A Mirror Thermometer ALEXANDER P . MARION Queens College, Flushing, New York
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HE apparatus described below was devised to fur- washing under running water the deposit on one side of nlsh a s~mple method by which temperature changes the glass may be rubbed off with a wad of cotton. . The light unit consists of a 50-candlepower, 6-to 8could be demonstrated to a relatively large audience. It can be used, for example, to show the thermal effects volt, Mazda lamp (1183) mounted in a metal can diwhich may occur during the solution process or the heat rectly behind the-lens of a 10-power magnifier. If the legs are removed from one of the tripod magnifying evolved in a neutralization. lenses used in the laboratory, the threaded cdllar which remains can be bolted to the lamp housing, thereby providing a focussing adjustment. The exact separation between the lens and the filament will depend upon the distance from the light unit to the screen but will be approximately one and one-half inches for a screen 20 feet away. It is important to have the filament centered directly.in back of the lens. A transformer capable of supplying between six and eight volts a t about nine amperes is necessary if operation from the 110-volt a. c. lines is desired. A storage battery is an alternative. In operation, the image of the filament is brought to a sharp focus on the wall, or a suitable screen, and the thermometer positioned so the mirror intercepts the light beam. In some cases a more distinct image can be obtained with little loss in intensity if the lens aperture is reduced by an opaque mask placed between the two elements of the lens. The choice of an optical system. was based on a consideration of the chief disadvantage of electrical and mechanical methods: the scale, or dial, or other viewing form is usually small and, consequently, the over-all magnification is low. This is in marked contrast to opBasically the apparatus is an optical lever in which tical methods where the relative intensities of the light the torque needed to rotate the mirror is derived from source and of the room illumination determine the althe bimetallic element in a thermometer. A 50-candle- lowable magnification. For example, the original therpower automobile bead lamp serves as the high inten- mometer scale is approximately six inches long but if this apparatus is used with a screen 20 feet away the prosity light soufce. The first step in assembling the apparatus is to re- jected scale is approximately 250 feet, or about 500 move the glass disc protecting the face of a Weston times as great as the original. Even under such circumall-metal thermometer of suitable range (0 to 100°C.). stances the room need not be darkened for the image Two circular cover glasses, of the type used in mounting of the filament is clearly visible. Since the silvered cover glasses give, in effect, two rebiological specimens for observation under the microscope, are silvered on one side, fastened together with a flecting surfaces back to back, readings are continuous dab of deKhotinsky cement so the silver surfaces are in over the entire range of the thermometer. However, contact, and then cemented to the pointer, care being the intensity of the image falls off as the mirror becomes taken to keep them perpendicular to the plane of the parallel to the light beam so a small zone may exist in which no readings can be taken if the room illumination dial. A satisfactory method for silvering a cover glass is to is sutficiently high. Another advantage of this apparatus is that the acdip the clean disc alternately into an approximately 10 per cent formaldehyde solution and then into an ammo- curacy of the readings is essentially maintained equal to niacal silver nitrate solution which contains a trace of that of the original thermometer for there is practically the undissolved silver oxide precipitate. Then while no mechanical load applied to the system.
