

Vescosity of Pitch-like Substances. 3098 
The rate at which the dissipation of strain energy takes 
place may be different in different substances. We have 
thus to consider a new property of the substance: the rate 
at which the strain energy is dissipated under specified 
conditions. 

The Viscosity of Soda-Glass at different Temperatures. 
A tube cf glass was used in these experiments which 
admitted the insertion down it of a thermoelectric junction, 
thus obtaining a ready means of measuring temperature. The 
whole was surrounded by a thick-walled iron tube which 
could be raised in temperature by a row of small gas-jets 
placed beneath. The bore of the iron tube was a little larger 
than the glass in order to allow the latter to turn freely. 
In the case of a tube the formula for the viscosity becomes 
BS 2T 
= 71 i 4\? 
where R, and R,are the external and internal radii respectively. 
Fie. 6. 



ES 
Es 

S 
a 


50 

20 


10 

Twist in DEGREES 
Oo 
0 yl, 200 300° 400 500 60070000900 .000 100 
SEconDS ‘100 1200 1300 1400 1500 1600 1700 1800 1900 2000 
The Viscosity of Glass. 
(Different values of the torque were used in the two cases.) 
The results are given in a table at the end, and in fig. 6 
are plotted the results for two experiments. 
