244 Mr. G. J. Parks on Beat Involved or 



conditions, but Mr. Linebarger's methods seem to leave nothing 

 to be desired, and the experiments now to be described were 

 made in a similar way. 



The precipitated silica, sand, or other substance to be 

 experimented upon, was heated in an evaporating dish to dull 

 red-heat. A test-tube was drawn out to a narrow neck at 

 about seven or eight centimetres from the closed end, and the 

 tube was then weighed. Some of the powder was now placed 

 in the tube while it was still hot, and the tube was connected 

 to an air-pump, and the air was exhausted as completely as 

 possible, the powder being at the same time heated until 

 the tube showed signs of softening and closing in under 

 the atmospheric pressure. The bulb was now sealed at the 

 narrow neck, and when cold the whole of the tube and the 

 powder were weighed together ; the difference between this 

 weighing and the first weighing gave the mass of the powder, 

 and a third weighing gave the mass of bulb and powder. 



The calorimeter used in these experiments was a copper 

 vessel, 9 cm. in height and 7*5 cm. in diameter ; it weighed 

 104-605 grammes, and its water equivalent was 9*95 grammes. 

 This was suspended by silken threads inside another co])per 

 vessel, this again was placed in a glass beaker containing water, 

 and the glass beaker was placed inside another glass beaker r 

 the space between the two beakers being filled with "glass 

 wool " or " cotton silicate/' which is a very bad conductor 

 of heat. The whole apparatus was kept in a cupboard with 

 glass doors. The temperature of the calorimeter could there- 

 fore be kept constant for a considerable time. 



The thermometers were divided to *02° C, and the readings 

 were taken to the tenth of a division, so that there was a possible 

 error in each reading of not more than '002° C. 



An instrument was used to serve the purpose of crushing 

 the bulb, thus liberating the powder under the surface of the 

 water, and it also served as a. stirrer to keep the temperature 

 of the water uniform. A piece of brass tubing about an inch 

 in diameter was filed away in the middle, thus leaving two 

 rings at the ends about an inch apart and connected by that 

 part of the tube between them which had not been tiled away. 

 A nut was soldered on to the tube between the rings and a 

 screw worked in the nut, the axis of the screw being at right 

 angles to the axis of the tube, so that when the glass bulb was 

 placed in the tube it was held firmly by the screw pressing 

 against it, and a few more turns of the screw were sufficient 

 to break the bulb. The top of the screw was flattened to a 

 sharp edge, which engaged in a split at the end of a stout 

 brass wire ; this wire could thus be used to turn the screw, 



