New Method of determining Vapour Pressures of Solutions. 285 



also the traction between the interfaces when it is divided : and 

 the mode of calculation of the stress in a sphere of iron in a uniform 

 magnetic field is indicated, agreeing for this case with Kirchhoff. 

 The mutual influence of stress and magnetisation is analysed, with 

 reference to the experimental investigations of Bid well. 



Throughout the memoir care is taken to dispense, as far as possible, 

 with detailed algebraic processes, which are essential for special 

 computations and verifications, but are best evaded in the discussion 

 of general principles. Most of the discussion is also independent of 

 the rotational aether scheme : the great advantage of an interlacing 

 hypothesis of that kind, which remains even when it is only pro- 

 visional, is that it gives an insight into the character of the formal 

 relations that are possible or probable between the actual physical 

 quantities involved in it. 



* Oil a new Method of Determining the Vapour Pressures of 

 Solutions." By E. B. H. Wade, B.A., Scholar and Coutts- 

 Trotter Student of Trinity College, Cambridge. Com- 

 municated by Professor J. J. Thomson, F.R.S. Received 

 April 26 —Read May 13, 1897. 



(Abstract.) 



The measurement of the vapour tension of solutions has hitherto 

 been attended with serious errors. This is especially true of the 

 statical methods, which have alone been capable hitherto of furnish- 

 ing results at temperatures between 60° C. and 100° C. 



The apparatus employed in this research was in conception similar 

 to that described by Sakurai,* except that it was in duplicate, a 

 divided steam supply passing through twoU-tubes placed in parallel. 

 It differed, however, from his apparatus in several important features, 

 which cannot adequately be described in a paper of these dimensions. 

 Suffice it to say that the pressure on the contents of the two U-tubes, 

 being the same, could be adjusted to any convenient value, and that 

 the method of thermometry being differential,! the difference only of 

 the boiling points of pure water and solution, in their respective 

 U-tubes was recorded. Two series of experiments were made at a 

 pressure of 760 mm., in one of which a small external heat supply 

 was used to compensate the condensation in the I' -tubes, and a second 

 in which this was dispensed with, and constancy in the amount of 

 liquid operated on (which proved to be of the first importance) was 



* ' Chem. Soc. Journ.,' 1892. 



f Identical with that employed for many years by Mr. Griffiths. 



