NEW METHOD OF MEASURING MOLECULAR WEIGHTS. 1 67 



vapour pressure they must also be in equilibrium as regards 

 their osmotic pressures. In other words the concentratiou 

 of dissolved particles is the same in each solution. 



Upon this condition we have 



1H _ 1l 2 



Vi v 2 



where Vi and v 2 denote the volumes of liquid in the vessels 

 A and JB and in and n 2 the number of dissolved molecules 

 in these respective solutions. Hence, if mi and m 2 are the 

 molecular weights of the two solutes, and wi and iv 2 the 

 weights of solute added to each side, 



_ IV i ffl2 t>2 _ Wi m 2 W 2 



vi iv 2 Wi w 2 



where Wi and W 2 are the weights of liquid in the vessels 

 A and B. The actual form of the apparatus employed to 

 determine molecular weights on the above principle is 

 represented in the accompanying diagram (Fig. 1). The 

 tubes A and B are ground into the connecting limb C, by 

 which the two solutions are placed in communication. The 

 space above the liquids was exhausted of air in order to 

 secure more rapid distillation from one side to the other. 

 Stirring of the solutions was accomplished by placing glass 

 rods in each of the tubes A and B and then rocking the 

 whole apparatus on a mechanical rocker of special con- 

 struction. 



In order to conduct a molecular weight determination 

 with the above apparatus, all that was necessary was to 

 place a weighed quantity of the substance (solute) in one 

 of the tubes, and a weighed quantity of some other sub- 

 stance of known molecular weight in the other tube. Each 

 of the tubes was then filled about two-thirds full of some 

 liquid solvent, in which both of the substances were soluble. 

 The exact amount of solvent added to either tube is im- 

 material. After fitting the tubes into the connecting limb, 



