MECHANICAL PROPERTIES OF POLYMERS 



129 



Fig. 3 — Photograph of torsional ciystai ami I'c^d 



monium dihydrogen phosphate (ADP) will cause the electrical resistance 

 component to be smaller in comparison to the reactance of the static 

 capacitance and hence can be used to measure higher viscosities. How- 

 ever, since wires cannot be soldered to the surface but must be glued, 

 the crystal is much more fragile than quartz and its use has been aban- 

 doned in favor of another method which makes use of the phase and 

 attenuation change in a torsional wave in a rod caused by the surround- 

 ing liciuid whose properties are to be measured. 



This method, devised by one of the writers, consists in sending a short 

 train of torsional waves, periodically repeated, down a glass or metal 

 rod. As shown by Fig. 3, the torsional wave is generated by a torsional 

 quartz crystal soldered or glued to the end of the rod. These waves 

 tra\'el to the free end of the rod and are reflected back to the crystal 

 where they are detected, amplified, and displayed on a cathode ray 



^ This method is described by H. J. McSkimin, in a paper before the Ac- 

 oustical Soc. of Am. in October, 1951. 



