Mr. A. Griffiths on Diffusive Convection. 455 



The pressure on the right-hand side of is given by the 

 equation 



P 2 =<7L 2 (l + J) + ^ Ll -L 2 )(l + T). 



P 2 is greater than P l5 the difference being equal to 



gT(Li-LJ 



2 



Since P 2 exceeds P l3 if the tap be opened liquid will flow 

 from the right to the left. 



If the tap be now closed, the diffusion will again attain a 

 steady state, and the same inequality of pressure will 

 be developed as before. The tap may again be opened and 

 so on. 



It is not necessary, however, to have a tap at C ; if there 

 is no obstacle whatever between B and N a steady flow will 

 take place down MN and up AB. 



The irregularity between AB and MN produces, as we 

 have seen, a pressure tending to produce circulation. On the 

 assumption that the density is the same at all points of a 

 horizontal layer, the magnitude of this pressure in dynes per 

 square centim. equals 



g^ d hi +^(L 1 -L S )(1 + T) -X" d it, 



where d is a function of the point under consideration in the 

 tube AB or MN. To find the nature of this function the 

 diffusion of copper sulphate, in a vertical tube, along which 

 the liquid is moving, must be studied. 



Section II. 



Diffusion of a salt in a vertical tube through which the liquid 

 is flowing with a. constant velocity, when the steady state 

 has been attained. 



Let I = distance of point from top of tube. 

 „ L = total length of tube. 

 „ A = sectional area of tube. 

 „ k = coefficient of diffusion. 

 „ t = quantity of dissolved salt per cub. centim. at a 



distance / from the top. 

 „ v = velocity of liquid up the tube. 



