252 Dr. 0. Masson. On the Wetting of [Apr. 25, 



means attained its full growth and, in fact, threatened to increase 



indefinitely. 



It seems probable, therefore, that the deposited moisture does not all 

 remain as a mechanically adherent film on the surface of the cotton; 

 and the third hypothesis may be suggested. This is, that it undergoes 

 continuous osmotic diffusion into the substance of the fibre and forms 

 with it what may be regarded as a solid solution of cellulose and water. 

 Such a solution would exercise a vapour pressure of its own which 

 would, at anything less than infinite dilution, be smaller than that of 

 pure water at the same temperature. In a saturated atmosphere there- 

 fore equilibrium would never be reached, though the velocity of the 

 absorption process would decrease continuously as the solution became 

 more dilute. The heat developed locally by the action, i.e., the heat due 

 to the deposition of the liquid plus or minus a small heat of solution, 

 would go to raise the temperature of the cotton above that of the neigh- 

 bouring water by which the vapour is supplied, and would thus tend to 

 check the action by increasing the vapour tension of the solution; but the 

 natural cooling by radiation, etc., would again act as a counter-check. If 

 placed in an atmosphere containing water vapour at anything less than 

 saturation pressure (e.g., in the open air) the cotton would, in time, 

 reach a state of equilibrium either by absorption or by evaporation, 

 according to its initial condition, and it would part with all its water if 

 the surrounding atmosphere were maintained in a perfectly dry state, 

 slowly or quickly according to the temperature. This is all in accord- 

 ance with the ascertained facts, and as it is also inherently probable 

 that the cotton fibre is permeable by water, the hypothesis appears to 

 be justified. 



As solids in general have the power of condensing vapours on their 

 surface, it was not surprising to find a marked heat development on 

 immersing cotton wool in air saturated with the vapour of absolute 

 alcohol, gun-cotton in air saturated with water vapour, and glass wool 

 in the same ; but the effect was considerably smaller than when cotton 

 wool was immersed in water vapour under similar conditions. In the 

 case of glass wool the temperature curve was taken and weighings were 

 made so as to determine the amount of vapour absorbed. The thermo- 

 meter was wrapped as closely as possible with the material, which was 

 secured by a few turns of fine aluminium wire, and the other arrange- 

 ments were the same as in Series V. The glass wool weighed, after 

 drying, 1-22 gramme. The diameter of the fibres was measured under 

 the microscope and was found to vary from about O'OOl - 003 cm. 

 It would have been necessary to make a large number of measurements 

 to determine an accurate mean value, but O0025 cm. may be taken as 

 near the mark; and this, with a density of 2*7, would make the total 

 area of surface about 720 sq. cm. or about 0'57 of the area exposed by 

 the cotton wool of Series V. The maximum rise was 1'94 and 2'l in 



