342 



Mr. Grervaise Le Bas on 



An additional test o£ the above rule, under the conditions 

 stated, is furnished by the subjoined table. 





XV. — Table showing 



the validity o£ the Valency Law 



• 



PAV 



8 H 1S 



Ratio a. 



C-H li; 



145-44 

 147-94 



154-58 

 158-68 



Ratio (3. 



C G H U 



Ratio y. 



C 5 H 12 



Ratio d. 



•001474 

 •002949 

 •011795 

 •022411 



165-39 

 168-32 

 175-83 

 180-51. 



1 

 1 

 1 

 1 



0-8794 

 0-8790 

 0-8792 

 0-8791 



0-8792 



0-8800 



-0-0008 



1 27-98 

 133 65 

 137-19 



0-7603 

 0-7601 

 0-7600 



0-7601 

 07600 



-o-oooi 



113-20 

 116-13 



0-6438 

 0-6433 



Mean value 

 Theoretical 

 Error 



s (obs.)... 

 (4:1 rule) 



1 

 1 

 







0-6435 



0-6400 



-0-0035 



It will be noticed that the values of V/W for octane cease 

 to show any difference from those observed for hexane and 

 heptane, so that the deviations only hold under conditions of 

 high vapour-pressure. They are thus a maximum at the 

 critical point. The conclusion to be drawn from the above 

 observation is, that additive relations are best seen at some 

 considerable distance from the critical points. It appears also 

 to be probable that the divergences from the additive rule 

 which doubtless obtain at the critical point (for compounds 

 more complex than octane) disappear when the vapour-pres- 

 sures become relatively small. The very strict observance of 

 the additive rule, made by the liquid volumes of the complex 

 hydrocarbons, at the melting-point and above it, shows that 

 the above conclusion is true. While the law of additivity 

 holds within narrow limits for the hydrocarbons under con- 

 ditions of corresponding pressure, Young has demonstrated 

 the approximate validity of the law of corresponding states 

 for the liquid volumes of the paraffin hydrocarbons under 

 similar conditions (Trans. Chem. Soc. 1900, lxxvii. p. 1142). 



Nevertheless, his calculated values of V/V K , V, and V K 

 being the observed molecular volumes, and the critical mole- 

 cular volume respectively, under conditions of reduced pres- 

 sure, for the four normal hydrocarbons above mentioned, are 

 not nearly so constant as the values of V/W (see following- 

 table). 



The reason is to be found in the imperfection of the standard 

 of reference, viz., V K . The constitutive differences which 

 appear among the paraffins at about the critical point, attain 

 a maximum at that point. They, however, disappear for 

 hexane, heptane, and octane at about the equal reduced pres- 

 sure '04232. It follows, therefore, that when the volumes 

 under identically reduced pressures are compared with the 



