Surfaces, Clean and Contaminated. 399 



and before the above paper was written I had already at- 

 tempted to examine this point. The experiment, however, 

 did not succeed. The camphorated water had decidedly too 

 much tension (wave-number 14*7 instead of 15*5), but on the 

 other hand the liquid was clearly not saturated, inasmuch as 

 fresh camphor scrapings were lively upon an expanded surface. 

 I have recently returned to the subject with water which has 

 stood in contact with excess of camphor for more than a 

 month. 



Sept. 15. Fresh clean water. Expanded 13*7, 13*7. Motes 

 still. Olive-oil added, 15'2, 15'2 ; camphor fragments mode- 

 rately active. More oil, 15*3, 15*3; camphor nearly dead. 

 More oil, 15*5, 15*5 ; camphor dead. Fragments of camphor 

 and motes quite still. 



The saturated solution of camphor was now substituted. 

 Surface expanded ; 15*5, 15*5. Expanded, 15*5. This number 

 could not be reduced by any number of expansions of the 

 surface. 



It was observed that the surface was usually in motion, as 

 evidenced by an irregular drift of motes and camphor frag- 

 ments. The latter had no individual motion, all neighbouring 

 particles moving together. The effect is probably due to 

 local evaporation of camphor and accompanying increase of 

 tension. Associated with this was a fluctuation backwards 

 and forwards of the number of waves, such as was never 

 observed with pure or simply greasy water. 



We are thus justified in the conclusion that saturated 

 solution of camphor has the same tension as is found for 

 greasy water when camphor fragments are just dead. When 

 the saturated solution was diluted with about an equal 

 volume of water, the wave-number was reduced to 14' 7. In 

 these experiments the distance between the points was 9*20 

 centim., and the frequency was 42*12, so that the observations 

 are directly comparable with those in the example calculated 

 at length. 



The comparison of tensions for clean and camphorated 

 water may also be effected by the method of capillary 

 heights. Some observations by Mr. Gordon gave the follow- 

 ing:— 



Clean water 7-94, 7'91, 7'92 



Water changed 7'92, 7-90, 7'90 



Saturated camphor 5*63, 5*68, 5*65 



Clean water 7-97, 7*90, 7'92 



Water changed 7'94, 7-96, 7'93 



Saturated camphor 5*62, 5*63, 5'66 



2 E 2 



