Evaporation and Dissociation. 

 Table IX. 



209 



Volumes. 



-12°-6. 

 mm. 



0°. 



49°-7. 



73°-7. 



99°-8. 



129°-9. 



151°-4. 



c. c. 



mm. 



mm. 



mm. 



mm. 



mm. 



mm. 



16000 







26-3 





30-0 



345 





8000 





30-7 



50-8 



56-5 



61-2 



68-8 





4000 





58-5 



96-2 



112-5 



121-2 



136-0 



146-3 



2000 



97-0 



110-0 



183-7 



220-0 



2410 



271-3 



2940 



1000 





204-2 



353-0 



422-5 



473-5 



540-0 



573-5 



On comparing the results for acetic acid and for nitric 

 peroxide with those for methyl and ethyl alcohols, ether, and 

 carbonic anhydride, the most noticeable feature is that the 

 isochoric lines are not straight. If it is true that the limiting 

 formulae for acetic acid and for nitric peroxide are, respectively, 

 C 2 H 4 2 and C 4 H 8 4 , and N0 2 and N 2 4 *, then, on the sup- 

 position that the lower formula? remain correct, and that the 

 density remains constant, it is possible to calculate pressures 

 and temperatures corresponding to given isochoric lines ; 

 these lines would be those of a perfect gas, straight, and 

 radiating from absolute zero of temperature and pressure ; 

 and the isochoric line corresponding to a volume v of the 

 simpler molecule C 2 H 4 2 , or N0 2 , will be the same as 

 the isochoric line for the formula C 4 H 8 4 or N 2 4 , and the 

 volume 2v. Now as the density of the more complex mole- 

 cule diminishes with rise of temperature and pressure, it is to 

 be expected that the isochoric line should lie between these 

 lines, and that it should coincide at high temperatures with 

 the isochoric line v, and at low temperatures with the line %v. 



This will be readily understood on reference to the accom- 

 panying plates. Plate III. represents isochoric lines for acetic 

 acid, and Plate IV. for nitric peroxide. Take the volume 

 2000 cub. centims. per gram. The line AB represents the 

 relations of temperature to pressure on the assumption that 

 the formula of acetic acid is C 2 H 4 2 , and its corresponding 

 density 30. The line EF represents similar relations on the 

 assumption that the formula is C 4 H 8 4 , and the density 60. 

 This line, it will be seen, also corresponds to a volume of 

 4000 cub. centims. of gas of density 30. The line CD repre- 

 sents the observed relations of temperature to pressure for 

 acetic acid when the volume is 2000 cub. centims. per gram. 

 It is a curve of double flexure, which, if produced towards B, 

 apparently might touch and become continuous with the line 

 AB ; and if produced towards E might coincide with the line 



* We must here direct attention to an arithmetical mistake in our 

 former paper, " On the Nature of Liquids " (Phil. Mag. Feb. 1887, p. 137). 

 The density of nitric peroxide at — 12 0, 6 is stated to be 52 - 54, it should be 

 42*54 ; and the deductions from that erroneous statement must therefore 

 be withdrawn. 



Phil. Mag. S. 5. Vol. 24. No. 147. Aug. 1887, P 



