AND EXOSMOSE. 7 



dipped into it, while quicksilver does not; and chemical afi&nity, 

 whereby particles of one substance attract and enter into combinar 

 tion with particles of another substance with which they may be 

 combined, as in a solution of soda-water powders the tartaric acid 

 attracts the soda from the carbonate of soda and combines with it, 

 leaving the carbonic acid with which it was combined disengaged and 

 free to escape as it does in the effervescence which it occasions. 



A clear conception of the differences thus indicated will make the 

 process of endosmose and exosmose more intelligible. In the illustra- 

 tions of adhesion which I have given, the attraction of adhesion 

 between the finger and the quicksilver was of less force than the 

 attraction of cohesion by which the particles of matter of which the 

 finger is composed, and than the attraction of cohesion by which the 

 particles of quicksilver are held together, and the finger could be 

 withdrawn unbroken leaving the quicksilver entire. But in the 

 other cases mentioned the attraction of adhesion, though less in force 

 than the cohesion betwixt the particles of matter of which the finger 

 is composed, was greater than that by which the particles composing 

 the water, the treacle, or the tar were held together, and this giving 

 way a portion adhered to the finger. 



In the endosmose taking place in the case adduced for illustration 

 the adhesion to the bladder of the water in the basin must have been 

 greater in force than the attraction of cohesion by which the particles 

 of water were held together, and the chemical affinity of the saline 

 solution within the bladder for the water greater in force than the 

 attraction of adhesion by which it was held by the bladder. From 

 the moistened tissue of the bladder, water by which it was moistened 

 was attracted by and combined with the saline solution; this was 

 replaced by more from the basin, which in like manner was with- 

 drawn, and the process went on continuously, producing the pheno- 

 menon of endosmose. 



The process of exosmose was similarly produced : the force of 

 adhesion between the saline solution and the inside of the bladder 

 was greater than the force of cohesion by which the particles of that 

 solution were held together ; but the chemical affinity of the water 

 in which the bladder was immersed for that saline solution was still 

 greater in force tJian that adhesion, and thus a portion of the saline 

 solution was withdrawn and combined with the water in the basin. 



This is not given as a full explanation of all the phenomena of 

 endosmose and exosmose, but as an explanation of the more striking 

 phenomena produced, which is all that is required for the object in 



