TRANSACTIONS OF SECTION B. 



693 



Analogous arrangements would represent the double chlorides. These examples 

 were given in the author's original paper eleven years ago, and are the same aa 

 those which were given by Professor Schutzenberger in June last. 



In 1878, in another paper, the author stated that from the behaviour of clay in 

 water and other experiments he had come to the conclusion that in chemical com- 

 pounds the affinity is not all exhausted in all cases, but that sometimes enough 

 remained to give rise to solution and suspension phenomena, and that there is a 

 regular gradation between chemical combination, solution, and suspension. The 

 idea of residual affinity has now been adopted by many chemists, and lately Messrs. 

 Picton and Linders, from experiments on solution of sulphites, have also come to 

 the conclusion that there is no hard-and-fast line between solution and suspension. 

 This confirms the conclusion which the author drew from his experiments of 

 fourteen years ago. 



14. On a Method for Determining the Vapour-j)ressures of Solutions. By 

 Thomas Ewan, B.Sc, Ph.D., 1851 Exhibition Scholar at the Owens 

 College, and W. R. Obmandy, Bishop Berkeley Fellow at the Owens 

 College. 



M. G. Charpy has pointed out in the ' Comptes Rendus ' for 1890, p. Ill, the 

 possibility of using a condensation hygrometer of Regnault's form for the determi- 

 nation of the vapour-pressures of solutions. The paper contains a description of 

 some experiments which we have made with this method. 



The solution to be examined was placed in a cylindrical vessel, 4'5 cm. in 

 diameter and 13'5 cm. long, with a narrower neck 20 cm. long. The solution was 

 stirred by means of a ring of platinum wire attached to a light glass rod. The 

 hygrometer, consisting of a single silver cup attached to a glass tube 22 cm. long, 

 slipped loosely into the vessel containing the solution, was suspended about half 

 an inch above its surface. 



The whole apparatus was placed in a water-bath, which could be kept at a 

 constant temperature. 



The readings of the dew-point were made by observing the temperature at 

 which the first traces of dew appeared on the hygrometer. The vapour-pressure of 

 water corresponding to the temperature of the dew-point was taken from Regnault's 

 tables. The number so obtained is the vapour-pressure of the solution at the tem- 

 perature of the water-bath. 



The accm-acy of the method was tested by a number of readings with 



(a.) Water. 



(b.) Solutions of NaCl and CuCl,,. 



Table I. contains the readings made with water ; the dew-point should coincide 

 with the temperature of the water. 



Table I. 



Sodium Chloride. 



Table II. contains a comparison of the values of ///' ( / being the vapour-pres- 

 sure of water, and f that of the solution) obtained by ourselves and by other ob- 

 servers. is the concentration of the solution in gramme molecules of NaCl in ] ,000 

 grammes of water. 



