for the Application of the Method of Mixtures. 417 



The silver tube, which forms the calorimeter-cup, is then 

 withdrawn from the bulb of the air-thermometer, pure water 

 at room-temperature is introduced in sufficient quantity to 

 cover the metal used, and the whole is carefully weighed, 

 The cup is then placed in position in the bulb of the air- 

 thermometer, the stopcock S being opened while the rubber 

 stopper is pressed firmly into place to insure an air-tight joint. 

 Any " crawling " of the rubber stopper is easily detected by 

 closing the stopcock S, and observing whether the mano- 

 metric column remains stationary. A few moments are 

 allowed for this observation in each experiment. Any varia- 

 tion in the temperature of the cup is also readily detected in 

 this observation. In each observation the manometric column 

 has been found to remain stationary after a very short time. 



The initial temperature of the calorimeter-cup, which 

 remains at room-temperature, is then taken by means of a 

 thermometer suspended within the cup having its bulb in 

 contact with the side of the cup, but not touching the water. 

 This is found to remain practically constant throughout a 

 series of observations, agreeing with the temperature of the 

 water in the jar. The thermometer used is graduated into 

 twentieths of a degree Centigrade scale, and hundredths of a 

 degree may readily be estimated. 



Water is allowed to drop from the water-dropper, and its 

 thermometer read as soon as its temperature becomes constant. 

 This occurs after a few T drops have fallen. The manometric 

 column is then brought to the same level L in each arm of 

 the U-tube, by opening the stopcock S. A strip of white 

 cardboard attached to the U-tube, with a horizontal ink-line at 

 the back of the level surface of the manometric liquid, renders 

 the position of the liquid column plainly visible. The stop- 

 cock is then closed, the heater turned around into position, 

 and the heated metal quickly introduced into the cup. The 

 heater is then turned back and the water-dropper quickly 

 turned into position and water allowed to drop into the cup, 

 at first rapidly, then more slowly until the manometric column 

 remains at its original position, indicating that the initial 

 temperature of the cup has been maintained. For several 

 moments the manometric column is then observed, in order 

 to make sure that the heated body has acquired the exact 

 temperature of the cup. In the case of a body of poor con- 

 ductivity the cold water is more slowly introduced, as the 

 heat from the body is more slowly transmitted to the water. 



The specific heat of substances of poor conductivity may 

 thus be obtained with great exactness ; the mixture being 

 practically at room-temperature, radiation loss is inappreciable 

 during the time spent in observing the manometric column, 



