THE GREAT LONDON CHEMISTS 63 



the molecules, it follows that a molecule of hydrogen 

 moves through space four times as rapidly as a molecule 

 of oxygen. This law was confirmed by measurements 

 made on many other gases. These experimental re- 

 searches of Graham's have been one of the chief supports 

 of the kinetic theory, devised long afterwards, on the 

 assumptions that the pressure of gases is due to the im- 

 pacts of their molecules on the walls of the containing 

 vessel, and that their temperature is to be ascribed to the 

 rate of motion of the molecules. 



Much later, in 1849, Graham investigated the rate of 

 flow of gases through narrow tubes, and obtained results 

 which have also been found of incalculable service to the 

 theory of gaseous matter. 



A few years later, in 1851 and 1852, Graham published 

 investigations on the diffusion of liquids, a subject follow- 

 ing close on the lines of his former work on the diffusion 

 of gases. His plan of experiment was as simple as it was 

 well adapted to furnish the information sought. A wide- 

 mouthed bottle was filled with the solution of a salt, and 

 placed inside a wider jar; the jar was then carefully filled 

 with water, care being taken not to disturb the level of 

 the solution in the bottle. The apparatus was then left 

 to itself for a considerable time. It was found that the 

 salt did not stay within the bottle, but gradually escaped 

 into the jar. The amount escaping in different times and 

 at different temperatures was measured. 



Experiments made on a great variety of substances soon 

 revealed the fact that some substances escape much more 

 rapidly than others. For instance, Graham found that 69 

 parts of sulphuric acid, 58 of common salt, 26 of 

 sugar, 13 of gum-arabic, and only 3 of egg-albumen 

 escape in equal times, other circumstances being equal. 

 Some other substances, such as potassium and ammonium 

 chlorides, potassium and ammonium nitrates, magnesium 



