station 1$8 . The mean depth at this station was 9-6 meters. Samples 

 were taken here on 10 date^; on five of these dates only surface samples 

 were taken. The data are shown in Table l6. Only minor differences were 

 found between the surface and bottom samples when both were taken. On dates 

 when both were not taken, the largest difference in temperature was 0.9$" C., 

 hence, it is probable that the chemical conditions were nearly uniform from 

 top to bottom during most of the s eason. Conditions here were essentially 

 like those at Station 37A, but differed from them in details, which might be 

 exoected from the fact that the two stations were not visited on the same dates. 

 In the discussion which follows, the notable differences will be pointed out. 



Oxygen content of the surface water ranged from 7.9 to 10.0 parts per 

 million. The smallest amount wac found on June 29, that is, at about the 

 same time as the marked decrease in oxygen at Station 37A. The decrease at 

 Station l58 was less outstanding than at Station 37A because the oxygen con- 

 tent on the preceding and following dates was rather low. Contrary to the 

 situation at Station 37A, oxygen approached nearest saturation in August. In 

 other respects the conditions at the two stations were similar. At no time 

 was there depletion of oxygen to the extent that it would be unfavorable to 

 organisms in the lake. The smallest amount present in the lower water was 

 7.8 parts per million, which was 86 per cent satiorated. 



An excess of free carbon dioxide was found only on May 21; on every 

 other date except October 22 there was a deficiengy.The amount ranged from 

 +1.2 to -2.6 parts per million. Seasonal changes in free carbon dioxide were 

 similar to those at Station 37 A. The principal difference is seen in the 

 changes in June; these were less pronounced at Station l58 than at Station 37A, 

 as was the case with oxygen. 



The pH values ranged from 7.8 to 8.2. The seasonal changes agreed, in 

 general, with those for free carbon dioxide. They differed from those at 

 Station 37A in the absence of a decrease in pH at the time of lowest oxygen 

 content. This difference might be expected from the less pronounced changes 

 in free carbon dioxide at Station 158. Another minor difference was that the 

 pH rose 0.1 unit higher at Station l58 than at Station 37A. 



Methyl orange alkalinity ranged from 89 to 98 parts per million, the same 

 range which was observed at Station 37A. The largest amount was found in early 

 August and the smallest in late September. Only minor differences were noted 

 between top and bottom samples. 



Station 8F . The mean depth at this station was 12.1 meters. Table 17 

 shows the data obtained here on eight dates in 1929. On three of these dates 

 samples were taken only at the surface, but in each case the top and bottom 

 temperatures were so nearly the same that it is reasonable to assume that chem- 

 ical conditions were nearly the same also. The data need not be discussed in 

 detail because they do not differ in important ways from those at Stations 37A 

 and l58. On two dates there were rather marked differences between surface and 

 bottom samples due to temporary stagnation of the lower water, but depletion of 



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