i 3 o SCIENCE PROGRESS. 



at ioo° C, after which it increased rapidly as the pro- 

 portion of hydrogen in the solid increased. The analogy 

 between this case and the case of the solubility of mixtures 

 of /3-naphthol and naphthalene in water is at once apparent. 

 In both instances we have constancy of pressure (gas- 

 tension) and solubility (solution-tension) within a certain 

 range of composition, and then rapid variation with further 

 change of composition. The conclusions arrived at in both 

 instances are also similar. The constant solubility was 

 attributed by Klister to the formation of a compound 

 naphtholnaphthalene — the constant tension was attributed 

 by Troost and Hautefeuille to the formation of a compound 

 Pd 2 H, in which any excess of hydrogen was then absorbed. 

 Quite recently, however, grave doubts have been thrown 

 on the existence of this compound. A very careful repetition 

 and extension of Troost and Hautefeuille's experiments by C. 

 Hoitsema has proved that the constancy of tension observed 

 by these investigators was not absolute but only approxi- 

 mate, and that under slightly varying conditions the 

 apparent constancy disappeared altogether. It would 

 seem, therefore, that no compound of palladium and hydro- 

 gen is formed when the gas is absorbed by the solid, the 

 state of the hydrogen being rather one of simple solution 

 in the palladium. A comparison of the concentrations of 

 the hydrogen above the palladium and of the hydrogen in 

 the palladium indicates that at very low pressures the 

 hydrogen in the metal exists as molecules only half as great 

 as those of the gas, i.e., as molecules consisting of only one 

 atom. At higher pressures the concentration of the free 

 gas and that in the palladium stand in a nearly constant 

 ratio, from which it is to be inferred that the molecule of 

 hydrogen in the metal, as well as the molecule of gaseous 

 hydrogen, is represented by the formula H 2 . 



A problem which has long interested chemists is the 

 determination of the nature of the process involved in dyeing. 

 Some contended that the process was one of chemical union of 

 the dye with the substance of the fibre, others that it was 

 merely one of mechanical absorption. In 1890, however, 

 O. N. Witt propounded a new theory which, on account of 



