134 DR. B. D. STEELE, DR. D. McINTOSH AND DR. E. H. ARCHIBALD 



vessel containing it weighed. The condensers were then filled with a mixture oi 

 solid carbon dioxide and ether, maintained at atmospheric pressure for the experiments 

 with hydrogen bromide and sulphide, and at reduced pressure for the experiments 

 with hydrogen chloride. 



After the liquid in the vessels had commenced to boil, the vessels were wrapped in 

 natural wool, and the balance point on the bridge was determined. Weighed 

 quantities of the substances whose molecular weight was to be determined were then 

 successively introduced, and the displacement of the balance point was determined 

 after each addition. From these displacements the corresponding rise in boiling-point 

 was calculated. The loss by evaporation, due to the high vapour pressure of the 

 solvents at the temperature of the condenser, was corrected for by means of a blank 

 experiment. 



Evaporation also occurred when the substances were introduced into the apparatus, 

 but as this evaporation was proportional to the amount of substance added, a correction 

 was easily applied. As a check on these corrections, the boiling-point apparatus was 

 removed after each two or three determinations, and when liquid air was available, 

 the apparatus was cooled and weighed. When liquid air could not be obtained, the 

 tube was cooled to a definite temperature, the volume of solution measured, and the 

 amount of solvent calculated on the assumption that no volume change occurred on 

 mixing. 



From the data thus obtained the molecular weight constant was calculated by 

 means of the formula 



M = 



r< A > 

 G A 



in which the molecular weight of the dissolved substance is expressed in terms of y, 

 its weight in grammes dissolved in G-gramme of the solvent, and of the corresponding 

 rise in boiling-point A, K being a constant in the case of a solute which is neither 

 associated nor dissociated. The values of y, G, A, and K for the various substances 

 investigated are given in the first four columns of Tables V, VI, and VII. 

 The following example will show the method of making the calculations : 



Toluene in Hydrochloric Acid. 



Apparent volume of liquid +0'39# toluene. . 38'3 cub. centims. 



). ,, ,, beads ....... 17'0 



Real volume of liquid ......... 21 - 3 



Volume of toluene ......... . . 0'4 



hydrochloric acid ...... 20 '9 



Weight (Part I.) .......... 25%. 



Rise of boiling-point ......... 0'42. 



Constant ........ = 2480. 



