for the Application of the Method of Mixtures. 415 



one of low density, and kerosene, of specific gravity approxi- 

 mately^, was taken. The air-thermometer thus constructed 

 proved very sensitive, and a change in the temperature of 

 the calorimeter-cup of r J^° C. was clearly shown by an 

 elevation of the manometric column. 



The calorimeter-cup A is made in the form of a tube of 

 silver, ^ millimetre in thickness, of the general form of a 

 test-tube, cemented to a rubber stopper which may be inserted 

 air-tight into the thermometer-bulb *. Silver was selected as 

 the material used for the cup on account of its high conduc- 

 tivity for heat, which causes the temperature of the cup to 

 quickly become that of its contents. The lower half of the 

 outer surface of the tube is coated with a thin layer of lamp- 

 black mixed with turpentine and shellac, for the purpose of 

 increasing its radiating power. 



The water-cooler and dropper is supported upon a vertical 

 rod in such a manner that it may be quickly turned about 

 the rod as an axis, and may deliver water directly to the 

 calorimeter-cup. The cooler consists of a copper receiver 

 covered with heavy felt, within which the water-receiver W 

 is placed. A drainage-tube D, provided with a rubber-tube 

 connexion, conducts away the water from the melting ice I 

 with which the receiver is filled. The water-receiver W is 

 made in the form of an inverted cone of tin-plated copper. 

 This form has been found most satisfactory for maintaining 

 the water at constant temperature, as the ice, resting upon the 

 sides of the receiver, cannot melt away from them, leaving 

 an intervening air-space. The water-dropper consists of a 

 syphon, within the longer arm of which a thermometer is 

 introduced, the bulb of which is held very near the small 

 orifice from which the water drops when the stopcock S' is 

 opened. Thus no barrier is interposed at any time between 

 the thermometer-bulb >and the point of delivery of the cold 

 water. The thermometer used is graduated into tenths of a 

 degree Centigrade scale, and hundredths of a degree may 

 readily be estimated. The zero-point of the scale is just above 

 the cover of the ice-receiver, the stem being immersed in cold 

 water nearly up to that point. 



An electric heater is supported upon a second vertical rod, 

 and may be turned about the rod as an axis until the heater 

 H is directly over the calorimeter- cup, allowing the heated 

 body to be transferred directly to the cup. The heater, which 



* This device was first used, but the calorimeter as now made has an 

 air-tight connexion in this part, similar to that used in the calorimeter for 

 the Method of Cooling as usually applied. All errors due to leakage of 

 air at stopper, &c, which might arise at this point, are thus avoided. 



2G2 



