Measuring the Surface- Tension of Liquids, 

 Common Alcohol. 



401 



Plate. 



Platinum (1) 



Zinc 



Silver 



Tin 



Glass 



Platinum (2) 



Length 

 (centim.) 



6375 

 12-3065 



7-625 

 11-480 



5-044 

 13-481 



Thick 



ness 



(centim.) 



•0045 



•0105 



•0025 



•004 



•026 



•002 



TcosG 

 (dynes). 



23-38 



23-38 



23 52 

 2353 



23-56 

 23-57 



23-34 

 2334 



23-40 

 23-41 



23-37 

 2337 



Temp. C, 



15-80 



1590 

 15-92 



1600 



16-20 

 1624 



16-30 



16-43 



TcosG 

 at 16° C. 



23-36 

 23-36 



23-51 



23-52 



23-56 

 23-57 



2336 

 23-36 



23-43 

 23-44 



2340 

 23-40 



Variation 

 from 

 mean 

 of(l) 



and (2). 



-•02 

 -•02 



+•13 

 +•14 



+•18 

 +•19 



-02 



-•02 



+•05 

 +•06 



+ •02 

 + •02 



Error of 

 setting, 

 calcu- 

 lated. 



•02 dyne. 



•05 



•01 



•02 



•10 



01 



The zinc plate was slightly wedge-shaped and not very 

 regular on the edge. There was no such irregularity in the 

 silver plate ; but on watching closely I could see that the 

 alcohol crept rapidly up the plate, wetting it to a height of 

 several millimetres above the normal line of contact. Several 

 other trials with a silver plate showed the same peculiarity. 

 There may have been something similar happening on the 

 zinc plate, but if so I failed to detect it. Mica plates give 

 the same result as plates of platinum and glass. 



A platinum plate, if it can be obtained of the right thick- 

 ness, is most satisfactory for liquids like alcohol. But mica 

 makes a very good substitute. Mica can be split into sheets 

 10 or 15 centim. square and less than one hundredth of a 

 millimetre thick by a thin paper-knife under water. The 

 thin sheets may be floated upon sheets of paper, taken out 

 and left to dry. They are easily cut with the point of a sharp 

 knife when lying under a sharp-edged rule upon a glass plate; 

 but they require rather delicate handling at every stage. 



One of the difficulties of this method is caused by the ten- 

 dency of minute specks, if there be any on the liquid surface, 

 to gradually collect upon the plate and affect the measure- 

 ment more than they affect the tension of the whole surface. 

 A platinum plate should therefore be occasionally heated in 

 the Bunsen flame, and for this reason it is convenient to have 

 the plate in a metal holder. On a mica plate the effects of 



Phil Mag, S. 5, Vol. 36. No. 222. Nov, 1893. 2 E 



