368 



Mr. H. A. McTaggart on 



organic compounds amongst which are the simpler alcohols 

 and fatty acids, to the second belong many inorganic salts. 

 The characteristic action of small concentrations of these two 

 classes of substances on the surface tension of water is 

 expressed in the law of Gribbs : — ( ' a small amount of dissolved 

 substance may lower the surface tension very much ; a small 

 amount can never raise it very much." In the case of 

 aqueous solutions of the alcohols and fatty acids — which are 

 known to lower the surface tension very rapidly — the surface 

 layers will be relatively rich in these substances and this will 

 be even more the case in very dilute solutions. It is to be 

 expected that solutions of this class would in cataphoresis 

 experiments show effects depending upon this property. 



In this paper the velocity of bubbles of air has been 

 examined in aqueous solutions of a number of alcohols, fatty 

 acids, &c, and in a few pure alcohols. The materials were 

 Kahlbaum's — in some cases redistilled — and the water used 

 was twice distilled, as explained in the last paper. The form 

 of rotating cell was the same as that previously described. 

 The results for solutions of the alcohols will be given first. 



In solutions of methyl alcohol it was soon found that the 

 velocity of a bubble of air depended upon its size, — an effect 

 which is not observed in pure water. If the solution is not 

 quite saturated with air, a bubble placed in it is gradually 

 absorbed, diminishing slowly in size till it vanishes. During 

 this process the velocity under a given fall of potential does 

 not remain constant as it does in pure water but varies in a 

 manner shown in the tables here given. The "time 3 ' here 

 and elsewhere in the paper is the time taken by a sphere of 

 air to move over 1 mm. and back again, i. <?., a distance of 

 2 mm. 



per cent. sol. CH 3 OH. 1 per cent. sol. C 2 H 5 OH. 



Diam. of 

 bubble. 



Time. 



Yolts/cm. 



"2 mm. 



28 sees. 



98 



•14 



32 





•12 



36 





•08 



34 





•06 



21 





•04 



13 





•02 



5 





Diam. of 

 bubble. 



Time. 



Volts/cm. 



•14mm. 



•10 



•08 



•04 



•02 



23 sees. 



20 



17 



14 



10 



38 



Two examples only are given, selected from a large number. 

 In nearly every such case the velocity increased as the size 



