Intelligence and Miscellaneous Articles. 315 



has become obtuse, and the acid flows in the tube with condensed 

 carbonic acid like quicksilver in a glass tube filled with air. 



In the atmosphere of hydrogen the angle at the margin of the 

 dilute sulphuric acid, which at first likewise wetted the sides, has 

 also increased to about 60°. 



The glass thus appears to have gradually in the course of years, 

 under the influence of the great pressure, become coated with a 

 thin layer of carbonic acid or hydrogen respectively, which exerts 

 a different attraction from that which glass exerts upon the liquid 

 particles at the margin of the surface. A similar film of gas 

 must have been deposited on the surface of the zinc and obstructed 

 the further chemical action of the acid *. 



In spite of the negative result of these experiments, I might 

 not conclude that the molecules of hydrogen and carbonic acid 

 have greater dimensions than the molecules or the pores of glass. 

 The distance within which the molecular forces of glass act upon 

 the gas particles is at all events greater than the dimensions of 

 the molecules themselves. The pore-walls of the glass may be 

 coated with a layer of absorbed gas which, through the vicinity of 

 the solid substance, has itself become immovable, and hinders the 

 passage of the gas particles from the interior of the tube into the 

 outer air. It is also conceivable that there is in the pores of the 

 glass a drop-forming liquid with strongly curved surfaces, which 

 prevents the outflow of the gas, like as under ordinary conditions 

 mercury does not flow out of the pores of a wooden vessel con- 

 taining it. 



A similar objection may be raised against M. Traube's* otherwise 

 ingenious method of determining the relative magnitude of the 

 molecules of a substance from the possibility or not of its passing 

 through a so-called " precipitate-mem brame." He brings together 

 two substances soluble in water, A and B, which at their surface 

 of contact give an insoluble precipitate. This precipitate forms a 

 thin porous skin or a network. The meshes are smaller, M. 

 Traube thinks, than the smallest particles of one of the substances 

 (say A) which have contributed to form the precipitate ; for if 

 they were larger, molecules of the substance A would go through 

 them to the substance B and stop up the apertures with newly 

 formed insoluble precipitate. According to this, the thin skin of 

 " precipitate-membrane " represents a sieve, through which only 

 molecules smaller than its interstices, or smaller than the molecules 

 of the substance A, can pass ; substances with larger molecules 

 cannot diffuse through this sieve or precipitate-membrane. 



But herein the fact is lost sight of that the solid formed by 

 the chemical action of the substances A and B will in general, by 

 selective adsorption, hold different quantities of the three sub- 

 stances A, B, and water at its surface. By the thickness of this 



* Compare Babinet, Ann. de Chim. (2) t. xxxvii. p. 183 ; Faraday, Quart. 

 Journ. iii. p. 374; Gmelin, Handb. d. Cliem. i. p. 126 (1843) ; L. Meyer, Pogg. 

 Ann. vol. civ. p. 189 (1858). 



t Keichert und Dubois-Eeymond's Archiv, 1867, p. 87 segq., "Experiments 

 for the Theory of Cell-formation and Endosmosis." 



