140 Composition of Waters of Land-Drainape and of Rain. 



of April) that the drainage of the whole year on this particular 

 soil would as regards nitric acid be somewhere intermediate 

 between the two numbers above given — 11^ and 7^ — that is to 

 say, about 9 grains in the gallon. For the sake of illustration, 

 I will suppose that in this field of Mr. Paine the annual 

 liow of drainage water (240,479 gallons) carried off in each 

 gallon 9 grains of nitric acid ; we shall find that this quantity 

 is equal to 309 lbs. of nitric acid, which would be contained in 

 about 515 lbs. (or about 4^ cwt.) of commercial nitrate of soda, 

 Avorth, at its present price, about 4Z. Supposing, however, only 

 one grain of nitric acid to be removed in each gallon of water 

 for the whole drainage of the year, we shall have a quantity of 

 rather more than 34 lbs. 



Whilst we may assume that there is an indefinite but constant 

 loss to the soil in the shape of nitric acid, we find on the other 

 hand that the loss of ammonia, if calculated at its fullest, does 

 not exceed half a pound per acre in the drainage of the whole 

 year. This quantity is of course quite unimportant, and we 

 shall presently see that it is more than compensated by other 

 natural causes. 



The quantity of potash removed from a soil in the whole 

 drainage is also very insignificant. The largest quantity indi- 

 cated by the analyses is 0'22 (or about one-fifth of a grain) in 

 a gallon, which, on the previous calculation, would amount in 

 one instance (No. 6, Mr. Paine's sample) to about 7i lbs. in the 

 whole drainage of the year^this being, however, very much 

 larger than in any other of the specimens exhibited. 



It is to be remembered that as the drains are at a depth of 

 from 4 to 5 feet, all the soil to that depth is concerned in fur- 

 nishing the substances which we find in the water. Assuming 

 a superficial inch of soil, over an acre, to Aveigh 100 tons, and 

 that the drains lie at only 40 inches from the surface, we shall 

 have 4000 tons of soil, subject to the solvent action of the water ; 

 and . we shall find by calculation that the quantity of potash 

 removed from the soil in the year by drainage would be repre- 

 sented by the decimal '00001 per cent. — that is to say, that if the 

 whole of the soil were analysed before and after this quantity 

 (7 lbs. per acre) was removed, there would be found no greater 

 difference than the hundred-thousandth part of a grain in every 

 hundred grains of soil, supposing it possible, which it is not, for 

 analysis to detect it. Now, as there are probably very few 

 soils that would, on analysis, exhibit the presence of so little as 

 one-tenth per cent, of potash, it is plain that the drainage-water 

 would in effect remove only one part of ten thousand parts exist- 

 ing in the soil. It is only on a consideration of numbers and 

 quantity that we can appreciate some facts at their true worth ; 



