EXPEEIMENTAL KNOWLEDGE OF THE TBOPERTIES OF MATTER. 513 



remainder. Ramsay and Young devised a method for constructing the 

 horizontal line (line of equal pressures on Andrews' diagram correspond- 

 ing to the vapour- pressure for any temperature), and obtained these lines 

 for the various isothermal lines so accurately dividing the volumes into 

 equal parts that it was found that the vapour-pressures thus indicated 

 agreed with those of experiment within 1 per cent. This is a remarkable 

 confirmation of the accuracy with which p=:hT — a represents lines of 

 equal volume. 



Similar results were obtained for CO2, and for methyl alcohol and 

 ethyl alcohol ; and the equation p=:bT — a was confirmed as a remarkably 

 accurate representation of the lines of equal volume for these bodies in the 

 gas-liquid state. 



For acetic acid and for nitric peroxide the isochoric lines were not 

 straight, but were curved in such a way that points on them for high 

 temperatures were on nearly straight lines, which woald be isochors for 

 the formulse C.2H4O2 and NO2, supposing that compounds with these 

 formulae in the gas-liquid state behaved as alcohol and ether do ; it is 

 noticeable that in the gaseous state acetic acid and nitric peroxide do not 

 attain constant vapour-densities till they have been heated considerably 

 above their boiling-points. It must be observed, however, that this is a 

 matter of degree ; and so far as acetic acid is concerned, there is as yet 

 hardly sufiicient I'eason for supposing that acetic acid forms a true polymer. 

 The case of nitric peroxide is, perhaps, a case of polymerism in which we 

 have two distinct chemical substances, NO2 and N2O4 '• there are, in fact, 

 distinct physical difierences between nitric peroxide at a low and a high 

 temperature. 



On the Nature of Liquids. 



In a paper on this subject^ Ramsay and Young bring forwai-d a 

 number of considerations from researches of their own,'^ among which is 

 a series of determinations of densities of the saturated vapours of alcohol 

 and acetic acid ; in both these cases the vapour-density, at high tem- 

 peratures, becomes abnormally great : thus, for alcohol at temperature 

 about 250° the pressure is 32,000 mms., and the vapour-density of 

 the saturated vapour 45, the normal being 24 from the formula ; for 

 acetic acid at 250" and 15,000 mms. the saturated vapour-density is 55. 

 But there is this difference between the two cases : the vapour-density- 

 at saturation diminishes continually with alcohol till it becomes normal, 

 ■i.e., 24 at about 20° — similar results to these were got for ether. The 

 case of acetic acid is quite different ; for, although at temperatures above 

 150° the saturated vapour-density continually increases with rise of tem- 

 perature, and this vapour-density sinks as temperature falls to 150°, yet, 

 as the temperature falls below 150°, the vapour-density begins to increase 

 again, till at 20° it is the same as at about 270° ; nor does it become 

 normal, although at 20° the pressure is only a few millimetres, and the 

 vapour-density 59 nearly corresponds to 60 for (0211402)2; but the 

 nature of the curve of vapour- densities of acetic acid at saturation does 

 not suggest a limit at this point. 



Ramsay and Young argue thus with respect to acetic acid : High 

 temperatures are favourable to chemical decomposition, or dissociation of 

 complex molecules ; and we therefore have no reason for assigning to 



• Phil. Mag. Feb. 1887. « Phil. Tram. 188(5, Part I. 



1888. L L 



