458 Mr. A. Griffiths on Diffusive Convection. 



When the steady state has been attained, the quantity of 

 salt which passes in a second is a constant, and equals 



vAt + Ak 



3* 



Fiff. 3, 







$^$- 



-$$$^ 







— — _v 



^- — — 



If t is zero at the top of the tube, and T at the bottom of 

 the tube, the solution of the differential equation which 

 arises is 



a) 



or 



• T-(l-,- 



cL\' 

 "* 1 





vl 







1 p k 



t=T T . . . 



vh ' 



l-e~ k 







differentiating (1) and (2) 







St vT-t(l- 



t 



-e 





-bl- k . 



vL 



a k 





,B* 



(2) 



fr 



and substituting this value of ^in the expression vAt + Ak^, 

 we find for the quantity of substance which passes per second 



vAT 



1— e * 



