The Viscosity of Mixed Gases. 421 



than water. It would, therefore, increase both the sensitive- 

 ness of the calorimeter in measuring small quantities of heat 

 and the range of temperatures throughout which an investi- 

 gation might be carried. 



This calorimeter, as now made, enables the experimenter 

 of ordinary skill in manipulation to obtain results which 

 are comparable in accuracy and consistency with those 

 obtained by any calorimetric method in use ; ordinary care in 

 weighing and in reading the thermometers used being the 

 most important considerations to be observed. For these 

 reasons it is well calculated for student use as well as for 

 research-work, for which its wide range of application makes 

 it especially suitable. 



Physical Laboratory, Princeton College, 

 Princeton, N.J., U.S.A. 



XXXVII. The Viscosity of Mixed Gases. 

 By William Sutherland*. 



NEARLY fifty years ago Graham, in his beautiful expe- 

 riments on the motion of gases, encountered the fact 

 that by mixing a little hydrogen with carbonic dioxide the 

 mixture can be rendered more viscous than the carbonic 

 dioxide, although the hydrogen is less viscous than it. The 

 fact seems to have arrested his attention rather strongly ; for 

 he made a large number of experiments on the transpiration 

 of mixed gases through capillary tubes, with the result that, if 

 t x is the time of transpiration of a gas 1 under certain con- 

 ditions as to pressure and temperature, and t 2 the time for a 

 gas 2 under the same conditions, then for a mixture of n x 

 volumes of 1 with n 2 volumes of 2 the time t is in most cases 

 given with considerable accuracy by the empirical formula 



(ri! + n 2 ) t = ufa + n 2 t 2 ; 



but when hydrogen is one of the ingredients, the formula fails 

 entirely to represent facts. As the viscosity is proportional 

 to the time of transpiration, a similar empirical formula holds 

 for the viscosity of most mixtures, but fails for those contain- 

 ing hydrogen. This peculiar experimental fact also arrested 

 Maxwell's attention ; for in his Bakerian lecture in 1866, on 

 the viscosity of gases, he mentions it as a remarkable thing 

 that while hydrogen is only half as viscous as air, a mixture 

 of equal volumes of hydrogen and air is 15/16 as viscous as 

 air. Maxwell's measurements of viscosity were made with 



* Communicated by the Author. 



