u'o(> Drop-Weight Method for determining Surface- Tensions. 



Mr, Morgan says: — u Until surface-tensions,, which are 

 known to be accurate, are at hand, it must he assumed that it 

 is the fault of the values of this property that the method 

 which gives such precise results for the seventy liquids should 

 suddenly and inexplicably give less precise values for the 

 thirty Liquids which differ from them in no single property 

 which could affect the relationship."* 



But there is a property which could affect the relationship, 

 and that is the possible existence of a finite contact-angle 

 which may or may not vary with the temperature. This 

 would certainly affect the capillary-rise values, and in the 

 absence of any further knowledge it is more than likely that 

 its existence is just the reason for the sudden appearance of 

 the w * less precise values." 



If the difference be ascribed to this cause, it follows that 

 the drop-weight method must be assumed either to be inde- 

 pendent of the contact-angle, or to depend on some function 

 of # different from the cos 6 which governs capillary-rise. 

 As far as the figures go of which we have any present 

 knowledge, Mr. Morgan's value for ether differs both from 

 the capillary-rise values and from those values obtained by 

 methods which are independent of the contact-angle, as the 

 following table shows : — 



Temp. 1>0° 0. 



Morgan and Oann 16 % 13 dynes per cm. 



Ferguson (using Jaeger's method)... 17*30 



Ramsay and Shields T , 16*49 „ „ 



But too much stress should not be laid on solitary results 

 obtained by different investigators using different samples 

 of liquid. While it is quite true that a great deal of experi- 

 mental work remains to be done before the contact-angle 

 question can be solved satisfactorily, nevertheless a certain 

 amount of progress could be made fairly easily. As has 

 been shown above, it is very probable that turpentine and 

 ether have finite contact-angles ; if, therefore, Mr. Morgan 

 would add further to the debt which workers on surface- 

 tension phenomena owe to him for the many carefully 

 determined figures which he has already published, by 

 oivino- us figures for the surface-tensions of these two 

 liquids determined, on the same sample, by the drop-weight 

 method, the capillary-rise method, and any third method 

 which is independent of the contact-angle, the comparison 



• Journ. Amev. Choir.. Soc, June 1915. 

 t Surface-tension in absence of air. 



