78 SIR WILLIAM RAMSAY 



and also acetic acid the curves were of the usual form and the 

 statical and dynamical methods gave the same (or with ammon- 

 ium chloride nearly the same) results. With aldehyde ammonia 

 both curves were of the usual form, but were quite distinct, the 

 temperatures being much higher on the volatilising point 

 curve. For the other substances the volatilising point curves 

 and in some cases the vapour pressure curves were quite 

 different in form, in fact with the chloral compounds and am- 

 monium carbamate there was no simple relation between volati- 

 lising point and pressure. A possible explanation of the peculiar 

 form of some of the vapour pressure curves was given, and it 

 was pointed out that the dissociating substances might be divided 

 into two classes : (a) that including such substances as chloral 

 hydrate, in which there is deep-seated chemical change on dis- 

 sociation, and (b) that including nitrogen peroxide and acetic 

 acid and, possibly, ammonium chloride, in which the chemical 

 change is much simpler 



Our researches on vapour pressures, volatilising points and 

 boiling points included also an investigation of bromine, iodine 

 and iodine monochloride. [Trans. Chem. Soc. 49, 453 (1886).] 



A separate paper [Trans. Chem. Soc. 49, 685 (1886)] contained 

 an account of determinations of the vapour densities of chloral 

 ethyl-alcoholate at a series of temperatures and pressures. For 

 this purpose a Hofmann's apparatus was modified in such a 

 manner that pressure, volume and temperature could all be 

 altered at will. The apparatus is described in the Phil. Trans. 

 178, 57 (1887). We were also led into a controversy with Kahl- 

 baum, who contended that the statical and dynamical methods 

 of determining vapour pressure gave different results. [Berichte, 

 1885, 2855 ; 1886, 69 and 2107.] 



Ramsay had already made determinations of the vapour 

 pressures, specific volumes and critical constants of benzene 

 and ether, a copper block being used for heating the substance. 

 [Proc. Roy. Soc. 31, 194 (1880).] Ramsay arrived at the con- 



