120 21emoir of Thomas Graham. 



These facts recall the i 



between the qualities of an alloy and 1 __, ^„ 



metals, and suggest the inference made by Grraham, that palla- 

 dium charged with hydrogen is a compound of the same class, 

 —a conclusion which harmonizes with the theory long held by 

 many chemists, that hydrogen gas is tlie vapor of a very vola- 

 tile metal. This element, however, when combined with palla- 

 diura, IS in a peculiarly active state, which sustains somewhat 

 the same relation to the familiar gas that ozone bears to ordinary 

 oxygen. Hence Graham distinguished this condition of hydro- 

 gen by the term "Hydrogenium.'' Shortly before his death a 

 medal was struck at the Eoyal Mint from the hydrogen palla- 

 dium alloy m honor of its discovery ; but although this discov- 

 ery attracted public attention chiefly on account of the singular 

 chemical relations of hydrogen, which it brought so prominently 

 to notice, it will be remembered in the history of science rather 

 as the beautiful termination of a life-long investigation, of which 

 the medal was the appropriate seal. 



Simultaneously with the experiments on gases, whose results 

 we have endeavored to present in the preceding pac^es, Graham 

 earned forward a parallel line of investigation of an allied class 

 of phenomena, which may be regarded as the manifestations of 

 molecular motion m liquid bodies. The phenomena of diffusion 

 reappear m liquids, and Graham carefully observed the times in 

 which equal weights of various salts dissolved in water diffused 

 Irom an open-mouth bottle into a large volume of pure water, 

 m which tbe bottle was immersed. He was not, however, able 

 to correlate the results of tliuse expcrinicut^ bv such a simple 

 aw a^ that whix^h obtains wirl. gas.s.^ It apt.^nvd, nevertheless, 

 that the rate of ditfusion.liin'is vcrv -n- t v for the different 

 soluble salts, having some relation to the dlnnu'd comp-ition 

 of tlie salt which he was unable to disccner.' But he found it 

 possible to divide the salts into groups of equi-diffusive sub- 

 stances, and he showed that the rates of diffusion of the several 

 groiips bear to one another simple numerical ratios 



More important results were obtained from the study of a 

 Class ot phenomena corresponding to the transpiration of gases 

 through india-rubber or metallic septa. These phenomena, as 

 manitested m the transfer of liquids and of salts in solution 

 frJnn! fl . ^^^'''' a similar membrane, had previously been 

 irequently studied under the names of exosmose and end^smose, 

 put to Lrraham we owe the first satisfactory explanation. As 

 m me case of gases, he referred these effects to the influence of 

 cJiemical force, combination taking place on one surface of the 

 membrane, and the compound breaking up on the other, the 

 difference depending, as in the previous" instance, on the influ- 

 ence 01 mass. He also swept away the arbitrary distinctions 



