22 MOLECULAR WEIGHT AND POLYMERISM 



kilogram as before, the molecular weight M as obtained 

 from the vapour density. Then 



.dP MqdT .- 2T 2 dP 

 AVP = *T, so that - = -- or M= 



Introducing the values 



P 10 = 6-6 mm., P 20 = n-6 mm., q = 85 cal., 



we have 



.... 2X288 2 x<5 



M = 7T = J07 



85 xg-i xio 



instead of 60 ( = C 2 H 4 2 ),in accordance with the conclusion 

 from direct vapour density measurements, that saturated 

 vapour of acetic acid has a nearly double molecular weight, 

 and consists mainly of double molecules. 



C. Results. 

 i. Connexion with the Atomistic Hypothesis. 



The fundamental scientific interest of the results 

 obtained by application of Avogadro's law lies in the 

 complete connexion that can be established between the 

 chemically determined atomic weights and the molecular 

 weights arrived at physically. 



The necessary conclusion from atomistic reasoning, that 

 in reactions the molecules concerned must be in whole 

 number relationship, as e. g. when methane (CH 4 ) is burnt 

 in nitrous oxide (N 2 O) 



CH 4 + 4 N 2 = C0 2 + aH 2 + 4N 2 , 



agrees with Gay-Lussac's law that in reactions the volumes 

 of gases concerned are in such a relationship. According 

 to Avogadro the ratios in question may be read off the 

 equation directly, in the form of the coefficients occurring 

 in it, as each molecular symbol corresponds to the same 

 volume, so that 



Vol. CH 4 : Vol. N 2 : Vol. C0 2 : Vol. H 2 O : Vol. N 



= 1:4:1:2:4. 



