383 



and we must evidently look for a cause which will not fix 

 carbonic acid in some form or other for a shorter or longer 

 period but will permanently displace it from the lake. This 

 cause can be no other than the diffusion of carbonic acid 

 which takes place between the water of the lake and the 

 atmosphere. 



In order to show that this cause is amply sufficient to 

 explain the formation of the lime-deposits in lakes I must 

 go into a small calculation. Bohr^) has defined as the evasion- 

 coefficient of a gas from a fluid that quantity which leaves the 

 fluid through 1 sq. cm. of the surface when the density of the 

 gas in the fluid is 1, that is to say, when 1 cc. of the fluid 

 holds absorbed 1 cc. of the gas. For carbonic acid in water 

 he has found the coefficient of evasion at 8° /9 = 0.108 and 

 the corresponding coefficient of absorption «=1.28. If we 

 take the surplus tension of carbonic acid in the water of a 

 lake to be only Vioooo (tension in the water 4 and in the atmo- 

 sphere 3) the active density will be Z> = 1.28 x 10"*, and the 

 quantity leaving during one year (T=5.25x 10^ minutes) and 

 1 sq. cm. 



Q = ßDT = 1.08 X 10-* X 1.28 X lO"' X 5.25 X 10^ = 7.25 CC. 



To this quantity will correspond a certain amount of 

 carbonate of lime deposited on each sq. cm. of the bottom, 

 depending upon the state of saturation of the water entering the 

 lake. The maximum amount will be 7.25 x 1.96 x 2.3 = SSmgrs.^), 



redissolved is however a very small quantity in most lakes and com- 

 pletely inadequate to account for the abundant deposits of lime. 



') Bohr: Definition und Methode zur Bestimmung der Invasions und- 

 Evasionscoefficienten bei der Auflösung von Gasen in Flüssigkeiten. 

 Werthe der genannten Constanten .... Ann. der Physik und Chemie. 

 Neue Folge Bd. GS. 1899, pp. 500—525. it is possible that the values 

 found by Bohr are somenthat too small. 



*) In this calculation no account is taken of the waves which will of 

 course greatly augment the surface and thereby also the evasion of 

 carbonic acid. 



I need hardly say that it is not my opinion that the whole of such 



