On the Method of Condensation in Calorimetry. 359 



Some diversity of result exists among the determinations by other 

 experimenters. Probably much of this diversity is to be ascribed to 

 actual difference in the molecular condition of the samples operated 

 on. The veracity of the present method must be judged then by 

 general agreement with previous observations. In the case of zinc, 

 however, the most reliable observations are probably those of Bede, 

 Bunsen, and Regnault. The first of these observers, it will be re- 

 membered, extended his observations to the variations in the specific 

 heat of zinc with change of temperature limit.* From those observa- 

 tions the value for the mean calorific capacity between 10° and 100° is 

 deduced as 0-09412. This is identical, it may be said, with the value 

 found by the method of condensation. 



Compare, also, in this list of experiments on zinc — and throughout 

 the table — the variations of temperature interval, sufficiently revealed 

 in the varying values of t^, with the delicate compensating variations 

 in the weights of condensed vapour, resulting in the close agreement 

 of the values deduced. It will be seen too that among the five results 

 on zinc the extreme variation from the mean amounts to no more 

 than 0*17 per cent. 



The experiments on aluminium, silver, and platinum tax more 

 severely the consistency of the experiments, owing to the limits of 

 accuracy imposed by the balance. Of the experiments made on 

 aluminium, one is not recorded owing to a doubt about the accuracy 

 of the initial temperature coupled with an abnormal result. The 

 mean finally arrived at agrees with Mallet's experimentsf effected in 

 Bunsen's ice calorimeter. This value accords better with Dulong and 

 Petit's generalisation than the lower values of Regnault and Kopp. 



In the experiments on silver, much care had to be taken in esti- 

 mating the value of w. No bucket was used, the specimen being 

 looped in a fine platinum wire, the small quantity of water precipi- 

 tated adhering to its surface. It is the smallest condensation I have 

 attempted to deal with. 



The series on platinum were some of the earliest effected by the 

 method, and that in a very rude form of the apparatus. Two of the 

 first experiments are not included in the list. 



As, I think, some import may fairly be attached to consistency in 

 experiments where prevailing conditions vary, I quote for comparison 

 the extremes of Regnault's experiments on metals I have dealt with. 



Platinum 569 grams 7 experiments. . 0-03223—0-03279 



Zinc 247 „ 3 „ .. 0-09528—0-09589 



Silver 345 „ 5 „ .. 0'05679— 0*05739 



Lead 526 „ 3 „ .. 0-03129— 0-03150 



* ' Mem. Couronnes de l'Acad. de Bruxelles,' vol. 27, 1856. 

 f ' Chemical News,' vol. 46, 1882, p. 178. 



VOL. XLI. 2 B 



