of hydrogen by carbon and concludes that a portion is really adsorbed 
and that another portion forms a solid solution. 
GrorGigvics'),. in his later investigations as to the absorption of 
dilute acids by wool, has also come to the conclusion that in many 
cases adsorption and solid solution oecur together. From very dilute 
solutions, acids as well as different colouring matters with a constant 
division factor are absorbed so that this absorption may be considered 
as a true solid solution. 
Adsorption and solution, therefore, go hand in hand and in most 
cases it is difficult to make’ out what part appertains to each of 
these phenomena. 
When the nature of the absorbing material causes the diffusion 
towards the interior to take place with extreme difficulty, as in the 
case of carbon and silicates, the formation of a solution will take 
place in the external layers of the substance only and one will get 
the impression of dealing with a mere surface action or adsorption. 
In some cases, however, it appears that the colouring matter has 
penetrated further into the substance. Silicates coloured by fuchsine 
and methylene blue exhibit a distinct pleochroism *), which shows that 
the dyestuff has distributed itself homogeneously nto the silicate and 
has not deposited merely on the surface. 
Cases of true adsorption will occur when the substance is dissolved 
in the colloidal state and does not dissolve molecularly in the absorp- 
tion medium. We may then expect either no absorption at all or a 
complete absorption as colloidal solid solution, or else a complete 
separation of the colloid at the border layer; this then constitutes 
adsorption. Instances of this are found in the adsorption of colloidal 
gold by carbon or by BaSO,*), of As,S,-solution by carbon or by 
BaSO,, of a very fine carbon suspension by paper *) and also in the 
dyeing of wool or cotton with some undoubtedly colloidal dye 
solutions such as that of the blue acid of congo-red. This colouration 
however, is not permanent and can be completely removed by washing’). 
How does a dyestuff distribute itself over two solvents? 
In this direction but few determinations have been made. Only 
in the case of pierie acid the distribution between water and 
1) Koll. Zeitschr. 10, 31 (1912), 
2) T. Cornu, Tschermak’s Mineralogische und Petrographische Mitteilungen 1906, 
453. 
8) L. Vanino, Berl. Ber. 35, 662 (1902). 
4) Spring, Beobachtungen über die Waschwirkung der Seifen. Koll. Zeitschr. 
4, 161 (1909). 
5) Perer-Jouver, Die Theorie des Färbeprozesses, p. 141 
