ASPECTS OF ADSORPTION PHENOMENA 193 



the phenomena met with, although of considerable interest,- showed 

 themselves to be of a very complex nature, so that it will be better to 

 devote a special section to the discussion of them later on. 



At first sight the action of heat in dissociating the adsorption 

 compound, as above described, appears at variance with the common 

 practice of histologists in staining their preparations. I find that the 

 beneficial effect of heat in this case is probably due to the fact that a 

 piece of paper, for example, dyed with congo-red and exposed to a 

 temperature of iooC. loses the power to a large extent of giving up 

 the dye to water, in other words it is fixed more firmly than if merely 

 stained at room temperature. 



According to the well-known laws of Van't HofF, since the com- 

 pound of cellulose and congo-red is dissociated more and more as the 

 temperature rises, the formation of the compound should be accompanied 

 by evolution of heat. I have attempted in various ways to detect 

 such a production of heat but have been unable to do so. The two 

 methods used were : (i) Immersion of a Beckmann thermometer in the 

 centre of a series of co-axial cylinders of filter paper in a large beaker 

 filled with Nad solution to facilitate adsorption. A test-tube of I per 

 cent, solution of congo-red was also immersed in the solution, and 

 when the whole was at the same temperature, the dye was mixed with 

 the saline solution. No temperature change was to be observed, 

 although by aid of a lens, the thermometer could be read to 

 r^-th of a degree ; (2) A disc of paper moist with Nad solution was 

 allowed to rest on the face of an ordinary bismuth-antimony thermo- 

 pile contained in a vacuum-jacketed vessel and connected to a 

 low-resistance d'Arsonval galvanometer. The vessel also contained 

 a small tube of concentrated congo-red solution, closed at the bottom 

 by a glass rod with indiarubber tube around its lower end. When 

 the galvanometer was steady the glass rod was raised and the dye 

 allowed to flow over the paper. No deflection indicating the 

 production of heat was observed. It is to be noted, however, that 

 at the temperature of these experiments, the process would not be 

 very rapid, and it is possible that a slight heat production would bj 

 conducted away as fast as it was formed. 



