of Gases and Molecular Force. 525 



investigation of the properties of mixed gases (viscosity, con- 

 ductivity, and characteristic equation), where the attraction 

 of unlike molecules would be an essential element in the 

 question. The experimental investigation of the properties 

 of mixed gases could also be extended with advantage. 



With regard to conduction, the kinetic theory of forceless, 

 smooth, spherical molecules leads to the result that in a first 

 approximation the thermal conductivity k='S2<drjmv 2 /?nT , 

 where mv 2 /2 is the mean kinetic energy of a molecule of 

 mass m at temperature T . But if in order to come nearer to 

 what must be the conditions of conduction in natural gases, 

 we assume that the natural molecules transmit the whole of 

 their molecular kinetic energy in the same proportion as 

 they would transmit their translator^" kinetic energy if they 

 were smooth spheres, then h = '826r)C, where c is the specific 

 heat of the gas at constant pressure. According to this 

 formula the effect of molecular force on conductivity is found 

 by putting for r\ the value obtained when molecular force is 

 allowed for. The temperature- variation of the conductivity 

 of only three gases has been thoroughly investigated, namely 

 of air, hydrogen, and C0 2 . The temperature-variation of c for 

 air and hydrogen is so small that within ordinary temperature- 

 ranges it can be neglected, but for C0 2 c 100 /c according to 

 E. Wiedemann is I'll, and according to Regnault 1*147 . 

 For these three gases the theoretical ratio of the conductivities 

 at 100° C. and 0° C. is calculable according to the relation 



&ioo __ £ioo ^ioo _ £ioo /373\* l + C/273 

 h " c V Q " c \21Sj 1 + 0/373' 



using for each the appropriate value of C already found, 

 namely 113 for air, 79 for hydrogen, and 277 for C0 2 , with 

 which we get : — 



Authority. Date. Air. Hydrogen. 00 2 . 



Theory 1893 1-268 1-243 1'50 or T55 



Winkelmann 1876 1-277 1-277 1*50 



Graetz 1881 1-185 1*160 1'22 



Winkelmann 1883 1-208 1-208 1*38 



Winkelmann 1886 1-206 1-206 1-366 



Schleiermacher 1888 1-289 1-275 1-548 



Eichhorn 1890 1-199 1-199 1-367 



Winkelmann 1891 1-190 1-175 1401 



It will be noticed that the theoretical numbers agree best 

 with Winkelmann' s determinations of 1876 and with Schleier- 

 macher's ; but Winkelmann, returning with great devotion 

 to these difficult measurements, obtains persistently smaller 



