The name given to an instrument invented and recently patented by Dr. Ure, for regulating temperature in vaporization, distillation, and other processes, in which the agency of heat is required. It is effected by increasing or diminishing the size of the apertures through which the calorific medium is transmitted. The nature of the contrivance, and its mode of action, will be understood by reference to the annexed diagram.
a b, represent a compound bar, composed of two flat pieces of metal, possessing different powers of expansibility by the same increase of temperature, such as iron and zinc, firmly rivitted together. Now, suppose the most expansible metal, the zinc, placed on the upper side, the compound bar will bend downwards to the position represented at a' b'; and by diminution of the temperature below that at which the metals were rivetted together, a flexure in the contrary direction would take place; and thus a motion is obtained from any change of temperature, which may be made, through the medium of levers, available in checking the cause of change, by altering the size of the opening through which the change was effected. Let c represent a stop-cock, through which steam, hot water, or other fluid enters, to communicate heat to the vessel containing the thermostat a b, and let c d be a lever or handle, by which the cock is turned, joined to the compound bar, by the connecting-rod d b; also, let the plug or the cock be so adjusted, that it shall be partially open when the lever is in the position represented by cd; and less open when in the position represented by c d'; then it is evident, that any increase of temperature, beyond that to which the instrument may have been adjusted, would, by causing the instrument to bend downwards, immediately diminish the passage, and consequently the supply of steam, hot water, or whatever fluid may be used for communicating heat.
While, on the contrary, a diminution in the temperature would cause the bar to bend upwards, and thus increase the passage for the admission of a greater quantity of the heating vapour or fluid.
The patentee gives a variety of examples, of the application of his thermostat for regulating the admission of heating fluids, as well as for regulating the ventilation of rooms, public buildings, etc, some of them displaying considerable ingenuity; but they all depend upon the principle above explained, and therefore we have not deemed it necessary to describe them.