452 Mr. Graham's Recent Di 



iscovcries. 



MR. GRAHAM'S RECENT DISCOVERIES : — THE 

 ABSORPTION AND DIALYTIC SEPARATION OF 

 GASES BY COLLOID SEPTA :— THE OCCLUSION OF 



GASES. 



In a series of papers communicated to the Roj^al Society, Mr. 

 Graham has detailed his beautiful researches into the diffusion 

 of gases. The subject of this paper is a brief account of his 

 recent researches on the Absorption and Dialytic Separation 

 •of Gases by Colloid Septa. 



It is necessary to remember that all gases when existing 

 under circumstances in which they do not chemically combine, yet 

 diffuse themselves through one another and form a uniform mix- 

 ture, even though their specific gravities may be widely different, 

 and they be kept externally at perfect rest ; the law being that 

 this tendency to diffuse varies in the inverse ratio of the square 

 roots of their specific gravities. It must also be borne in mind 

 that the same law regulates the diffusion of gases through 

 septa possessing minute pores as when the gases communicate 

 freely with each other. 



Mr. Graham has shown how a mixture of gases may be 

 changed in composition by the escape of the lighter and, there- 

 fore, more diffusible gas, this fact being well shown bypassing 

 an explosive mixture of one volume of oxygen and two volumes 

 of hydrogen through the stem of a tobacco-pipe enclosed in 

 an outer tube of glass, which is rendered vacuous, the hydrogen 

 being more diffusive, streams through the porous walls so much 

 iaster than the oxygen that on issuing from the end of the pipe 

 the mixture ceases to be explosive. But mixed gases must differ 

 considerably in specific gravity in order to separate from one an- 

 other to any great extent in their molecular passage into vacuum. 



In his recent researches Mr. Graham has employed — firstly, 

 the soft colloid, india-rubber; secondly, those metals to which 

 a certain degree of colloid property might be imparted by 

 means of heat. 



When atmospheric air is separated from a vacuous space by 

 a septum, or bag of india-rubber, some air passes through 

 it into the vacuum. In observing the passage of air 

 and gases into vacuum, the Torricellian vacuum was first 

 employed. A plain glass tube, two millimetres in diameter 

 and one metre in length, is closed at one end by a sheet of 

 thin india-rubber strained over a porous plug of plaster of 

 Paris, the tube is now filled with mercury and inverted, a 

 vacuum being obtained into which 'air (or any gas allowed to 

 play upon the disk of rubber) gradually penetrates, passing 

 through the film and depressing the mercurial column in the 



