IN.S.'] 



] 



J^ 



yf gases, etc. 23f^' 



Japers; — G. C. Schmidt, Ghent. Soc, Ahs, 1895, A, ii., 39 ; 

 . Walker, Chenu Soc. Trans. 1896, 1334; P. D. Zacharias, Chem. 

 Soc. Trans. 1902, ii., 249, i., 635, 725, 



The absorption curves resemble those shown in Plate I, tlie 

 ordinates repi^esenting tlie concentration of the dye in the solution, 

 and the abcissa? the concentration in the fibre. When the value 

 of n in the expression, which may be written 



n ^^(Concentration in soln.) /(Concentration in fibre) 



Constant, 



is lai^ge, and the curve resembles the one on the left hand of the 

 plate, an interesting condition is arrived at. The fibre or other 

 amorphous substance appears to take up the whole of the soluble 

 material in the bath till a certain concentration is arrived at. In- 

 crease in the concentration in the bath above this limit does not 

 appear to be accompanied by marked increase in the quantity of 

 soluble matter absorbed. That this should be so is evident from 

 the form of the curves. 



As far as we know it is not possible to colour crystalline sub- 

 stances, except by depositing colouring matter on the surface of 

 the crystals; they cannot be dyed in the true sense of the word^ 

 though isomorphous mixtures of coloured and colourless substances 

 may be formed by crystallising mixed solutions. 



[My attention has been called to a paper by Masson and 

 Richards ' On the Hygroscopic Action of Cotton/ which appeared 

 in the number of the '* Proceedings " of the Royal Society published 

 on December 20th (Vol. 78, p. 412). The experimental results 

 obtained by these authors resemble my own, but they are obtained 

 as the mean between the values for the quantities of moisture 

 absoi^bed by dry cotton under certain conditions of temperature 

 and saturation of the atmosphere, and for the quantities retained 

 by moist cotton under similar conditions. The method is by no 

 means accurate when applied to the measurement of small vapour 

 pressures, and it may be for this reason thnt my results do not 

 confirm the authors' conchisions as to the variation of pressui-e 

 with temperature at constant saturation (p. 426, § 2). 



The authors confine their attention to the case of the absoi-ji- 

 tion of moisture by cotton, and in a 2)ostscript discussing Trouton's 

 expex^iments they point out that * the pure surface theory . . • is 

 inconsistent with the facts,* but that it appears more probable 

 that * the film of moisture does (until equilibrium is reached) pene- 

 trate and form a species of solution/ 



This was the conclusion at which I arrived when the experi- 

 ments referred to in my paper were completed, and I expressed 

 my views in a paper read before the Sanitary Congress last sum- 

 mer. The object of the present paper is to call attention to the 

 fundamental principles which underlie the phenomenon of absoip- 

 tion, and to the distinction which must be drawn between 'solid 



solutions' and solutions which are formed by amorphous sub- 

 stances,] 



