E. H. Richards 



335 



until its temperature had risen considerably^ as was the case in the 

 summer mornings, would lose oxygen owing to decrease in solubility. 



On the last point an experiment^ made by the author in DrMcGowan's 

 laboratory showed that good tap-water saturated with air at 7° C. could 

 be incubated for six days at 18*^ without appreciable loss of oxygen. It 

 was of course considerably supersaturated at the higher temperature, 

 but as long as the bottle is not shaken and no fermentation occurs there 

 is no appreciable loss of oxygen. 



In the experiment with rain one bottle to be kept at each tempera- 

 ture was tightly stoppered and the other had a layer of the same 

 paraffin, as used in the collection of samples, covering the water just 

 below the neck. This experiment gave the following figures: 



After 24 hours 



Dissolved oxygen in 

 parts per 100,000 

 Saturation (Dittmar) 



Dissolved oxygen. 



Parts per 10().00(» 



hy weiglit. 



1-5^ 



1-4 



1-3 



1-2 



11 



1-0 



0-9 



0-8 



At start 

 10° 



iTl 112 

 114 



at 14° 



at 25° 



Stoppered Paraffined 



1-11 M2 



1-05 



Stoppered Paraffined 



1-06 106 



0-85 



Jan. Feb. Mar. .\ijr. .Tuly Aug. Sept. Oet. Nov. Dec. 



Dissolved oxj'gen in distilled water saturated with air at temperature of 

 rain-water. 

 — Dissolved oxygen in rain-water. 



Fig. 1. 



^ Royal Commission on Sewage Disposal, 8tJi Report, vol. ii, Appendix, p. 9G (1913). 



