84 M. B. Wiedemann ow Me Specific Heats of Gases. 



up in stirring. The warming-vessel and calorimeter are con- 

 nected tooether by means of a cork, as was done by Regnault 

 in his apparatus. 



In order to maintain a constant temperature around the 

 calorimeter during an experiment, the calorimeter is placed in 

 a cylindrical vessel of sheet brass having two walls ; the height 

 of this vessel is 17^ centims., and the diameter 14J centims. 

 A funnel-shaped orifice in the front part of this vessel allows 

 of the introduction of the tube /? without contact between the 

 two. By means of the side tubes water, maintained at uniform 

 temperature, is allowed to circulate through this vessel. A 

 wooden partition covered with tinfoil, 2, and furnished with a 

 circular opening in the centre, protects the vessel just described 

 from the heat radiated from the warming-apparatus. The 

 calorimeter is supported in a wicker stand in the centre of 

 the brass vessel %. A board covered with tinfoil is placed on 

 the top of ^ ; and to this board another, protected in the same 

 manner, is vertically attached. 



The latter carries a pulley, over which passes the cord 

 attached to the stirrer of the calorimeter ; the stirrer is moved 

 upwards and downwards 40 to 50 times per minute. 



The thermometer of the calorimeter is illuminated from 

 behind by means of a gas-lamp, the heat-rays from which are 

 cut off by the interposition of four glass plates. Immediately 

 behind the thermometer is placed a glass plate covered, with 

 the exception of a space equal to the breadth of the thermo- 

 meter, with tinfoil ; by means of this arrangement foreign 

 light is cut off. 



The thermometer employed was graduated to tenths of a 

 degree ; by using a telescope it could be read to hundredths 

 of a degree. This thermometer was calibrated and carefully 

 compared with a standard from 0° to 40°. 



On account of the size of the apparatus and the great pres- 

 sures required, Regnault's method of storing and delivering 

 the gases, and of measuring their volumes, could not be em- 

 ployed. It was, however, found possible to modify the 

 method of Delaroche and Berard so as to obtain exact results. 

 These experimenters forced the gases from moist animal 

 bladders, which were placed in a balloon communicating with 

 another into which water issued at a constant velocity. From 

 the quantity of water entering, the quantity of gas issuing 

 could be be calculated. By replacing the animal membrane 

 by caoutchouc, the gases could be maintained free from 

 moisture. 



The apparatus which I employ has the following disposi- 

 tion : — A large glass balloon (C) is closed uir-tight by means 



