84 THE ROYAL SOCIETY OF CANADA 



Then either the acid solution is forced back by the return of the 

 meniscus after wetting, which is not at all likely, or it creeps up of 

 itself between the acid and mercury. 



In a paper on the Angle of Contact^ it was shown that when the 

 angle of contact made with glass by a mercury surface covered with 

 dilute sulphuric acid is zero, the acid creeps between the mercury and 

 glass. Further experiments show that this creep always occurs with 

 H2SO4 at least when the concentration is higher than one-half of one 

 per cent. A large number of tubes was prepared by washing with 

 aqua regia, water, potassium hydrate and distilled water. Distilled 

 mercury was placed in the tubes and covered with dilute sulphuric 

 acid. Many different sizes of tubes were used in order to study a 

 possible effect depending on the diameter of the tube. While the 

 smaller tubes seem to have a larger creep than the larger ones, the 

 occurrence of rapid creep among the large and of small creep among 

 the small tubes render such a conclusion doubtful. 



The curves for the creep plotted as total distance against the 

 time are approximately exponential. The acid creeps rapidly during 

 the first few hours and then more and more slowly until it becomes 

 almost stationary. Its rate depends so much on the cleanliness of the 

 glass surface that the line between the wetted and unwetted portion, 

 which is very sharp and distinct at first, becomes less and less distinct 

 until it is difficult to follow. Some have been followed for several 

 weeks. Measurements of the electrostatic capacity of these layers 

 show that with constant potential difference the capacity is probably 

 proportional to the area. 



Further, the rate of creep depends on the pressure, so that as the 

 acid descends in the tube it reaches regions of greater and greater 

 pressure, so that the motion is slower and slower. If we take a tube 

 small enough to make it possible to invert it without the mercury 

 escaping, the creep is very rapid, in some cases so rapid that it is 

 difficult to follow. 



It is easy then to account for the high value of the capacity of the 

 electrometer as used in the above experiments. The acid rises rapidly 

 for some distance in the tube and the wetted area in the conical tube 

 is many thousand times the area of the meniscus. 



Experiments show that if the mercury in the tube is the cathode, 

 the rate of creep is diminished by a potential difference applied to the 

 electrometer and increased if the mercury is the anode. But these 

 effects are small and do not explain the changes in capacities observed. 



> Clark. Trans. Roy. Soc. Can., XII, 51, 1918. 



