STUDY OF MOLECULAR ADHESION. 415 



substances in the form of gases or solutions (electrolytes, colloidal 

 sols). These adsorption phenomena by solid bodies bear a definite 

 relation to the considerable surface development of the particles 

 of these substances. Colloids in the state of gels, which also have a 

 large surface, are likewise endowed with energetic adsorption 

 properties.* The laws of adsorption by solid bodies are the same 

 as with colloidal gels. 



The phenomena of molecular adhesion may begin between two 

 substances of different natures and may also occur between the 

 particles of the same substance, for example, the particles of an 

 insoluble solid suspended in water. If increasing amounts of a 

 suspension of barium sulphate in water are added to a constant 

 volume of water, we find that the mixture becomes cleared of the 

 powder with a rapidity which varies directly with the amount of 

 barium sulphate added. Naturally this is due to the fact that the 

 nearer the particles are to one another the more their mutual ad- 

 hesion is facilitated and they form clumps which sediment more 

 easily. The sedimentation of a substance which is insoluble in 

 water is, as we know, facilitated by certain colloidal solutions 

 and viscous fluids.! A few years ago Mullerf studied the inhibit- 



* Van Bemmelen, Zeitschrift fur Anorg. Chem., 1900, 23. This author has 

 suggested the name of adsorption to designate the accumulation of gas or fluids 

 in porous bodies or on the surface of non-porous bodies, and the word absorption 

 for the instances in which the molecules of the adsorbed substance interchange 

 with those of the adsorbing substance, for example, homogeneous solutions of 

 gases, liquids or solids. The phenomena which we are about to consider deal with 

 the adhesion of various substances to solid bodies suspended in a fluid, and we 

 prefer to use the term adsorption. 



t Lobny de Bruyn (Rec. des Trav. chim. des Pays Bas, 1900, vol. 19) has 

 shown in particular that if solutions of salts which normally form an insoluble 

 precipitate are added to gelatin the sedimentation occurs much more slowly. 

 The reaction between these salts, however, takes place just as well under these 

 conditions, for the rapidity of the reaction is as rapid in gels as in water. 



(E. Cohen, Eder's Jahresbericht f. Photographic, 1895, cited by Hamburger, 

 Osmot. Druck u. lonenlehre, vol. 3, p. 89. 



Rothland, Zeitschrift f. anorg. Chem., vol. 40; Spring, Bull, de 1'Acad. Roy. 

 de Belg., 1900, p. 515.) 



Since this time several authors have applied the same method and similar 

 . methods in preparing colloidal solutions of substances that are usually insoluble. 



Paal and Amberger: Bericht d. deutschen chem. Gesellschaft, vol. XXXV and 

 XXXVII; Paal and Voos, Ibid, vol. XXXVII; Lottermoser, Ueber anorg. 

 Kolloide, Stuttgart, 1901; Guthier: Zeitschrift f. anorg. Chem., XXXII. Hein- 

 rich, Bericht d. deutsche chem. Gesellschaft, XXXVI; Garbowski: Ibid; Carey 

 Lea, Ibid, XXIV.) 



J Bericht d. deutschen chem. Gesellschaft, 1904. 



