442 Intelligence and Afiscellaneous Articles. 



WHY IRON RAILS WHICH ARE IN USE DO NOT RUST SO RAPIDLY 

 AS UNUSED ONES. BY W. SPRING. 



The fact that iron rails on. those sections o£ a road which are 

 much travelled over do not rust so rapidly as in those places 

 which are not travelled over, or, which are kept in store, has been 

 variously explained but not in a satisfactory manner. According 

 to the author they rust in consequence of atmospheric moisture 

 just like other iron. Whenever a train passes over them the rust 

 previously formed combines under the joint influence of the 

 pressure and friction to form magnetic oxide of iron ; according to 

 the author this proctects the iron in consequence of the electrical 

 polarity which it imparts by making it passive, and thereby pre- 

 serves the rail from further destruction. In confirmation of this 

 explanation the author pressed ferric hydrate between iron plates 

 under a pressure of 1000 to 1200 atmospheres. If the ferric 

 hydrate was dry there was no reaction ; but if the hydrate was 

 moistened with a few drops of water, then, near the iron, it 

 became black and adhered to the metal ; the surface of the plates 

 was visibly attacked, and quantitative analysis showed the presence 

 of magnetic oxide. The author holds that this is the process 

 which naturally takes place. On the surface of the rails, where 

 the wheels pass, he has found magnetic oxide mixed with varying 

 quantities of ferric oxide, and a small quantity of pure iron. — 

 Bull, de VAcad. Roy. de Beige, xvi., p. 47, 1888 ; Beihldtter der 

 PhysiJc, vol. xiii. p. 122. 



EXPERIMENTAL RESEARCHES ON THE TENSION OF THE VAPOUR 

 OF SOLUTIONS. BY F. M. RAOULT, 



The object of the present research is to investigate how far the 

 tension of volatile liquids varies when different solids are dissolved 

 in them. The quantities to be determined are the tensions of the 

 vapour/ of a pure volatile solvent, and then /', that of the same 

 solvent containing in solution a known weight of the solid, the 

 temperature remaining constant. 



Two methods were used — a statical and a dynamical one. The 

 statical is essentially that of Dalton, and consists in measuring the 

 depression produced in barometric columns, when equal volumes 

 of the pure solvent and of the solution are severally introduced. 

 This method, the details of which are described, gives the most 

 accurate results. 



The dynamic method is easily applied when the law is known 

 according to which the vapour-tension of the pure solvent varies 

 with the temperature. It is sufficient then to boil successively the 

 solvent and the solution in the same reflux apparatus, and to note 

 exactly their boiling-points under the atmospheric pressure. In 

 these conditions the vapour-tension of the boiling solution is given 



