110 
INVESTIGATIONS ON ROTH A MSTED SOILS. 
Phosphoric Acid in Drainage Waters. 
Upward of thirty years ago the late Dr. Augustus Voelcker made 
analyses of several series of samples of the pipe-drainage waters col- 
lected from the Broadbalk wheat plats. The results were published 
in a paper " On the composition of waters of land drainage," referred 
to on p. 86, and was subsequently summarized in a Rothamsted 
paper, ' i On the amount and composition of the rain and drainage 
waters collected at Rothamsted." (See p. 49.) 
These are the only fairly complete mineral analyses that have been 
made of the drainage Avaters, although for many years constant deter- 
minations have been made of nitric nitrogen and chlorin. Averaging 
the various samples from each plat analyzed by Dr. Voelcker, we have 
the following results : 
Table 60. — Analyses of Broadbalk field drainage waters made by the late Dr. 
Augustus Voelcker, F. M. S. , 1866-1860. 
[Parts per million.] 
Annual manuring. 
Average 
quantity 
of phos- 
phoric acid 
in drain- 
age water. 
Plats 3 and 4 
Plat 10 
Plat 5 
Plat 7 
Plat 11 
Plat I.' 
Plat 13 
Plat H 
Unmanured 
Ammonium salts only 
Full mineral dressing without nitrogen 
Ammonium salts and full mineral dressing..- 
Ammonium salts and superphosphate 
Ammonium salts, superphosphate, and sodium suli>hate 
Ammonium salts, superphosphate, and potassium sulphate. 
Ammonium salts, superphosphate, and magnesium sulphate 
C. 03 
1.44 
.91 
.91 
1.66 
1.26 
1.09 
1.01 
If we assume a downward percolation of 10 inches of drainage 
water per annum, one part per million of water corresponds, in round 
numbers, to 2\ pounds per acre per annum. According to this esti- 
mate, the average variations in phosphoric acid Avashed away in the 
drainage waters, as shown in Dr. Voelcker's analyses, are from 1-J to 
3f pounds per acre per annum. 
To some extent the differences found bear a relation to the manur- 
ing and cropping conditions of the plats, but not altogether, and it is 
lo be remembered that the actual quantities analytically dealt with 
amounted only to small fractions of a grain of phosphoric acid per gal- 
lon of water; and furthermore, that the methods for the quantitative 
estimation of minute quantities of phosphoric acid thirty ySars ago 
were not quite so delicate as they are at t he present time. Too much 
Btress, therefore, must not be laid upon the quantitative differences 
Substantially, however, the results seem to show that no very apprel 
ciable quantity of manurial phosphoric acid passes away annually in 
the drainage water from the chemically manured plats, and that there 
is not a very meal difference between the quantity of phosphoric acid 
in the drainage water from the unmanured plats on the one hand and 
