THERMOSTAT, is the name of an apparatus for regulating temperature, in vaporization, distillation, heating baths or hothouses, arid ventilating apartments, &c.; for which I obtained a patent in the year 1831. It operates upon the physical principle, that when two thin metallic bars of different expansibilities are riveted or soldered facewise together, any change of temperature in them will cause a sensible movement of flexure in the compound bar, to one side or other; which movement may be made to operate, by the intervention of levers, &c., in any desired degree, upon valves, stopcocks, stove-registers, air-ventilators, &c.; so as to regulate the temperature of the media in which the said compound bars are placed. Two long rulers, one of steel, and one of hard hammered brass, riveted together, answer very well; the object being not simply to indicate, but to control or modify temperature. The following diagrams will illustrate a few out of the numerous applications of this instrument:—
[Fig. 1130.] a, b, is a single thermostatic bar, consisting of two or more bars or rulers of differently expansible solids (of which, in certain cases, wood may be one): these bars or rulers are firmly riveted or soldered together, face to face. One end of the compound bar is fixed by bolts at a, to the interior of the containing cistern, boiler, or apartment, a, l, m, b, whereof the temperature has to be regulated, and the other end of the compound bar at b, is left free to move down towards c, by the flexure which will take place when its temperature is raised.
The end b, is connected by a link, b, d, with a lever d, e, which is moved by the flexure into the dotted position b, g, causing the turning-valve, air-ventilator, or register, o, n, to revolve with a corresponding angular motion, whereby the lever will raise the equipoised slide-damper k, i, which is suspended by a link from the end e, of the lever e, d, into the position k, h. Thus a hothouse or a water-bath may have its temperature regulated by the contemporaneous admission of warm, and discharge of cold air, or water.
[Fig. 1131.] a, b, c, is a thermostatic hoop, immersed horizontally beneath the surface of the water-bath of a still. The hoop is fixed at a, and the two ends b, c, are connected by two links b d, c d, with a straight sliding rod d, h, to which the hoop will give an endwise motion, when its temperature is altered; e; is an adjusting screw-nut on the rod d, h, for setting the lever f, g, which is fixed on the axis of the turning-valve or cock f; at any desired position, so that the valve may be opened or shut at any desired temperature, corresponding to the widening of the points b, c, and the consentaneous retraction of the point d, towards the circumference a, b, c, of the hoop. g, h, is an arc graduated by a thermometer, after the screw-piece e has been adjusted. Through a hole at h, the guide-rod passes. i, is the cold-water cistern; i, f, k, the pipe to admit cold water; l, the overflow pipe, at which the excess of hot water runs off.
