McLaughlin — CatapJwreds of Air-JBiibbles in Various Liquids. l5 



In broinobenzene, benzaldeliyde, aniline, cinnamic aldehyde, ethyl malonate, 

 and oleic acid, bubbles of diameters from O'OS to 0'28 mm. did not move under a 

 field of 95 volts per cm. 



Benzyl alcohol disintegrated under 95 volts per cm., but bubbles 0'08 mm. 

 and 0-12 mm. diameters showed no motion under a field of 14 volts per cm. 



Lactic acid likewise disintegrated, but a bubble 012 mm. diameter did not 

 move under field for thirty seconds prior to disintegration. 



In ethyl acetate bubbles grew, but this growth was uninfluenced by field. A 

 bubble 0'20 mm. diameter grew to 0-28 mm. while under observation for thirty 

 seconds each way with a field of 95 volts per cm., but showed no sign of motion. 

 Another bubble 0'16.mm. diameter was likewise uninfluenced by field. 



It was not found possible to trap an air-bubble in acetone and such volatile 

 liquids as carbon disulphide, but it was noticed that foreign matter moved to the 

 positive pole in impure acetone. 



Thus, in all pure organic liquids tested so far air-bubbles showed no cata- 

 phoresis. In one organic liquid, nitrohenzcne, air-bubbles never failed to move 

 under field. 'I'he first sample used was from ordinary laboratory supply, which 

 was a dark yellow in colour, due to oxidation from exposure to liglit. It had been 

 in store for some months. 



Bubbles 0-08 and 016 mm. diameters undoubtedly moved towards the negative 

 pole. Likewise, other samples from same source gave to air-bubbles a motion in 

 the same direction, the bubbles being of diameters 0-08, 016, 0'24, and 0-32 mm. 

 The latter moved 20 divisions per minute and 19 divisions per minute in opposite 

 directions under reversed fields of 95 volts per cm. A fresh pure distilled sample 

 of nitrobenzene was obtained. It was light yellow in colour, and was standing 

 for about ten days in a dark place prior to use. A potential of 95 volts per cm. 

 gave a motion of 4 divisions per minute in either direction, showing apparent 

 positive charge. A later observation showed a motion of 11 divisions per minute ; 

 the charge was still positive, but seemed to have increased. The bubbles were 

 0'20 and 012 mm. diameter, respectively. A second sample from the same source 

 gave to an air-bubble a negative charge, the motion being 3 divisions per minute 

 under the usual field. The same sample, after standing for three days in light, 

 again gave a negative charge to two bubbles of diameters 0"04 and 0'08 mm. ; the 

 charge had increased, the rate of motion now being 38 divisions per minute. Close 

 examination of the liquid showed that some traces of red rubber from the cork of 

 the bottle had got into it. A further sample of nitrobenzene was freshly dis- 

 tilled and carefully dried over phosphorus pentoxide. In all cases bubbles showed 

 an apparent positive charge. In the first sample bubbles of diameters 0'08, 012, 

 and 0'28 mm. all moved to the negative pole with velocity of 200 divisions per 

 minute under 95 volts per cm. In a second sample from the same source bubbles 

 of diameters 0'04 and 0-20 mm. moved towards the negative pole with a velocity 

 of 140 divisions per minute under the same field. A third sample gave exactly 

 the same motion to bubbles of 0'08 and 016 mm. diameters. In a fourth sample 

 two bubbles of diameters 0'08 and 012 mm. acted likewise. Thus, bubbles in 

 "pure" nitrobenzene move to the negative pole, but in impure nitrobenzene the 

 charge seems to depend, both in sign and magnitude, on the purity of the nitro- 

 benzene — a factor which is difficult to determine. 



Owing to the general absence of cataphoresis in the great number of liquids 

 tested, Quincke's statement that air-bubbles were positively charged in titrpentine 

 is of interest. On test, however, it could not be verified. Two distinct samples 

 of turpentine from two different sources were tested. In one an air-bubble of 



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