PROGRESS IN PHYSICAL CHEMISTRY. 233 



stants at any one value of the slope are the same as at any 

 other. Results of such a general character have not vet 

 been obtained by the use of other comparable temperatures, 

 and suggest the use of temperatures of equal slope in the 

 case of other properties, especially if these, like viscosity, 

 are largely affected by temperature. 



De Haas (29) has measured the viscosity coefficient 

 of methyl chloride between its boiling-point and critical 

 temperature, and Kamerlingh Onnes (30) has used the 

 values obtained together with those of Warburg and Babo 

 on carbon dioxide to test his theory that corresponding 

 states are to be considered as mechanically similar forms of 

 motion. According to this theory, at corresponding 

 temperatures, for two liquids A and B 



where M, 6, and it are respectively the molecular weight, 

 critical temperature, and critical pressure. Near the 

 critical temperature the theory is justified. The theory also 

 indicates that if 9 be the critical molecular volume, 

 riVlp 2 I VMQ and riZfn* / M 3 should be constants at corre- 

 sponding temperatures. Using the values for v given by 

 Pribram and Handl and earlier observers, this is found to 

 be approximately true for some forty liquids at the tem- 

 perature of "58. The acids and the alcohols especially give 

 large deviations. 



Vollmer (31) has tested the rule that at the boiling-point 

 the product of the heat of vaporisation and the molecular 

 volume is proportional to the square root of the viscosity 

 coefficient. For water, methyl and ethyl alcohols, this seems 

 to be the case, but ether and benzene give large deviations 

 of opposite signs. 



The viscosity of fused sulphur has been studied by 

 Brunhes and Dussy (32). It diminishes up to a temperature 

 between 156° and 157°, then increases, and at 162° is so 

 large that the substance could not be made to flow through 

 the capillary tube employed. 



Refraction and dispersion. — In connection with refraction 

 and dispersion the most extensive research is that of Bruhl 



