US320749A - Lothian - Google Patents

Description

2 Sheets-Sheet 1.. G. T'. BEIL-BY.

AIR THERMOMETER.

(No Mgdel.)

. Patented June 23,1885.

u. PETERS. mwunmm w. Walhingtnm o. c.

2 Sheets-Sheet 2.

(No Model.)

G. T. BEILBY. AIR THERMOMETER'.

No. 320,749. Patented June 23,1885.

N. PETiflS. Pllokbliihagripher, Wahlnglull, D. C.

UNITED STATES PATENT OFFICE.

GEORGE THOMAS BEILBY, OF MIDOALDER, COUNTY OF MID-LOTHIAN,

SCOTLAND.

AIR-THERMOMETER.

SPECIFIGATION forming part of Letters Patent No. 320,749, dated June 23, 1885.

Application filed June 25, 1884. (No model.)

To all whom it may concern:

Be it known that I, GEORGE THOMAS BEILBY, of Midcalder, in the county of Mid- Lothian, Scotland, Fellow of the Chemical Society and chemical engineer, have invented Improvements in Thermometers, the following being a specification of the invention.

This invention has for its object improvements in instruments for ascertaining the measurements of temperature, especially at points above or below the range of the mercurial thermometer.

The apparatus for carrying out these improvements is represented in the accompanying drawings, in which all the figures thereof are vertical sections.

Figure l is a view of my improved thermometer. Fig. 2 is a View of the same on a smaller scale, in which a pressure-regulator, in the form of a long range or open scale barometer, is connected thereto. Figs. 3 and 4 show modifications.

In the several figures like reference-letters indicate corresponding parts, with the two exceptions in reference to Figs. 3 and 4 hereinafter referred to.

The apparatus consists of several principal parts:

First. The bulb or expanding-vessel a, filled with dry air or other suitable gas.

Secondly. The measuring-tube b, in which the gas to be measured is cut off from the outer air by the piston or indicator 0, of mercury or other suitable material.

Thirdly. The connecting-tube (l, by which the gas passes from the bulb or expandingvessel a to themeasuring-tube b, or vice versa. The cubic capacity of this tube :1 must be inconsiderable as compared with that of the bulb to and measuring-tube b.

Fourthly. The jacket-space e and easing f, inclosing the same and surrounding the measuring tube 1), and through which casing f steam of approximately-constant pressure is passed, or in which any other suitable medium is contained, thus forming a jacket thereof, so that the said measuring-tube b and its contained gas are maintained at a constant known temperature.

Fifthly. An automatic pressure-regulator, in one form of which, as represented at Fig. 2, the free end of the measuring-tube bis connected by means of the tube 9, of small bore and of convenient length, with the tube h, (which is hereinafter called the barometertube,) placed perpendicularly and closed hermetically at its upper end. In this ba rometer-tube h the column 75 of mercury is provided, of sufficient height to give the desired pressure on the gas contained in the measuring-tube b. longer than the column 1) of mercury contained therein, so that changes of volume occurring within the apparatus cause the said column 2' to move up or down in the tube 72. without alteration of its length, and consequently without alteration of pressure.

In place of regulating the pressure of gas contained in the measuring-tube b by the special form of barometric apparatus represented at Fig. 2, it may be regulated by means of the instruments hereinafter more particularly de* scribed with reference to Figs. 3 and 4 of the accompanying drawings; or, in place of an automatic pressure-regulator, an adjustable pressure-regulator may be employed.

The action of the construction of apparatus hereinbefore described is as follows: \Vhen the bulb or expanding-vessel a is heated, the expansion of the contained gas causes a part of the said gas to be expelled through the connecting-tube (1 into the measuring-tube b. The piston or indicator 0, of mercury, is driven forward or upward in the said tube b, and by suitable graduation the volume of the expelled gas is measured by the position of the said piston or indicator 0. The cubic capacity of the connecting-tube (Z being comparatively small, the variations of the volume of the gas contained in it, as influenced by changes of temperature, may be neglected without seriously aiiecting the accuracy of the observations.

The temperature and pressure of the gas in the measuring-tube b are known and constant. The expansion of the material of the bulb a itself can be calculated. It .is therefore pos sible to measure with any required accuracy the expansion of the original gas in the bulb a under the influence of any unknown tem- The barometer-tube h is much perature by measuring the volume of the gas in the measuringtube 1).

Under the system hereinbefore described with reference to Figs. 1 and 2 of the accompanying drawings, the pressure of the gas or air within the instrument is regulated by a special form of apparatus, or is allowed to vary with the atmospheric pressure. By the instrument represented at Fig. 3 an approximately-constant pressure is maintained within the instrument when at Work by continuing the free end of the measuring-tube 1; into the vessel j, of comparatively large capacity. This vessel j is closed to the outer air. It is, like the measuring-tube b, surrounded with the steam-jacket e and easing f, by means of which a constant temperature is maintained. When the ratio of the capacities of the measuringtube 12 and vessel j is known, the appropriate correction for the slightly-varying pressure within the instrument is easily applied to the graduation.

The instrument represented at Fig. 4 is one wherein the pressure vessel or regulator takes the form of a tube, 70, returned alongside of the measuringtube b, with which it is connected at Z, and (as in the instrument represented at Fig. 3) is surrounded with the steam-jacket e and easing f, by means of which a constant temperature is maintained.

By the employment of the pressure vessels or regulators j and 7c in the manner shown at Figs. 3 and 4, the instrument becomes a close thermometer, which, having been once filled with dry air or gas, is not liable to derangement from tarnishing of the inside of the tubes or of the mercury.

The steam inlets and outlets to the steamjackets 0 upon the several instruments represented on the accompanying drawings are respectively marked m and n.

The use of an automatic pressure-regulator such as I have hereinbefore described, of various forms, obviates the necessity for baro- U metric observation such as would be needed if the free end of the measuring-tube b were open to the atmosphere. When, however, a pressure-regulator is not used, it is advisable to have the scale of the thermometer movable, so that its zero-point may be adjusted for the pressure of the atmosphere at the time of observation.

The action of the improved apparatus hereinbefore described depends on the comparatively uniform expansion by heat of perfect gases under uniform pressure.

Hitherto no thermometer has come into ordinary use by which temperatures above the boiling-pointof mercury could be accurately indicated and observed by mere inspection of a movable indicator; but with the improved thermometers constituting this invention temperatures up to and beyond the softening-point of glass can be observed as easily as lower temperatures can now be with a mercury thermometer.

Thermometers constructed according to this invention may be graduated by measuring the capacities of the bulbs a and of the measuring-tubes b, respectively, thereafter marking off on the latter the volume of expelled gas corresponding with. each temperature, using in these calculations the cocfficient for the expansion of the gas at constant pressure.

The expansion of the gas in the bulb a with increasing temperatures causes a decreasing amount to be expelled per degree; therefore the degrees as marked on the measuring-tube b diminish in length toward the higher end of the scale.

Certain fixed points of the scale may be determined by experiment, as in the graduation of mercurial thermometers, the graduation being completed by inter and extra polation.

To facilitate the graduation of thermometers, scales or diagrams showing the ratios of the various parts of the scale are prepared by a well-known geometric method, to which any thermometer can be readily referred, and from which it can be graduated.

It is evident that the apparatus and system hereinbefore described can be applied for the determination of low as well as of high temperatures, and it is further to be seen that the said apparatus may be modified byvarious alterations of outward form and arrangement Without departing from the essential features of the invention.

I claim 1. A thermometer formed with a bulb or expanding-vessel, a measuringtube, and a piston or indicator in the measuring-tube, the bulb or expanding-vessel and the measuringtube, containing dry air or other suitable gas, and the piston or indicator dividing thedry air or other suitable gas in the measuringtube, and cutting off the outer air from the dry air or other suitable gas to be measured.

2. A thermometer formed with a bulb or expanding-vessel, a measuring-tube, a piston or indicator in the measuring-tube, and a tube of small capacity connecting the bulb or expanding-vessel with the measuring-tube, the bulb or expanding-vessel, the measuringtube, and the tube of small diameter containing dry air or other suitable gas, and the piston or indicator cutting off the outer air from the dry air or other suitable gas to be measured.

3. A thermometer formed with a bulb or expanding-vessel, a measuring-tube, a piston or indicator in the measuring-tube, and a casing forming a steam-space around the measuring-tube above and beneath the piston or indicator, the bulb or expanding-vessel, and the measuring-tube containing dry air or other suitable gas, and the piston or indicator cutting off the outer air from the dry air or other suitable gas to be measured.

4. A thermometer formed with a bulb or expanding-vessel, a measuringtube, a piston or indicator in the measuringtube, and an extension to the measuring-tube to provide a pressure-regulator, the bulb or expandingvessel, the measuring-tube, and the extension IIO dicator cutting off the outer gas from the gas to be measured, and the barometer forming an automatic pressure-regulator.

In testimony whereof Ihave signed my name to this specification in the presence of two subscribing witnesses.

GEORGE THOMAS BEILBY.

Witnesses:

ROBERT ADAM GUNN, JOHN 1\/IADDER BUDHOPE, Both of 115 St. Vincent Street, Glasgow.

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