xix 



Thomson's * Annals of Philosophy/ 1826, " On the Absorption of 

 Gases by Liquids." He there reasons out the idea that gases are con- 

 verted into liquids by mixing with or being absorbed by liquids, and 

 that the phenomenon becomes simply that of two liquids mixed together. 

 He concludes that gases may owe their absorption by liquids to their capa- 

 bility of being liquefied, and to the affinities of liquids to which they 

 become in this way exposed. These two properties are considered to be 

 the immediate or proximate causes of the absorbability of gases. It follows 

 " that solutions of gases in liquids are mixtures of a more volatile with a 

 less volatile liquid." He says also that it is a coincidence more than ac- 

 cidental that the gases which yielded to condensation in Mr. Faraday's 

 hands are, generally speaking, of easy absorbability. He objects therefore 

 to Henry's law, that the quantity of gas which water absorbs is directly 

 proportionate to the pressure, because it is not likely that this law would 

 have been spoken of had such gases as muriatic acid been employed, that 

 being very readily absorbed, although there might be an approximation 

 to such a law when the quantity of gas absorbed was inconsiderable. 



Graham illustrated the condensation and solution of a vapour in a liquid 

 by supposing steam of the heat of 600° F. to be passed through sulphuric 

 acid of 600° F., when he doubted not immediate absorption and actual 

 solution would take place, as if water and sulphuric acid were mixed at 

 lower temperatures ; and yet the steam would be brought into the condition 

 of a liquid which by ordinary cooling would have taken place only after 

 nearly 400° diminution of temperature. 



So late as 1866, speaking of the dialytic separation of gases through 

 colloid septa, he is desirous of showing that the flow is not that of diffusion 

 or of effusion, or of transpiration, but that of a liquid absorbed by one side 

 and passed to the other ; and in 1868 he illustrates the passage of hydrogen 

 through palladium by saying that it is analogous to liquid diffusion through 

 a colloid. There are forty years between the beginning and end of this 

 train of thought. 



This is a fair specimen of Graham's habit of mind and of his perseve- 

 rance. He seems to have begun life with an intense desire to know the inner 

 structure of matter, stimulated to understand more than the atomic theory 

 could give him, but nevertheless a true student of Dalton. Born in 1805, 

 when Dalton was preparing for the press the ideas he had already given in 

 lectures, he seems to have been destined to begin anew line of work closely 

 allied to that which Dalton had done. 



It is almost painful to think of the attempts of mankind to understand 

 why bodies should have a definite composition, and Dalton's simple idea 

 of adding atom to atom not only made it appear possible, but showed why 

 the contrary should be most improbable. Now it seems so simple that 

 some men believe it was scarcely a discovery, whilst every chemist is slavishly 

 bound to it in some form or other, unable either in practice or theory to 

 escape ; and this point seems now to be true for all time. Still the simple 



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