On the Rain and Drainage - Waters at Rothamsted. 27 
the soil and crop, the sulphuric acid, chlorine, and soda appear 
in the drainage-waters in nearl}^ the same proportions as they 
exist in the manure, the crop taking up but little of these sub- 
stances, and the soil exerting little if any detaining power over 
them. Of the three diffusible substances just named, the sul- 
phuric acid is clearly the one most subject to appropriation. The 
crop of wheat on Plot 1 h, averaging G217 lbs. of total produce 
per acre in 20 years (1852-71), assimilated yearly about 0*4 lb. 
of soda, 8'9 lbs. of chlorine, and about 15 lbs. of sulphuric acid.* 
Soil has also apparently a greater retentive power for sulphuric 
acid than for chlorine. 
We have examples both in the analyses of Voelcker and 
Frankland of the alteration in the composition of drainage- 
waters at different periods of the same season. In Table XL. 
and in Table XLI. will be found analyses of waters collected 
from all the plots in January, and again in the middle or end 
of spring. The drainage-waters are naturally strongest soon 
after the application of the manures. As the whole of the 
manures (excepting the nitrate of sodium) were applied in 
October at the time to which these analyses refer, the winter 
drainage-waters are, in this case, the strongest. In spring the 
total solid matter dissolved in the water is seen to be much 
diminished, save in the case of Plot 9, which received a heavy 
dressing of nitrate of sodium in March. The diminution in 
strength as the season advances is greatest in the case of the 
plots most heavily manured, and is least in the water from the 
unmanured land. 
A nearer inspection of the figures shows that the spring waters 
are not only weaker, but of a different composition from those 
collected in winter. The dissolved matter of the spring waters 
contains as large a proportion of lime as the dissolved matter of 
the winter waters, and perhaps rather more magnesia, but the 
lime and magnesia are differently combined. The amount of 
nitric acid, sulphuric acid, and chlorine has greatly diminished 
since the winter, and the lime is now largely held in solution 
by carbonic acid ; the waters of the manured plots thus more 
nearly approach the waters from the unmanured plots in their 
composition. The chlorides seem to be washed out of the soil 
rather more speedily than the sulphates, which are often of less 
solubility, and for which, as already mentioned, the soil possesses 
a small chemical retentive power. The striking disappearance 
of the nitrates in spring is in part due to the active growth 
of the wheat-crop at this season ; we shall return to this part of 
the subject again. 
* The sulphuric acid assimilated is reckoned approximately from the total 
sulphur contained in the crop. 
