SUMMARY

Tags paper outlines a simple means for representing changes in the viscosity of liquids with changes in temperature, pressure and composition. It was found that, to a very good approximation, a certain function of absolute viscosity (or of kinematic viscosity) is linearly related to temperature, its reciprocal is linearly related to pressure, and that a linear mixture rule is applicable to such a function. Since the relations involved are linear, they may be treated by the simplest of graphical methods (using ordinary co-ordinate paper), or by the more precise analytical methods, which are in this case almost as simple as the graphical methods.

While linear equations are adequate for many purposes it is a simple matter, in dealing with very precise data, or very large ranges of temperature or pressure, to obtain greater accuracy by the use of additional terms, containing the second powers of t or p.

Designating the function by L when it refers to absolute viscosity and by L' when it refers to kinematic viscosity, it is defined by the equations 71 = AeBlz and alv = AeBIL. where n is viscosity, and v is specific volume, both in c.g.s. units; A and B are constants which are the same in the two equations. The numerical value of A is 5 X 10-' and that of B is 1000 log, 20.

Since the functions L and L' are intended to be working tools, it is necessary to have tables by means of which conversions from viscosity data, as usually reported, can be made conveniently. Tables for converting rl to L, or, lv to L' (one table serves both purposes) and for converting Saybolt seconds, Redwood seconds, or Engler degrees to L' are included in an appendix.

The process of using the tables and the new functions is illustrated by applications to some of the beat available data on change of viscosity of oils over wide ranges of temperature, pressure and composition. In problems of technical viscometry, it is shown that if values for an oil have been determined with one viscometer, such as the Saybolt, at two temperatures, Redwood or Engler values for the same oil, at their respective standard temperatures, can be correctly and easily determined by simple graphical or analytical methods.

While the paper presents a considerable amount of evidence that the use of the new functions offers a convenient means of dealing with problems in viscometry, their usefulness can be judged beat by actual trial.

INTRODUCTION

The purpose of this paper is to outline a simple means for representing changes in the viscosity of liquids with changes in temperature, pressure and composition. It was found that,. to a very good approximation, a certain function of absolute viscosity (or of kinematic viscosity) is linearly related to temperature, t, its reciprocal is linearly related to pressure, p, and that a linear mixture rule is applicable to such a function

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