Section III, 1918 [51] Trans. R.S.C. 



• The Angle of Contact on Glass Made hy Mercury when Covered 

 with Another Liquid. 



By Dr. A. L. Clark, F.R.S.C. 



(Read May Meeting, 1918). 



Quincke^ has measured the angle of contact between mercury 

 and glass in air and has found that the value is about 148° for a freshly 

 prepared surface of mercury and clean glass, but is somewhat smaller 

 after a time. Pockels^ has measured the angle of contact between 

 glass and various liquids. Her success seems to depend on her method 

 of cleaning and testing the cleanliness of the glass. For many liquids 

 the angle made with glass is zero. 



Some experiments on mercury in glass tubes, when covered with 

 acidulated water, indicated that the angle of contact is, in many 

 cases, zero. Lippmann^ states that for pure water and mercury in 

 contact with glass, the angle is not zero, but for a H2SO4 solution, the 

 value drops to zero. Experiments had been undertaken to determine 

 the validity of the conclusion reached from study of such surfaces 

 before Lippmann's remark was noticed. No quantitative measure- 

 ments have been discovered, so the results are here recorded. 



A large drop of double distilled mercury was placed in a cleaned 

 watch-glass which rested on a steady platform. A spectrometer was 

 fastened to a rigid support with the axis horizontal and so arranged 

 that a small, silvered mirror mounted on its table was just above the 

 mercury drop. The light from a distant high-power tungsten lamp 

 fell on a large stationary mirror, placed higher up over the drop and 

 arranged so that a strong beam fell on the edge of the drop. A third 

 mirror, also stationary, placed below the apparatus, received the light 

 from the rotating mirror and reflected it through a small tube provided 

 with cross wires at each end. 



A cover glass cleaned in boiling HNO3, KOH, distilled water, 

 and finally by heating in the flame of a spirit lamp, was placed on top of 

 the drop of mercury and the light and mirror arranged so that the reflec- 

 tion of the light occurred at the boundary of the glass and the mercury. 

 The spectrometer reading was taken and then the small mirror rotated 

 till the reflection took place from the convex surface of the drop. The 



1 QuickC, Pogg. Ann. 105. Weid. Ann. 2, 152, 1877. 



2 Pockels, Phys. Zeit. XV, 39, 1914. 



^ Lippmann, Ann. de Chim. et Phys. (5), 494, 1875. 



