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



floliclus curves, but these unite to form a single solid solution at points 

 on the solidus curve. 



(3) The alloys containing over 80 per cent, of silver do not undergo 

 segregation under ordinary conditions, and are practically homogeneous 

 and uniform in composition. They are well suited as a material for 

 the manufacture of trial-plates. 



"On the Wetting of Cotton by Water and by Water Vapour." 

 By ORME MA.SSON, D.Sc., F.K.S. Eeceived April 25, 1904. 



Introduction. 



If two thermometers, one of which has its bulb protected by a 

 close covering of ordinary cotton wool, be simultaneously immersed 

 in the same water, all being originally at the same temperature, the 

 protected thermometer shows a marked rise, while the naked one 

 undergoes no perceptible change. Heat is, therefore, generated locally 

 by the wetting of the cotton covering. 



The maximum temperature is reached in 2 or 3 minutes, after which 

 there is a fall, the rate of which steadily diminishes in a characteristic- 

 manner, so that, when all necessary precautions are taken, a difference 

 of temperature between the cotton arid the surrounding water is 

 still distinctly perceptible after several hours. Both the extent 

 of the rise and the rate of the whole change depend on several condi- 

 tions. With a given thermometer the most important factors are 

 the quantity of cotton wool, its initial condition with respect to 

 hygroscopic moisture, and the temperature of the water. Other 

 things being equal, the effect is more marked with a large covering 

 than with a small one and at a higher than at a lower bath tempera- 

 ture, but the previous condition of the cotton is a more important 

 factor than either. If taken in its ordinary state after exposure to 

 the air of the laboratory, when it usually contains about 8 or 9 per 

 cent, of moisture, it may show a rise of 2 or 3 C., but if precautions 

 be taken to insure that it is dry at the moment of immersion in water 

 (at its own temperature), the same sample will show a rise of from 

 8 12 or more. 



The relatively large amount of air which is always entangled 

 within the cotton wool does not escape during or after immersion, 

 and the bundle presents a glistening appearance under water which 

 suggests that it is not completely wetted. That this fact is important 

 in connection with the observed temperature change is shown by the 

 behaviour of the so-called " medicated " or " absorbent " cotton wool, 

 which differs from the ordinary (nearly pure) material in having been 

 freed by solvents from traces of natural cotton wax. This gives 







