82 



Mr. J. J. Waterston on certain Thermomolecular 



reference to the absolute increment of volume, not to the relative 

 increment, as I had at first deduced from my own observations 

 in sealed tubes at high temperatures. 



§ 2. This was a fortunate discovery, because, on extending 

 the inquiry to the numerous chemically pure liquids experimented 

 upon by M. Pierre*, other relations make their appearance that 

 confirm the general law, and further develope an interesting con- 

 nexion between molecular volume, liquid cohesion, and saturated 

 vapour-density, which we are enabled to trace distinctly by means 

 of M. Regnault's great and admirable labours published in the 

 twenty-first and twenty- sixth volumes of the Memoirs of the 

 French Academy. 



§ 3. Although a good deal of labour is required to bring out 

 the numerical results from the observations, the thermomolecular 

 relations are simple enough in their nature. I will endeavour to 

 explain them concisely by diagram before proceeding to give the 

 evidence upon which they are founded, and for simplicity will 

 confine the attention to two liquids chemically analogous, — the 

 hydrobromic and hydriodic ethers. 



In fig. 1 the lines wABG, nab &', that represent both the 

 saturated-vapour density and the liquid expansion of these bodies, 



are obtained from M. Regnault^s observations of pressure under 

 the boiling-point (those taken by the dynamic method are pre- 

 ferred). A temperatare t, reckoned from —274°, the zero of 

 gaseous tension, is represented by s S, and S A is the sixth root 



* Annates de Chimie et de Physique, vols. xv. ; xix., xx., xxi., xxxi. 



