minimum 



between Viscosity and Density in Fluids. 55 



with those of Andreef, found by a quite different method, it is 

 not likely that the differences are due to errors of observation. 



Respecting the viscosity, especially its connexion with the 

 density, the results are as follows : — 



I. Above the critical temperature, Gaseous Carbonic Acid. 



1. To the maximum of compressibility ( — r-j, i. e. to the 



s-f- 



of elasticity Is j^J, given by observation corresponds 



no minimum of viscosity, which much rather increases in a 

 constantly increasing ratio with increasing density. 



(~ and -j^ are always positive.) 



2. At the density <>1, about 500 times the normal, the 

 coefficient of friction exceeds the normal (0-000165 for 40 o- 3) 

 by only about 9 per cent, of the latter. 



3. At the temperatures 32°*6 and40 o, 3 the substance shows, 

 at equal density, slightly different values of \jl, very different 

 values of />. According to this the viscosity appears to he 

 much more simply connected with the density than with the 

 pressure. 



4. The influence of the temperature upon the viscosity, at 

 constant density, is so small that it cannot be inferred with 

 perfect certainty from observations embracing a temperature- 

 interval of only 8°. Since, however, the isotherm for 40 o, 3 

 runs entirely above that corresponding to 32°* 6, the viscosity 

 appears to increase slowly with the temperature when the 

 pressure is constant. 



II. Liquid Carbonic Acid. 



5. Liquid carbonic acid showed far less viscosity than any 

 other liquid hitherto examined. The friction-coefficient of 

 water, for example, at 15° is 14 # 6 times that of liquid carbonic 

 acid under the pressure of its saturated vapour. Even the 

 appearance of liquid carbonic acid enclosed in a glass tube 

 which is shaken excites the supposition that this substance 

 possesses very little viscosity. 



6. The viscosity of liquid carbonic acid at the temperature 

 of 25°'l increases with the density. By further extending 

 this investigation, and especially to other liquids also, we pur- 

 pose to ascertain the influence of temperature upon the visco- 

 sity of liquids at constant density — that is. the specific influ- 

 ence of temperature. 



7. At densities in the vicinity of 0'8 the isotherm correspond- 



