﻿a Problem in Viscosity, 



1009 



the liquid by a given length of straight fine wire. I£ I is the 

 length of the film, / the force required to break it, then 



f 

 7 = \y . Fig. 3 is a perspective view of this apparatus, 



which was mounted above the viscosimeter. 



A platinum wire frame of the form shown served to pull 

 the film from the liquid, the horns remaining beneath the 

 surface of the liquid until the film broke. This was attached 

 to one end of a light aluminium pointer supported in a 

 metal frame by a torsion wire as shown. This acted as a 

 balance for measuring the force required to break the film. 



Fio-. 3. 



Torsion Wire 



The metal frame could be rotated about an axis through A, 

 thereby raising the platinum w^ire frame from the surface of 

 the liquid until the film broke. The reading of the pointer 

 could be noted at the moment of breaking and the equivalent 

 force determined by means of a small scale-pan and weights 

 attached to the pointer in place of the wire frame. 



The restoring force of the torsion wire could be supple- 

 mented by means of a rider attached to the aluminium 

 pointer, so that for a wide range of surface "tensions the 

 reading at the break-point could be brought on the 

 scale. 



