385 



This point is very essential, since the whole evasion of carbonic 

 acid depends on the surplus tension in the very surface of the 

 water. The difference found on different days in the open part 

 of the lake amounts to 2 and would therefore, if maintained 

 throughout the year, account for a yearly deposition in the lake 

 of about 6000 tons of lime. I have some reason to believe, 

 however, that the figure found is a minimum, or very nearly 

 so, because the weather during the investigation was exceedingly 

 favourable to the assimilation of the vegetable plankton. 



As seen by the first entries in the table the tension in 

 shallow creeks with abundant vegetation may be somewhat 

 lower, but still it is higher than that of the atmosphere. 



The tension is found to increase pretty regularly with the 

 depth. This is only what we must expect when the carbonic 

 acid is chiefly set free at the bottom and removed through 

 the surface. 



It appears from the above that lakes will act to a great 

 extent as decalcifiers on the water that flows slowly through 

 them, but the phenomenon no doubt deserves to be more 

 thoroughly studied, and I am of opinion that quantitative results 

 of some importance with regard to the deposition of lime could 

 be obtained by series of tension- and alkalinity-determinations 

 comprising at least a whole year. 



In rivers and brooks the conditions are far more compli- 

 cated than in lakes, because the water is continuously renewed 

 and also because organic material as well as particles of lime, 

 when such are formed, are carried away by the stream and 

 deposited elsewhere, perhaps in a lake or perhaps in the sea. 

 As 1 have but very few observations at my disposal I shall not 

 enter upon any discussion on these points but will only mention 

 the fact that the tension in a river, with an abundant vegetation 

 of Potamogeton, Ulva and other plants, is extremely variable 

 and may sink far below that of the atmosphere as will be seen 

 from the following analyses: 



XXVI. 25 



