184 



A still more accurate determination of the total amount of 

 solids in suspension in the river, both silt and plankton, is 

 afforded by the catches made by the Berkefeld army filter, 

 data concerning which will be found in Table XV. This filter 

 removes all of the suspended solids and permits their complete 

 removal from its surface, but adds a small portion of its own 

 substance to the catch. After the first few catches with this 

 filter the wear becomes somewhat uniform and is thus dis- 

 tributed. On computing the loss from the filtering sur- 

 face by wear, and quadrupling this volume to allow for its less 

 compact condition, we find that it constitutes less than five 

 per cent, of the catches washed from its surface. The true 

 amount of solids is thus about five per cent, less than the 

 figures cited in the tables and in the following discussion. 



The amount of water' strained in making these catches was 

 usually 5 liters, while the tables give the computed amount 

 per cubic meter. 



The amount of solids was measured by our usual method 

 of measuring plankton, that is, by condensation in a centrifuge. 

 In this treatment it usually attains the consistency of soft mud. 

 For the river the amount ranges from 148 cu. cm. (per cubic 

 meter), in declining water under the ice in December, to 5,416 cu. 

 cm., in the incipient stages of the winter flood of February 28, 

 1899. The average amount of the weekly catches for 1898 is 

 592.2 cu. cm. per cubic meter, which for an average flow of 

 24,600 cubic feet of water per second (see page 132) means a 

 discharge of 14.57 cu. ft. of solids per second, or, 459,794,232 

 cubic feet (1,301,990 cubic meters) per year, or 16,472 cu. ft. 

 (46.64 cu. meters) per square mile of the catchment-basin of 

 the river. 



The average amount, per cubic meter of water, of solids 

 taken at fortnightly intervals in 1898 in Quiver Lake was only 

 378 cu. cm., a fair index of the greater clearness of its waters. 

 In Thompson's Lake similar collections average 557 cu. cm., in- 

 dicating waters somewhat clearer than the river. In Phelps 

 Lake the average amount is large, 1,572 cu. cm., due in no small 



