610 SCIENCE PROGRESS 



„ H H 2 = OH H a O— OH, H 2 0-OH 2 HX>— OH, 



H,0<g H H 2 0<g H H V || '|| 



uh un< OH OH 2 H 2 0— OH„ H 2 OH 2 



V 

 OH 2 



Hydronol. Dihydronol. Dihydrone. Trihydrone. Tetrhydrone. Penthydrone. 



When a substance such as hydrogen chloride is dissolved, it 

 has no cause to undergo molecular simplification but it may be 

 hydrolated and hydronated in various ways and there is reason 

 to suppose also that it may not only " divide " hydrone but may 

 be " divided " by it, thus : 



HC1<j"jtt H 2 0<Cpt 



A compound such as common salt would behave in a similar 

 manner and perhaps give rise to several compounds with hydrone 

 but being a polymerised substance, such as is represented by the 

 formula (NaCl)x, it would not be completely resolved into the 

 simple molecules represented by the symbol NaCl except in very 

 dilute solutions. 



We have consequently to consider the diffusion not of a single 

 substance but of an unknown number of substances and the 

 problem becomes one of great complexity. It is therefore 

 scarcely probable that we shall ever arrive at any very absolute 

 knowledge of all the separate factors concerned in diffusion. 

 The great lesson we are now learning is, indeed, that the 

 problems are of such complexity that there is little probability 

 that we shall be able to unravel more than the broad outlines of 

 the processes at work in solutions. 



The greatest service rendered to science by Graham in his 

 studies of liquid diffusion is undoubtedly that arising from the 

 distinction he drew between the colloid or jelly-like and the 

 crystalline states of matter and his introduction of colloid 

 membranes or septa as a means of separating the two kinds of 

 substance by what he called dialysis, thus giving the clue to the 

 interpretation of a large class of vital phenomena. No better 

 illustration of the difference can be given than that contained in 

 the following passage from his communication to the Royal 

 Society on Liquid Diffusion applied to Analysis : 



" A sheet of very thin and well-sized letter paper, of French 

 manufacture, having no porosity, was first thoroughly wetted 

 and then laid upon the surface of water contained in a small 



