DIFFUSION. 



In liquids D probably depends on the proportion of the ingredients of the 

 mixed medium u well as on the temperature. The dimensions of D are DT~\ 

 when L b the unit of length and T the unit of time. 



Tbd vduet of the coefficients of diffusion of several pairs of gases have 

 fopu j a fc enn i n ed by Loechmidt*. They are referred in the following table to 

 the centimetre and the second as units, for the temperature 0C. and the 

 of 76 centimetres of mercury. 



D 



Carbonic acid and air . . 0'1423 



Carbonic acid and hydrogen . . . 0'5558 



Oxygen and hydrogen . . . 07214 



Carbonic acid and oxygen .... 0'1409 



Carbonic acid and carbonic oxide . . 0'1406 



Carbonic acid and marsh gas . . . 0*1586 



Carbonic acid and nitrous oxide . . . 0'0983 



Sulphurous acid and hydrogen . . . 0'4800 



Oxygen and carbonic oxide . . . 0'1802 



Carbonic oxide and hydrogen . . . 0'6422 



Diffusion in Liquids. 



The nature of the motion of the molecules in liquids is less understood 

 than in' gases, but it is easy to see that if there is any irregular displacement 

 among the molecules in a mixed liquid, it must, on the whole, tend to cause 

 each component to pass from places where it forms a large proportion of the 

 mixture to places where it is less abundant. It is also manifest that any 

 relative motion of two constituents of the mixture will be opposed by a 

 resistance arising from the encounters between the molecules of these com- 

 |M>nents. The value of this resistance, however, depends, in liquids, on more 

 complicated conditions than in gases, and for the present we must regard it 

 as a function of all the physical properties of the mixture at the given place, 

 that is to say, its temperature and pressure, and the proportions of the 

 different components of the mixture. 



* Imperial Academy of Vienna, 10th March, 1870. 



