﻿472 M. G. Quincke on the Capillary Phenomena 



32. The beautiful experiment by Liidtge*, of making in Pla- 

 teau's wire frame-work a film figure of water or oil (liquid 1) 

 and causing it to be forced away by oil or soapy water (liquid 2), 

 so that the films consist now of the latter liquid, may be ex- 

 plained by the secondary currents above-mentioned and con- 

 nected with the spreading of liquid 2 in the interior of liquid 1. 



Liquid 2 spreads upon one surface of liquid 1, provided 

 a i2 >a i"~" a 2 > ^ r0 ^ s °ff tae °ther surface of liquid 1, which, as 

 regards the nature of its surface, has been unaltered, breaks 

 through this, and now forms a circular film, whose diameter gra- 

 dually increases, as the diameter of the lens-shaped drop of 

 water on mercury increased when oil was placed upon the boun- 

 dary of mercury and water (§ 27). In this latter experiment 

 also may be observed, under favourable circumstances, a perfo- 

 ration of the very flat lens-shaped drop of water or the formation 

 of a circular film of oil in the interior of a film of water on the 

 mercury. 



Similar phenomena are seen on the surface of water when 

 a drop of oil has been let fall upon it so as to be separated 

 into many small drops in the water. One portion of the oil 

 spreads itself out quickly, as was described above (§ 29), to 

 a thin skin of modified oil with a greater capillary constant or 

 tension of the surface than the original unchanged oil. If now 

 the specifically lighter drops of still unmodified oil ascend in 

 the specifically heavier water and break through the thin skin 

 of oil, they form circular films on the surface of the water, whose 

 diameters gradually increase until the influence of the water 

 has also sufficiently modified the capillary constants of this oil. 

 I should seek the cause of this phenomenon chiefly in the differ- 

 ence of the capillary constant of the free surface of the modified 

 from that of the unmodified oil. 



33. The decrease of the capillary constant or tension of surface 

 when a liquid 2 spreads on the open surface of a liquid 1 can 

 be proved by methods which differ from the above, and particu- 

 larly from those given in the first four Sections of this memoir. 



U water (liquid 1) be allowed to drop out of the end of a 

 vertical sharply cut glass tube of r radius, then the weight of 

 each drop will be = a . 2r7r. By placing a small quantity of 

 olive-oil or oil of turpentine (liquid 2) on the surface of the glass 

 tube, which will then spread itself out on the surface of the falling 

 drop, a will no longer remain =et v but become — a 12 + a 2 < * v 

 and the magnitude of the drop of water will considerably 

 diminish. As the oil is soon carried off by the falling drops 

 of water, the thickness of the coating of oil diminishes with the 

 time, becomes < 21 (than twice the radius of the sphere of action), 

 * Pogg. Ann. vol. cxxxvii. p. 465(1869). 



