OP ARTS AND SCIENCES. 13 



II. 



NOTE ON THE DEPENDENCE OF VISCOSITY ON 

 PRESSURE AND TEMPERATURE. 



By Carl Barus. 



Presented January 13, 1892. 

 Table of Contents. 



PAGE 



1. Historical 13 



2. The Material chosen 13 



3. Definitions 14 



4. Hardness 14 



5. Method of Work 14 



6. Volume Viscosity 15 



7. Viscosit} 7 and Pressure. Isotherms 15 



PAGE 



8. Viscosity and Temperature. Iso- 



piestics 16 



9. Conditions of Constant Viscosity. 



Isometrics 17 



10. Isothermal Flow through Tubes . 17 



11. Measurement of excessively high 



Pressure 18 



1. Historical. — In the following paragraphs, I endeavor to give 

 a preliminary account of what may he called the isotherinals, the 

 isopiestics, and the isometrics with respect to viscosity. Notwith- 

 standing the great geological importance* of these relations, nobody 

 has as yet attempted to represent them systematically. 



2. The Material chosen. — In order to obtain pronounced results 

 for the effect of pressure on viscosity, substances must be selected 

 on which temperature has a similarly obvious effect. For, in 

 addition to the direct access to the molecule which is beyond the 

 reach of pressure, temperature has the same marked influence on 

 the expansion mechanism per unit of volume increment as the 

 other agency. Hence liquids like marine glue, pitch, etc., which 

 change continuously from solid to liquid, and in which this change 

 takes place at an enormously rapid rate and is complete within 

 relatively few degrees, are especially available for the present 

 investigation. 



The following data refer to marine glue. Viscosity is considered 

 as a physical quality, and apart from such chemical considerations 

 as are introduced in passing from one body to another. 



* This will be indicated by Mr. Clarence King, for whom this work was done. 



