1886.] On the Method of Condensation in Calorimetry. 249 



a considerable range of temperature. Two forms of the apparatus 

 employed are described. The calorimeter consists essentially of a 

 vessel of thin metal in which the substance is suspended by a fine 

 wire, the wire issuing through an aperture in the top of the vessel and 

 reaching up to one arm of a balance. The vessel is so constructed 

 that steam can be passed through it from a small boiler, displacing 

 the air around the substance. The substance rests on a light carrier 

 of platinum wire provided with a little catchwater beneath to receive 

 the drops of condensed water. 



The manipulation involved is very simple. The substance being 

 placed on the carrier which depends from the balance, is counterpoised. 

 The calorimeter is then closed around it, the suspending wire passing 

 freely through the aperture provided. This aperture is formed in an 

 absorptive material (plaster of Paris), which ensures that it remains 

 free of precipitated water. A thermometer reading to y 1 ^- degree G. 

 is inserted in the calorimeter, and allowed to remain with the substance 

 for an interval sufficient to secure close equilibrium of temperature. 

 The thermometer being read is removed, and the calorimeter suddenly 

 placed in connexion with the boiler, which supplies a brisk current 

 of steam and fills it immediately. It then remains to note the incre- 

 ment of weight when the substance has finally attained the tempera- 

 ture of the vapour. This stage is revealed in the persistent equilibrium 

 of the balance. t% is observed directly by a thermometer inserted in 

 the boiler, or deduced by noting the height of the barometer and 

 seeking the corresponding temperature of saturated steam from 

 Regnault's tables. A correction is applied to the weight observed in 

 experiment, necessitated by the difference of the weights of the dis- 

 placement of the substance in air and in steam. In accurate experi- 

 ments the value of \ is corrected according to Regnault's formula for 

 its true value at t% . 



The method is convenient for the reasons that it involves no 

 preparations as in Bunsen's change of state method, no delicate 

 thermometry, and the calorimeter being roomy permits of bodies of 

 various shapes and bulks being dealt with. The apparatus, too, is of 

 a simple and durable nature. 



The experiments quoted in support of the method are (1) on the 

 metallic elements, zinc, silver, lead, platinum, and aluminium. The 

 results are in accord with those of Regnault, Bede, Mallett, &c. The 

 degree of consistency between the experiments is greater than that 

 attained in Regnault's researches. (2) On pure water sealed in thin 

 glass bulbs. The results agree closely with the values deduced from 

 Regnault's formula. (3) On mineral substances in various states of 

 aggregation. It appears from these that the result is but little 

 influenced by the extent of surface exposed to the steam. 



The accuracy displayed by the method is explained on the probable 



S 2 



