424 Prof. G. Quincke on the Edge-angle and 



plainly : hence liquids having minimum viscosity or maximum 

 fluidity, must exhibit, ceteris paribus, the most considerable 

 creeping. With this the facts appear, in general, to harmo- 

 nize ; for solutions of salammoniac, saltpetre, and potassium 

 chloride, liquids possessing great fluidity*, exhibit the pheno- 

 menon of creeping to a special degree. 



13. Demonstration of thin Liquid-films by Electric Dis- 

 charges. — In addition to the methods of the edge-angle and of 

 the phenomena of creeping, the existence of the thin liquid- 

 film near the flat drops of liquid upon a solid surface may be 

 proved by a third electrical method, provided the solid sub- 

 stance be an insulator {e. g. glass), and the liquid upon it be 

 a conductor of electricity. 



Two vertical platinum wires, P x and P 2 (Plate XIT. fig. 1 d), 

 of 0*138 millim. diameter, were ignited in a flame of pure 

 alcohol, and placed at 8 millims. distance from one another 

 upon a horizontal piece of plate glass of 60 millims. length 

 and 40 millims. breadth, which again lay upon a larger hori- 

 zontal piece of plate glass. At a certain time the wire P x was 

 connected to a charged gold-leaf electroscope by a long thin 

 silver wire ; the other wire, P 2 , leading to earth. 



Each platinum wire was fastened with shellac to the corner 

 of a triangle of plate-glass of 35 millims. width and 3 millims. 

 thickness. Each formed, along with two similarly fastened 

 plated copper wires, the leg of a little tripod 23 millims. high, 

 whose weight pressed it lightly against the surface to be in- 

 vestigated. 



With a seconds' watch, or a metronome beating half seconds, 

 the time t was estimated which was required for the gold 

 leaves 18 millims. long and 2 millims. broad, of an electroscope 

 to fall together from an angular separation of 60°. The same 

 experiment was then again repeated and the time t of the 

 discharge of the electroscope measured, after a flat drop of 

 water or saline solution had been deposited near the platinum 

 wires without touching them. Simultaneously the edge-angle 

 6 was measured by the method of reflexion (see § 3). 



It was found that t and r were greater or less according as 

 a longer or shorter time Z had elapsed since the cleansing of 

 the plate glass. But r was always much less than t , and in 

 general was only half as great as r . 



As examples I subjoin a series of such determinations, 

 where opposite each solution is stated in brackets whether 1, 

 or J, or J volume of the concentrated solution was contained 

 in 1 volume of the liquid employed. 



* 0. E. Meyer, Pogg. Ann. cxiii. p. 404 (1861) ; and Grotrian, Pogg. 

 Ann. clvii. p. 243 (1876). 



