DISSOLVED OXYGEN IN RAIN-WATER. 



By eric HANNAFORD RICHARDS. 



, (Rothamsted Experhnenfal Station.) 



From the agricultural point of view the amount of oxygen carried 

 into the soil as gas dissolved in rain has considerable interest. Since 

 all the oxygen required either for the bacterial activities of the soil or 

 for the root aeration of growing crops must first pass into the dissolved 

 state^ the supply of this essential element in a form immediately avail- 

 able must exercise a proportionately beneficial effect on the manufac- 

 ture of plant food or on the growing crop. Recent work on the decom- 

 position of organic matter in the soiF has shown that rainfall is one of 

 the chief factors controlling bacterial activity, but that its influence is 

 due to something more than the supply of water. The oxygen dissolved 

 in the rain appears to be the missing factor. As very httle systematic 

 work seems to have been done in this direction, estimations of dissolved 

 oxygen in rain at Rothamsted were made from time to time during the 

 year 1915. 



It is natural to suppose that rain should be saturated with dissolved 

 oxygen, the actual amount varying with the temperature at which the 

 rain was condensed. As it is difficult to determine this temperature the 

 comparatively few observers who have studied the gaseous content of 

 rain, have usually been content to record the volume of gas found and 

 the temperature of the rain-water when collected. 



As long ago as 1800 Senebier^ thought that sufficient attention had 

 not been paid to the quantity of oxygen gas contained in rain and 

 quotes Hassenfratz^ who had found more dissolved oxygen in rain- 

 water than in water from the Seine, concluding from this that rain-water 

 was more beneficial to plants than other waters. 



^ E. J. Russell and A. Appleyard, this Journal, 7, 1915, 24; also this vol. p. .385. 



2 Physiologie Vege'tale, vol. ui, p. 88, Geneva, 1800. 



* Hermbstadfs Archiv der Agriculiurchemie, vol. i (Berhn, 1804), p. 396. 



