552 
On the Food of Plants. 
No. 4. — A rich black mould from Battersea Fields, in the Valley of 
the Thames. 
500 grains gave — 
Quartz sand .... 398 "2 grains. 
Finely-divided matter . . . 81 "0 „ 
Soluble prin-l organic . 1'6 grains, 
ciples . {inorganic* 0 • 8 „ 
. 2-4 „ 
Water H'l „ 
499-3 
Analysis of finely-divided matter : — 
25 grains gave — 
In 100 parls. 
Silica ..... 
13 
■1 
. 54' 
•8 
Alumina .... 
2 
•3 
9 
•2 
Oxide of iron 
2 
■G5 
. 10' 
•6 
Carbonate of lime , 
1- 
1 
4' 
•4 
Carbonate of magnesia . 
0 
■1 
0' 
•4 
Organic matter 
5' 
■0 , 
, 20- 
0 
Trace of insol. potash, and loss 
0 
■15 
0 
■6 
25- 
0 
100 
•0 
Abundance of phosphoric acid to be found; also ammoniacal salt. 
It is a very remarkable circumstance (already alluded to in the be- 
ginning of this paper), that strong, heavy clay soils, like the three hrst, 
should not contain more than 7 per cent, of alumina ; that this small 
quantity should confer on the soil so mucli plasticity and adhesiveness. 
It is probable, however, that the oxide of iron contributes largely to this 
effect in the cases cited. 
2. Analysis of Ashes of Plants. 
The processes adopted in the analyses, of which the results are given 
in the body of the essay, will l)e most easily rendered intelligible by an 
example. 
Analysis of the ashes of wheat, Battersea Fields : — 
Straw. — A portion of ash boiled in water and filtered. Solution 
neutral : gave no precipitate with carbonate of potash ; no indication 
of phosphate by magnesia test ; abundant white precipitate with chloride 
of barium, insoluble in nitric acid ; also some chloride with nitrate of 
silver. 
Portion of solution concentrated l)y evaporation, and mixed with 
solution of tartaric acid, gave, on agitation, abundant crystalline pre- 
cipitate. 
Matter insoluble in water treated with dilute hydrochloric acid, no 
perceptible effervescence, and only a small portion dissolved ; filtered 
solution evaporated to dryness, and acidulated water added. Insoluble 
matter almost inappreciable. To the solution ammonia added, which 
gave a precipitate of phosphates; filter: solution examined for lime 
* Chiefly sulphate of lime and common salt. 
