38 Mr. P. J. Hartog and Dr. J. A. Harker on 



Excluding the numbers obtained by Berthelot, which we 

 propose to consider immediately, it will be seen that no 

 results have been published which can be regarded as a 

 serious confirmation of those obtained by Regnault. 



Regnault's experiments, however, were carried out on so 

 large a scale, and with such elaborate precautions, and were 

 moreover so numerous and concordant, that no one has 

 since thought of calling them in question. The experiments 

 of Berthelot quoted above were made, not to determine afresh, 

 the latent heat of steam, but to verify by a comparison of 

 his calculated results with Regnault's numbers, the validity 

 of the assumptions made by him in using an admirably 

 ingenious and simple apparatus, which he had devised for the 

 purpose of determining the latent heat of vaporization of 

 other liquids. Three years ago, on wishing to employ this 

 apparatus, it appeared to the authors that an accurate 

 calculation of the latent heat from the experimental results 

 yielded by its use was a matter of extreme difficulty. In 

 order to elucidate this point, it will be necessary to describe 

 briefly the method of using M. Berthelot's apparatus, and 

 to discuss in some detail the calculation of results from 

 experiments of this kind. 



In M. Berthelot's instrument (Cf. Mecanique Chimique, 

 Vol. I. p. 288 et seq.), the boiler containing the liquid under 

 examination consists of a glass flask, of which the neck is 

 sealed up, the steam passing from its upper part vertically 

 downwards, by means of a central tube sealed through the 

 bottom, into the condensing worm. The condensing worm is 

 fitted to the central tube by means of a ground joint, and 

 is placed in a calorimeter immediately below the boiler. 

 There is thus free communication throughout the experiment 

 between the boiler and the condenser. The source of heat 

 is a small ring-burner placed under the flask and over the 

 calorimeter. The latter is protected as far as possible from 

 radiation by means of suitable screens. 



