ox I'LAN'I" « I IMPOSITION ANI» MXM KIAL IfKCil l IJ K.MKNTS. 147 
afresh a double defoinposition wliir.'li ic-^^encrates sulphate of liin(>, and 
forms carbonate of potash. >s'ow, we have seen above what was the 
benelicial action of the carbonate of potash on nitrification, and also 
as a solvent of hunnis. The nitrification is an active agent in carrying 
away the lime in tlie efiiuent w^ater. The nitrate of lime which is formed 
by the saturation of the carbonate is extremely soluble ; by consulting 
the following- table which shows the respective quantities of lime and of 
humus contained in our horticultural soils it will be remarked that the pro- 
portion of lime annually carried away by nitrification is a matter of the 
greatest importance. It is necessary, therefore, in the case of soils which 
cannot be renewed, to introduce from time to time a little marl to main- 
tain their fertility : — 
Nitric nitrogen 
Lime carried 
Lime 
Humus 
produced per annum 
away j)er annum 
Soils. 
per l,nn(). 
pcrl,OUU. 
per kilogramme 
Uramines. 
per kilogramme 
Grammes. 
Hotbed Soil 
. G6-9o 
405-0 
1-689 
1-182 
English Loam . 
. 2-87 
86-00 
1-412 
0-988 
Leaf-mould 
. 1-77 
170-00 
0-295 
0-20() 
Trap Loam 
. 1-40 
3102 
0-105 
0-07H 
Peat -mould 
. 1-9:5 
188-00 
0-069 
0-048 
The physical condition of the lime in arable soil is of very great im- 
portance. It is always interesting when it is a question of a soil which 
contains a notable quantity of carbonate of lime to study the source, the 
nature, and the quality of the same. Analysis by the rapid process of 
M. Mondesir, that is to say, by attacking the soil with a weak organic 
acid, aflbrds a very good indication regarding the useful portion of the 
lime contained in the soil. 
Phosphoric Acid. —Phosphoric acid is certainly one of the principal 
elements of plant food. It often exists in very small proportions in our 
soils used in horticulture. The addition of small quantities of this 
element has the happiest results, especially as regards the formation of 
the reproductive organs, in which are found a mass of combinations of 
phosphoric acid with organic substances and magnesia. Its part is, 
therefore, a most important one from the point of view of fruit pro- 
duction. In the soil the phosphoric acid is met with either in the form 
of phosphates (some soluble in water, and others insoluble therein, but 
soluble in weak mineral acids), such as phosphate of lime, phosphate of 
sesquioxide of iron, alumina, and phosphate of magnesia, or under 
the form of ethereal compounds comparable to the glycerophosphates. 
Also under the form of very complex phospliorised organic compounds 
belonging to the order of phosphorised animal combinations, such as 
triethylphosphine. Plants can assimilate the phosphoric acid produced 
by the dissolution of various phosphates by water charged with carbonic 
acid, but a more important part is attributed to the portion of phosphoric 
acid derived from humic combinations. Following up the idea of 
M. Deherain, I have considered the amount of phosphoric acid which 
is dissolved by cold acetic acid as the amount immediately assimilable 
by the plant roots. In the following table we give the total phosphoric 
acid, that is to say, that which is soluble in boiling aqua regia, and the 
amount which we consider as assimilable which is soluble in cold acetic 
acid. This table shows that in our soils the addition of phosphoric acid 
