364 Dr. A. Kansorne on some of the 



of particles in any transverse section of the column of liquid and 

 their distance from one another, it might be possible to calculate 

 the force exerted ; but it is needless to say that at present this 

 knowledge is withheld from us. 



It is interesting to notice the part played by the attraction of 

 cohesion in this case. It has recently been shown by M. Jamin 

 (Comptes Rendus, vol. 1. p. 172) that when successive beads of 

 fluid are contained in a capillary tube, the resistance offered by 

 the cohesive force of these beads may be so multiplied that they 

 will resist considerable pressure, even to 3 or 4 atmospheres. 

 Mercury produces still greater effects; but, on the other hand, 

 alcohol and oil oppose no resistance to pressure. 



The same variation, from the varying molecular force of differ- 

 ent substances, is also observed in experiments on capillarity; 

 and, in relation to this subject, it may be mentioned that the 

 magnitude of drops of fluid distilled from a tube is in proportion 

 to the weight of that fluid raised in that tube by capillary attrac- 

 tion — the chemical composition of the liquid affecting the weight 

 of its drop in a remarkable manner*. 



Mixtures. — Mixtures of different fluids afford perhaps the 

 simplest examples of the varying extent to which molecular affi- 

 nity may be manifested. 



Some fluids will mix in any proportions with one another — for 

 example, alcohol, and glycerine and water. Others, again, as 

 ether and water, at the same temperatures will only mix in cer- 

 tain fixed proportions. 



In order that two fluids may be entirely miscible, it seems 

 necessary that the particles of each fluid have for those of the 

 other a greater molecular affinity than they have amongst them- 

 selves; in other words, the molecular attraction of one fluid for 

 the other must be sufficient to overcome the cohesive forces 

 of eachf. 



When fluids are only partially miscible, we can conceive that 

 up to a certain point the particles of one fluid are so separated 

 from one another by those of the other fluid that their cohesive 

 forces cannot draw them together ; but as soon as the solution 

 becomes more concentrated and the particles get sufficiently close 

 together, then the cohesive forces gain the ascendant, no further 

 mixation can take place, and saturation is the result. 



Molecular attractions of Vapours and Gases. — Gases and va- 

 pours also display certain degrees of molecular affinity in their 

 relations to one another, gases being susceptible of mixture with 

 other vapours up to a certain point of saturation. 



* Phil. Mag. S. 4. No. 181. 



t The contraction of volume which takes place in some fluids after mix- 

 ture gives considerable probability to this opinion. 



