CAPILLARY CONSTANTS AND THEIR 



MEASUREMENT 



By ALLAN FERGUSON, B.Sc.(Lond.) 

 Assistant Lecturer in Physics in the University College of North Wales, Bangor 



i. Classification of Methods for measuring Surface-tensions 



2. Critical Discussion of Principal Methods 



3. Discussion of Methods for measuring Contact-angles 



4. Conditions for Accurate Comparison of Capillary Constants 



of Related Liquids 



5. Surface-tension and Temperature 



The importance of an accurate knowledge of any physical 

 constant need not here be emphasised — the "fourth decimal 

 place " has from time to time proclaimed its weight with no 

 uncertain voice, and in a manner altogether disproportioned to 

 its relative magnitude. 



Amongst the physical constants of a substance in the liquid 

 phase, the surface-tension of a liquid is by no means the least 

 important. Inter alia, the information which it gives concerning 

 the state of molecular aggregation, and to a less degree the 

 chemical constitution of substances in the liquid state, renders 

 its accurate determination a matter of some moment alike to the 

 chemist and to the physicist. 



Nevertheless, in spite of the labour that has been spent on 

 these determinations and the many methods that have been 

 evolved, it cannot be said with certainty that the surface-tension 

 of, say, water is known with an accuracy of even 1 per cent. If 

 we restrict ourselves to those determinations which have been 

 carried out within the last twenty years, we find values given 

 for the surface-tension of water at 15 C. ranging between the 

 extreme limits of 71 and 77 dynes per centimetre, the majority 

 of the results grouping themselves round the values 71 to 75 

 dynes per centimetre. 



Whilst much of this variation is undoubtedly due to the diffi- 

 culties inherent in the formation of a perfectly uncontaminated 

 surface, it is no less true that the methods used are very variable 



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