﻿462 M. G. Quincke on the Capillary Phenomena 



be drawn over to the other side, where the unchanged surface of 

 the mercury has the greater tension. 



If hyposulphite of soda be placed on the lens-shaped drop of 

 water, it contracts still more, since the capillary constant of the 

 common surface of mercury and hyposulphite of soda is greater 

 than the capillary constant of the common surface of mercury 

 and water. 



If the glass thread covered with oil is brought into contact with 

 the free surface of a lens-shaped drop of water on mercury, the 

 oil spreads on the water, diminishes the tension of its surface, 

 and the diameter of the drop increases. If at the same time the 

 glass thread wetted with oil be also, through immersion in the 

 water, brought into contact with the common bounding sur- 

 face of mercury and water, the oil spreads itself out upon it, 

 diminishes its tension (§ 14), and the drop of water assumes a 

 still greater diameter. 



If the quantity of oil placed on the free surface of the water 

 or on the surface bounded by the mercury is too great, the little 

 drops of oil slide on the surface covered with oil (compare § 29) 

 towards the periphery of the lens- shaped drop, spreads on the 

 free surface of the mercury, and with the diminished tension of 

 the latter the drop is observed to contract. 



It is well to remark that small quantities of oil placed on the 

 surface of a liquid x do not overstep the sharp edge of the lens- 

 shaped drop of water. The edge acts as the sharp-cut edge of 

 a vertical tube, in which the magnitude of the falling drop is 

 independent of the substance of the tube, or of the angle which 

 the liquid forms with the substance of the tube. 



By placing a greater quantity of oil on the free surface of the 

 water or of the mercury, the lens-shaped drop does not form a 

 sharp edge, the oil spreads itself over the entire surface, whilst a 

 skin of oil forces itself between the common surface of water and 

 mercury, and there arises a lens-shaped drop of water which is 

 arched strongly above and but slightly below. This form permits 

 the theory to be foreseen from the numbers of Table X. § 10, as 

 the cooperating tensions of the surfaces in the periphery of the 

 lens are : — 



a 13 =34-19 + &-76=37'95 milligrms., 



« 12 =34-19 + 2-10=36-29, „ 



« 23 = 2-10 + 3-76= 5-86. „ 



The upper portion of the liquid lens is nearly a hemisphere. 



In air mercury condenses the vapour contained in the at- 

 mosphere so rapidly, that only under particularly favourable 

 circumstances does a spreading of water on the free surface of 

 the mercury take place. Generally the water remains as a lens- 



