temperature water bath to a predetermined temperature which corresponds to a low scalar marking temperature graduation that subsequently will be applied, say 9l\.°V , Thereupon the mercury column is interrupted (broken, i.e. severed or gapped) a a location which is a predetermined distanoe from the base (bottom) of the reservoir bulb and above the trap, say one and one-half inches (set by placing the bulb against a plate 1+9 that is 1-1/2" below the predetermined location), by applying thereto in a direction transverse to the column a narrow high intensity zone of energy such as light energy or heat energy capable of volatilizing a narrow transverse segment of the column without inducing a high local stress in the 0 (see PIG.10) issuing from a laser source 52. The laser beam has a dimension parallel to the length of the mercury column of about 0.005 inches and, in effect, slices out, by volatilizing, a transverse segment of mercury to leave a space (gap) of this thickness in 'the column. Alternate forms of high intensity narrow zones of energy are those developed by the application of a! high frequency electrostatic field or a high frequency mechanl- ; cally vibrating field.

After the gap is formed in the column, the mercury of| the column above the gap slowly rises to increase the mass of the mercury previously present in the calibration chamber. It i3 to be observed that for this phenomenon to occur the mercury column must be continuous from the gup to the · calibrating chamber. The column of mercury below the gap remains quiescent.

Nov/ the thermometer is placed in a constant temperature bath maintained at a temperature which corresponds to a high scalar marking temperature graduation that subsequently will be applied, say 106°F.

The linear distance between the predetermined location (1-1/2" from the plate U ) and the level of the mercury column after removal of the thermometer from the 106°P bath is ascertained. This distance is a measure of the mercury column temr perature rise characteristic . and, it will be appreciated, has been determined with greater ease than the first steps outlined above for securing a similar type of measurement, 'i'he thermometers are arranged in groups which distinguish from one another in the manner previously described and thereafter have heat stain-able markings applied thereto to match the said characteristics as already detailed at length hereinabove. Preferably the 102°P marking is at the same distance, say 7 o , from the base of the bulb for the thermometers of all the groups. Now the thermo latter being optional as mentioned before.

Next the mercury column is precisely registered to the freshly applied stain marked graduations by a step that is simpler to carry out than the equivalent step recited for the earlier described process. This is accomplished by driving the mercury toward the bulb, deaerating the mercury ana heating the thermometer, to connect the mercury in the column to the mercury in the calibrating chamber so that there is a single continuous mass of mercury from the bulb to the calibrating chamber. , Thereupon the thermometer is coolea to room temperature or below and then shaken down to rejoin the mercury in the column to the mercury in the bulb. At this time there is a single continuous mass of mercury from the bulb to the calibration chamber. Next the thermometer is heated to the temperature at which the corresponding stain marking for thermometers of all groups is at the same distance from the base, in this instance lu2°K, and the column is interrupted (gapped) at this point by. applying thereto a narrow high intensity zone of energy 3uch as immediately above described, e.g. a laser beam.

The mercury in the column above the interruption slowly ascends to swell the mass of the mercury previously present in the calibration chamber. The column below the interruption remains immobile. The thermometer now is complete except for the removal of the calibration chamber containing the excess mercury. It will readily be seen that this last described mercury registration step is far more rapid to accomplish than that previously mentioned since it doe 3 not require reading out differentials and the use of many correction water baths of a multitude of temperatures, or centrifuging. Also the accuracy of the finished thermometer is far greater, in the order of "t 1/20 of a degree P. a narrow high intensity zone of energy to the column so as to split the same and allow the mercury of the column above the split to retract into the mass of mercury in the calibration chamber, in contradistinction to the previously described matching step wherein the excess mercury above the trap is driven into the calibration chamber. In the driving step the mercury, as the thermometer is centrifuged, calibration chamber outerward, tends to flow to the top of the calibration chamber and thereby opens a passageway from the ca illary bore to the gases trapped in the calibration chamber so that gases are present in the bore above the mercury column of a finished thermometer. Upon occasion this causes rejects classified as "retreating indices".

Contrariwise, the splitting technique of the last described mercury matching step never permits a gap to be formed at the seal located at the junction of the bore and the calibration chamber so that the finished thermometer is free of air and water vapor above the mercury column.

It should be understood that the sp litting technique is also useful in the manufacture of commercial mercury thermometers which do not have traps.

It thus v.'ill be seen that I have provided processes . which achieve the several objects of my invention and which are well adapted to meet the conditions of practical use.

As various possible embodiments might be made of the above invention,, and as various changes might be made in the embodiments above set forth, it is to be understood that all matter herein described or shown in the accompanyin drawings, is to be interpreted as illustrative and not in a limiting sense.

Claims (1)

1. 22 A method of stain marking a mercury glass sealed thermometer ascertaining within the range of the markings to be the mercury column temperature rise characteristic of a sealed thermometer blank having no scale markings thereon and composed of a reservoir bulb and a shaft having communicating at one end with the bulb and at the other end with a calibrating the blank containing an excess of characterized by the following further applying to the shaft in the linear area to be a scale of graduations constituting heat stainable materia with the graduations mutually spaced to match the mercury column temperature rise characteristic of the sealed blank and without consideration of precise registration between the actual level of the mercury column for any temperature and the corresponding scale graduation for that then heating and cooling the sealed blank so as to mark the glass shaft with a scale of stained graduations corresponding to the aforesaid then transferring sufficient mercury into the brating chamber to precisely register the actual level of the oolumn of mercury for all temperatures within the range of markings with the scale graduations for those and then removing the calibrating chamber and the mercury A method as set forth in Claim wherein the scale of graduations is applied to the shaft with a certain graduation of the scale that corresponds to a certain temperature located a preselected distance from the tip of the bulb end of the b 23 A method as set Claim wherein a certain graduation is an intermediate scale A method as set forth in Claim wherein heating and cooling the sealed blank anneals the sealed blank over the full length A method as set forth in Claim wherein sealed blank is annealed and marked A method as set forth in Claim wherein the mercury column temperature rise characteristic of the sealed thermometer blank is ascertained by measuring the difference in the heights of the mercury column at two different specific A method as set in Claim wherein height of the mercury column at the lower end of the two specific temperatures is obtained by removing to the calibration chamber at a reference calibration temperaturebelow said lower specific t mperature mercury in excess of a height near the reservoir and then raising the thermometer to said lower specific A method as set forth in Claim 6 for stain marking a sealed clinical thermometer a maximum temperature recording trap above the reservoir bulb wherein the height of the mercury column at the lower of the two specific temperatures ie obtained by raising the temperature of the sealed blank to said lower specific temperature while the mercury forms a continuous mass from the reservoir bulb to the calibration chambers through the trap and bore and then interrupting said column at a point remote from the calibration chamber by applying to said point a narro high intensity zone of energy so as the column and 24 permit the mercury above the gap to rise up to swell the mercury In the calibrating A method as set forth Claim wherein the narrow high intensity of energy is applied by directing a laser beam to A method as set forth in Claim wherein the mercury column is calibrated at a specific reference calibration ture below the lowest temperature to be present on the marked scale of the finished thermometer prior to heating and cooling and wherein t he registration of the mercury column is by ascertaining the temperature differential between the height of the mercury column at said specific reference calibration temperature and the scale graduation of said specific reference and then after heating and cooling registering the mercury column with the scale graduations by removing the calibration chamber sufficient excess mercury to reference calibrate the mercury column at a temperature differing from the specific reference temperature by said temperature A method as set forth Claim wherein mercury is registered the scale graduations after heating and reference calibrating the mercury column to a specific temperature lower than the lowest scale raising the temperature of tne sealed blank to a second temperature ponding to a scale ascertaining the temperature differential between the height of the mercury column at said second temperature and the scale graduation of said second and then removing into the calibration chamber 25 sufficient excess mercury to reference calibrate the meroury column a temperature differing from the specific temperature by said temperature A method as forth in Claim wherein mercury column is registered with the scale graduations by after heating and cooling calibrating the mercur column to a specific temperature lower than the lowest scale raising the temperature of the sealed blank to a second ture corresponding to a specific scale graduation and by burning removing into the calibrating chamber all mercury in the bore above specific scale A method as set forth in 1 for stain marking a sealed clinical thermometer having a maximum temperature recording trap above the reservoir bulb wherein the mercury column is registered with the scale graduations by after heating and cooling forming the mercury into a continuous mass from the reservoir bulb to the calibrating chamber through the trap and heating the sealed blank to a temperature corresponding to a specific scale graduation and then interrupting said column at a point corresponding to said specific scale graduation by applying to said a narrow high intensity zone of energy so as to gap the column and permit the mercury above the gap to rise up to swell the mercury in the calibrating 1 A method set forth in Claim wherein the narrow high intensity zone of energy is applied by directing a laser beam to said A method of marking a mercury thermometer stantially as herein described with reference to Figures to of the accompanying marked by any of the methods claimed any of preceding For the Applicants insufficientOCRQuality