Mineral Manures and Manuring. 283 
(containing 40T) grains soluble phosphate) dissolved in 1^ pint 
of water. 
Containing — 
In 24 hours 
precipitated of 
the Dissolved 
Phosphates. 
A red loamy soil 
Oxides of iron and alumina .. 
C-10\ 
1-22/ 
Grains. 
94. • 9Q 
A calcareous soil 
Oxides of iron and alumina .. 
7-54\ 
67-50/ 
31-40 
A stiff clay subsoil .. 
Oxides of iron and alumina . . 
17-3S\ 
1-02/ 
19-30 
A stiff clay surface soil . . 
Oxides of iron and alumina . . 
7-85\ 
2 08/ 
20-70 
A light saud soil 
Oxides of iron and alumina .. 
12-lGl 
0-15/ 
21-46 
Professor Nessler made like experiments with a loamy soil 
containing 18 per cent, of lime, tjut used 3-4 times as much 
superphosphate as Voelcker ; nevertheless he obtained similar 
results. 
Thus it has been clearly demonstrated that the value of super- 
phosphate as a phosphatic manure does not depend upon the 
solubility of the phosphoric acid, but upon the greater division 
of the insoluble phosphates which are produced from it by 
precipitation in the soil. The precipitates so formed are com- 
pounds which the roots of plants can easily absorb or at least 
decompose. This latter action must take place with the pre- 
cipitates of iron and alumina, for although iron has some 
application in the economy of plants, alumina is only found in 
a few exceptional families. That the precipitates of iron can 
be decomposed by the roots of plants has been directly proved 
by Dr. Peterson, both by means of water-culture and by field- 
experiments. 
The above experiments of Voelcker and Nessler show that 
1000 lbs. of earth can precipitate from 2 to 9 lbs. of superphos- 
phate. A high manuring, therefore, of from 4 to 5 cwts. of rich 
superphosphate per acre, would cause the phosphoric acid to be 
precipitated like a galvanic coating on the particles of lime, 
alumina, and oxide of iron of the surface soil, to a depth of 
from 4 to 9 inches. 
The diffusion and solution of phosphoric acid by means of 
the water in the soil are extraordinarily slight. My analyses 
of the surface and subsoils of experimental plots at Rothamsted, 
which plots had received yearly for 22 years 3J cwts. of super- 
