US285676A - Electrical thermostat - Google Patents

Description

(No Model.)

EH. PRENTISS' t J. A. TILDEN.

ELECTRICAL THERMOSTAT.

No. 285,676. Patented Sept. 25, 1883.

Vlg E Figa lx:

n, virus. mow-umm. www. uc.

UNITED STATES P IATTENT EEIcEa FREDERICK H. PEENTISS, OE DOST N, AND JAMES A. TTLDEN, OE HYDE PARK, ASSIGNOES TO THE AUTOMATIC ETRE ALARM ASSOCIATION, OE BOSTON,

MASS A OHUSETTS.

ELECTRICAL THERMOSTAT.

SPECIFICATION forming part of'Letters Patent No. 285,675, dated September 25, 1883.

Application tiled December 7', 1532.

(No model.)

To all 'whom t may oon/eerie:

Be it known that we, FREDERICK Hfnnrr rriss and Janus A. TILDEN, citizens of the United States, residing, respectively, at llos ton, in the county of Suffolk and State ol" Massachusetts, and at Hyde Park, in the county of Norfolk and State oi Massachusetts, have invented a new and useful Electrical Thermostat, oi' which the following is a specitication.

Our invention relates to improvements in electrical thermostats in which an electric circuit is made or broken by the movement of a movable electrical conductor, which conduct or is moved at a predetermined temperature by the vaporization oi' a volatile liquid contained in a suitable reservoir, which temperature is determined by the properties ol" the saturated vapor of the volatile liquid used; and the objects of our invention are to make or break an electric circuit whenever the teniperature of the atmosphere surrounding the thermostat reaches the degree at which the contained volatile liquid vaporizes. XVe attain these objects by a device, modifications oi which are illustrated in the accompanying drawings, in which- Figure l is a vertical section oi' an electrical thermostat embodying our invention as used on an open circuit. Fig. 2 is a vertical section of an electrical thermostat, also em bodying our invent-ion, as used on a closed circuit. 1

The tube a is shown iilled with mercury between the points j' and g. The upper end ot' the tube is sealed by fusing in a lampor blowpipe iiaine, and contains a volatile liquid, which completely fills the upper part ot' the tube above f. The receiver or holder b consists of a tube of glass or other suitable substance, the Jlower end of which is fitted with a rubber cork, d, or other non-conducting material, hollowed out, as shown, and through which pass two wires, E and E. The tube A passes through a stopper, c, of cork, papiermache, or other material, which fits (though not air-tight) the upper part of the receiver b.

The operation of the instrument is as follows: Upon the application of heat the eXpansion of the mercury and of the volatile liquid, as liquids, causes the mercury to rise above the point g, but not so much as to cause any ot" the mercury to be i'orccd out ol' the tube o, into the receiver Z); and we do not claim any movement of ihe mercury produced by such expansion. Vhen, however, upon the i'urther application of heat, the boiling-point ot the volatile liquid is reached and the forniation oi' vapor ensues, the mercury will be forced out rapidly and instantly into the receiver b, and thus close the circuit by forming an electrical connection between the wires or electrodes E and E. Thus, in case sulphuric ether were chosen as the volatile iluid, the boiling-point of which is about 9So Fahrenheit, 6 5 the circuit would be closed at that temperature. Bisulphide of carbon, the boiling-point of which is about 11SO Fahrenheit, would close the circuit at 118 Fahrenheit, and so, also, alcohol at 1720 and water at 212. Other temperatures may be readily obtained by the use oi' other liquids, among which are the long list of hydrocarbons.

Turning now to our second modihcation, (shown in 2,) -the bent tube of glass is shown iilled with mercury between the points i' and s on one side and between the points t and a on the other side, while the volatile liquid completely iills the tube between the points s and t. The two electric wires 'L' and 'if' are introduced, as shown, and terminate, rcspectively, fi below the ineniscus T and Il below the meniscus u, the mercury between tand Y u thus forming the electrical connection. The operation is as follows: Vhen, upon the application oi hea-t, the boiling-point of the vola tile iluid is reached, the mercury is depressed in the two legs O and l? and rises in the two legs K and N, and in consequence of the leg N being shorter than the leg K the mercury ovcr- 9o flows from the leg N, exposing the end of the wire i, thus breaking the circuit.

Other forms can be used, both for open and closed circuits, besides these, and we do not confine ourselves to the special forms of the instrument shown in the drawings.

It will be seen from an inspection of the drawings that, since a very small quantity of volatile liquid (much less than here shown) is sufficient to drive out the mercury, no deli- Ico cate proportionment of parts is necessary either oi` the liquids or the glass. It will also be seen that the wires require no accurate adjustment.

Ve are aware that prior to our invention mercury and other liquids have been com- 5 bined in electrical thermostats; but heretofore the circuit has been closed or broken by the eX- pansion ofthe liquids as liquids alone, thereby requiring an apparatus of delicate and expensive construction with ne adjustment of electrodes, thus making the instrument quite too costly for general introduction, while in our instrument the temperature at which the circuit is opened or closed is determined solely by the volatile liquid employed, and the temi 5 perature at which the signal is given will be at the boiling-point of that liquid.- Now, as the vapor is many times the volume ofthe liquid, it is evident from the very considerable movement of the mercury caused thereby that the size of the glass is immaterial, as is also to a great extent the distance of the electrodes, thus greatly simplifying and lessening the cost of construction. To make the action ofthe thermostat clearer, and to show lprecisely the temperature at which the movement of the mercury would be caused by the conversion of the lighter liquid into vapor, -we can take, for example, a thermostat as herein described in which the lighter fluid 3c is water. Now, it is evident that the water would give oil vapor at a temperature when the tension of the vapor would just balance external pressure. At the temperature of 212 Fahrenheit the tension of the saturated vapor of water is equal to 29.92 inches of mercury, and when the atmospheric pressure is also 29.92 inches the tension of the water-vapor is just equal to the atmospheric pressure, and the temperature 212O Fahrenheit isr called the boiling-point, the pressure 29.92 being the average height of barometer at sea-level. lf reference be made to Fig. 1, it will be seen, in order that a vapor may form from the lighter liquid, the tension ofthe vapor must be equal to the dierence between the atmospheric pressure (as indicated by barometer and expressed in inches of mercury) and the vertical distance g f.` For example, if the height of barometer is 29.92 and the mercury column gf is 6.46 5o inches, the actual pressure is 2992-646 or 28.46 inches. N ow, the temperature at which the saturated vapor of water has a tension of 23.46 inches is 200. Fahrenheit, and consequently the temperature at which such a thermostat would act by converting its lighter liquid into vapor would be 200. By making the vertical distance gf 17.17 inches the action would begin at the temperature of 172 Fahrenheit. In the case of another liquid (not water) the action would be similar, and would 6o follow the law of the relation between the temperature and the tension of the saturated vapor of the liquid used.

Having described our invention, what we claim, and desire to secure by Letters Patent, is-

1. In an electrical thermostat, the combination of mercury with a4 volatile liquid of different specific gravity, both contained in a suitable holder and relatively arranged sub- 7o stantially as described, whereby when said volatile liquid becomes a vapor by the application of heat the mercury is suiciently displaced to close or break an electric circuit, as set forth. 7 5

` 2. An opencircuit electrical thermostat, composed of a glass tube closed at one end and open at the other, and containing mercury and a lighter volatile liquid, a holder for said tube, and two electrodes arranged to be electrically connected by mercury displaced from said tube, asset forth.

3. A combination of areservoir containing a `liquid which at a given'pressure volatilizes at a given temperature, to be indicated by making or breaking an electric circuit, and alsov a mobile electrical conductor, ksaid reservoir being sealed on the side intended to contain the Volatile liquid, with two electrodes adapted to be electrically connected or disconnected by the movement of the mobile electrical conductor within 'the reservoir under the increasing tension of the vaporized volatile liquid, substantially as described.y

FREDERICK H.A PREN TISS. JAMES A. TILDEN.

Images