Composition of Waters of Land-Drainage and of Rain. 145 



from their connection with other subjects which have lately 

 attracted so much attention. If we are to believe these figures 

 (and my own faith in them, founded on the care which has been 

 bestowed upon the analysis, is complete) we must at once con- 

 clude that the various estimates which have been formed for the 

 last two or three years on the quantities of ammonia and nitric 

 acid in rain are totally erroneous. We have been under the im- 

 pression that this quantity might very fairly be held to account 

 for the natural fertility of an unmanured soil. M. Barral's ex- 

 periments in Paris first gave rise to this impression, and an 

 examination of the rain falling at Pusey, by myself, seemed to 

 confirm his results.* It seems now, however, that the methods 

 of analysis for nitric acid were defective, and that no reliance 

 can be placed either upon such analyses or the conclusion drawn 

 from them. In point of fact the quantity of nitric acid brought 

 down by rain, instead of being much greater than the ammonia, is 

 actually far less, and the total quantity of nitrogen in either form 

 does not, as we see, exceed 6| lbs. in the wliole year. This 

 quantity is equal to 8 lbs. of ammonia, and would be furnished 

 by o5i lbs. of sulphate of ammonia, or 47 lbs. of guano. We 

 can hardly, therefore, with these facts before us, continue to 

 believe that the rain brings down nitrogen enough to account for 

 a normal or natural fertility, or the growth of 14 to 17 bushels of 

 wheat from year to year. 



I fear too that we must abandon the pleasant notion that the 

 refreshing effect of an April shower is due to these compounds of 

 nitrogen, since the rain of the whole month only contributes 

 1000 grains of this element, equal to about 1 lb. of guano to 

 each acre of land. 



It must not be supposed that I mean to deny that the ammonia 

 and nitric acid in the air are all-important agents in vegetation, 

 or that they are sufficient, without recourse to the doctrine of 

 the assimilation by plants of free nitrogen, to account for all the 

 phenomena observed. What I do mean, and what I have fre- 

 quently before said is — that we must seek elsewhere for the 

 measure of this influence, that the rain-water does not form a 

 trustworthy guide, and tliat it is in the air rather than in the 

 water that we shall find the chief quantity of these fertilizing 

 agents. The rain falls at certain periods only ; in the intervals 

 the nitric arid and ammonia are not accumulating, they are 

 removed by vegetation and by the influence of the soil. I 



* I regret that this analysis should have been published — at all events, without 

 the caution which, in my Report upon it, I reconiniemled Mitli re^zard to the 

 ado]ition of the fifjurcs. I was perfVctly aware of the unsatisfactory cliaracter 

 of tlie methiids which I employed, although they were the best then existing. 

 VOL. XVII. L 



