On the Method of Condensation in Calorimetry. 



369 



the temperature it is necessary to provide a cover of nonconducting 

 material — as wood — made in halves, and closing so as to permit the 

 reading of the thermometer. 



When it is desired to carry out the experiment, the forked tube, 

 which is connected with the boiler by 2 or 3 metres of rubber tubing, 

 is separately heated with steam, the valve on the boiler being closed. 

 The thermometer in the calorimeter is then read and withdrawn, the 

 cover removed, and the shield rotated into the position for admitting 

 steam. The steam-pipe is now laid in position; the construction 

 enables this to be done very rapidly and easily. Steam is thus passed 

 directly into the inner chamber at two points, and the inner chamber 

 being very slight condenses but a small quantity of steam, so that 

 the displacement of the air is retarded as little as possible, and is, in 

 fact, with the empty calorimeter almost immediate. On steam flowing 

 out freely at the exit-tube, the valve in the boiler is opened and the 

 calorimeter closed by pressing home the stop in the exit-tube. 



The adjustment of the wire in the orifice is now effected by the 

 screws on the tripod. Effected in this way this is a very easy opera- 

 tion, although the orifice may be hardly 1 mm. in diameter and the 

 wire some 40 cm. long. Balance and calorimeter must, however, be 

 steadily supported. The weighing is now begun, and when it is 

 found that the substance is no longer condensing steam, is finished 

 with the shield in the calorimeter in its position for sheltering the 

 substance from draughts. On this operation being completed, the 

 thermometer for taking U° is inserted in its tubulure, which is now 

 again over one of the orifices in the inner shield and hence admits the 

 thermometer freely into the calorimeter. 



Appendix. 



Corrections for Displacement in Steam. 



(1.) The substance being counterpoised in air is not when immersed 

 in steam — apart from the occurrence of condensation — any longer in 

 equilibrium with the counterpoise, the density of saturated steam at 

 ordinary pressures being different from that of air. The deduction 

 from the apparent weight of condensation on the substance is equi- 

 valent to the volume of the substance multiplied by the difference in 

 the weights of unit volumes of steam and air. By the apparent 

 weight of condensation is meant that deduced on subtracting from the 

 weight added to the counterpoise during an experiment the weight 

 due to condensation on the carrier. Let this apparent weight be w v 



The difference in the weights of unit volumes of steam at 100° and 

 air at 15° is 0*000636, calculated on the absolute densities of dry air 

 and steam according to Regnault. 



