NEW METHOD OF MEASURING MOLECULAR WEIGHTS. 169 



Weight of benzene in A after 90 hours 8*4401 

 Weight of benzene in B after 90 hours 15*9302 

 Molecular weight calculated, (after 90 hours) = 126*2 



Weight of benzene in A after 108 hours 8*0202 

 Weight of benzene in B after 108 hours 15*1160 

 Molecular weight calculated, (after 108 hours) = 126*2 



The theoretical molecular weight of the unknown was 

 128, which suffices to indicate the degree of accuracy which 

 may be obtained by the method. 



Using ether as a solvent, however, the same measure of 

 success was not obtained, doubtless owing to the evapora- 

 tion which occurred in removing the tubes for weighing. 

 The apparatus used with ether was slightly different in 

 form from that described above. It consisted of two small 

 retorts cut off at the neck and connected by a tightly fitting 

 rubber tube. The evacuation was effected by immersing 

 the bulbs in hot water and inserting the stoppers while the 

 ether was still boiling. The rapidity with which the 

 equilibrium condition was approached with this modification 

 of the apparatus suggests that the time necessary for a 

 determination could be considerably diminished by working 

 at temperatures higher than that of the atmosphere. 



The results obtained by the method first described may 

 be summarised as follows: — 



Solvent. 



Substance 

 determined. 



Substance 

 for comparison. 



Mol. Wt. 

 determined. 



Mol Wt. 



theoretical, 



Benzene 



Naphthalene 



Azobenzene 



126*2 



128 



Benzene 



Azobenzene 



Benzopenone 



181*0 



182 



Ether 



Azobenzene 



Diphenylamine 



173*7 



182 



Water 



Glucose 



Cane-sugar 



160*0 



180 



It will be seen from these figures that the scheme out- 

 lined above affords a satisfactory practical method of 

 molecular weight determination. The ease with which 



