Volumes, and Chemical Characters of Liquids. 421 



This being the case with one of the groups of compounds 

 quoted in Table L, it seems only fair to conclude from the 

 perfect analogy of the others at atmospheric pressure, that the 

 same conclusions might be drawn in their cases also, were 

 experimental data available. Hence, in all probability, 



equality of the ratio -^ in different compounds at equal 



pressure depends on a combination of the following : — 



(1) Similarity of chemical constitution, of a kind akin to 

 that concerned in isomorphism ; (2) equality of critical 

 pressure ; and implies also (3) constancy of the ratios V : V 

 and T : T' at all equal pressures. It is possible that the slight 



y 



deviations from perfect equality of -~ , to which attention has 



been directed, are connected with slight differences of critical 

 pressure. 



Young's work further enables us to study the manner in 



which -Ffrf° r one ana * the same liquid varies with variation of 



pressure. Very interesting curves are obtained by plotting 



the ratios -7p T as ordinates and P, P T , or Tas abscissae. In the 



case of fluorbenzene the first curve shows a descent which is 

 very rapid at first, then gradually slows off till a minimum is 

 reached at about 7000 millirn., then a slow but steadily in- 

 creasing rise, which becomes rapid as the critical point is 

 approached. The actual extreme values are *3559 at 5 millim., 

 •2631 at 7000 millim. (minimum), and -4164 at 33912 millim. 

 (critical). The value at 760 millim., already given, is '2837. 

 The curves for the chloride, bromide, and iodide are perfectly 

 similar as far as they go. Those plotted with V T measured as 

 abscissas are nearly parabolic in form. 



Obviously it would be of considerable interest if we were 

 enabled to compare the curves of the halogen compounds of 

 different radicals with one another and these with the curves 

 for their compounds with oxygen, nitrogen, and elements of 

 other natural groups. We should, then, in all probability 

 attain to a fuller understanding of the relations between 

 boiling-point, molecular volume, and chemical character. 



Melbourne, 12th August, 1890. 



Postscript. — It has been suggested to me by Mr. E. F. J. 

 Love, Lecturer in Natural Philosophy in this University, that 

 the relation discussed in the foregoing Paper, when taken 



