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THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1952 



resonant frequency and resonant resistance of the crystal in a vacuum, 

 then introducing the solution to be measured, the change in the resonant 

 resistance ARe and the change in resonant frequency A/ are determined 

 by an electrical bridge. Several short cuts are possible if the mechanical 

 impedance is not too high. By measuring the capacity at a frequency 

 considerably higher than the crystal frequency, the resistance at reso- 

 nance and A/ can be obtained by changing the frequency and resistance 

 until a balance is obtained leaving the capacity unchanged. This method 

 has been used to measure viscosity, and a recent precision study at the 

 Franklin Institute has shown that it agrees with other methods to an 

 accuracy of well under a per cent. 



The torsional quartz crystal has been successfully used to measure 

 liquids having a viscosity up to 10 poise, but above this viscosity the 

 electrical resistance gets so high that it is hard to measure it since it is 

 shunted by the much smaller reactance of the static capacitance of the 

 crystal. A crystal of higher electromechanical coupling such as am- 





Fig. 2 — Cell and 80-kc cn-stal for shear viscosity and elasticitj^ measurements 

 of liquids. 



