42 MOLECULAR ATTRACTION. L.ECT. II. 



very curious fact, which takes place when we employ a 

 branch with leaves as in all the other experiments of Hales; 

 it is, that the column of water continues to ascend ; so that 

 we are forced to conclude that the vapour of water is ex- 

 haled by the leaves, without these ceasing to act as the 

 accurately closed wall of a barometer. It would appear 

 that Magnus has obtained a like result by closing, with a 

 piece of membrane, the upper part of the tube. From what 

 we have said, the ascension of the column of water should 

 go on, but it is probable that the phenomenon becomes at 

 first less manifest, and then completely ceases on account 

 'of the disorganization which occurs both in the membrane 

 and the leaves. 



Chemical Effects produced by Capillary Forces. I shall 

 not leave this subject without mentioning to you some ex- 

 periments tried with the view of producing by the mere 

 operation of capillary forces and molecular attraction the 

 effects of chemical affinity. If we reflect that any kind of 

 liquid constantly ascends to the same height in a capillary 

 tube ; that during imbibition more or less heat is produced^ 

 as the experiments of Pouillet have demonstrated ; that, 

 moreover, according to Becquerel, there is a disengage- 

 ment of electricity; and, lastly, that capillary attraction is 

 exerted at very minute distances only, and between the 

 molecules of bodies; we cannot deny that this force com- 

 bines the principal characters of chemical affinity. We 

 know the experiment of Doebeireiner, that if a mixture of 

 water and alcohol contained in a bladder be exposed to the 

 air, water constantly escapes from the mixture. In this 

 case the water is imbibed by the membrane more readily 

 than the alcohol, and is dissipated by evaporation. 



Salt Water made fresh by Filtration. Another and more 

 conclusive fact is mentioned by Berzelius : a saline solution 

 filtering through a long tube filled with sand runs out more 



