RESEARCHES ON EVAPORATION AND DlSSOCIATrON. 299 



vapour ill contact with the liquid substance, at all tempera- 

 tures below the melting-point of the solid. As the statical 

 method in Regnault's hands appeared to negative the 

 thermodynamical conclusion that the vapour-pressures of 

 liquids and solids were different below the melting-point of 

 the latter, the dynamical method was employed, which is, as 

 a rule, capable of yielding more accurate results than the 

 statical method. 



(3) We next investigated the question regarding the 

 vapour-pressures, or, to use the ordinary term, pressures of 

 dissociation, of dissociable bodies. Do the statical and 

 dynamical methods also give identical results, in measuring 

 the vapour-pressures of dissociable bodies ? To this the 

 answer was, — In some cases they do, iu the majority of cases 

 they do not. 



(4) It was found that our dynamical method of measuring 

 vapour-pressures was ap])licable, with slight modifications, 

 to liquids as well as to solids ; and as our experiments on 

 dissociable bodies had included measurements of the vapour- 

 pressures of acetic acid, a description of the method, along 

 with the results for acetic acid, was i)ublished iu the Trans. 

 Ghem. (S'oc, vol. xlvii., p. 42. 



This was deemed necessary, on account of the contradic- 

 tory results obtained by Eegnault, Landolt, and Wiillner ■ 

 and since Horstmanu's views as regards the relation of acetic 

 acid to ordinary dissociable bodies were based on Landolt's 

 determinations of vapour-pressures, these views were proved 

 to be incorrect. 



(6) A method of obtaining constant known temperatures 

 suggested itself, by using the vapours of liquids boiling 

 under known pressures, these liquids being so chosen that 

 their boiling-points overlapped. This necessitated careful 

 determinations of the vapour-pressures of the following 



