ON IM.AN I' COMPOSITION AND MANI IMAL K I'J^I' I IJK.MENTS. 145 
These (luantities are far from bein.i^ unimportant. A cubic metre of 
peat-moukl, indeed, weighing 582 kilos., has produced in this special 
case, in 111) days, 12-4 gr. of soluble nitrogen for a total quantity of 
2,620 gr. Maurepas leaf-mould. Total nitrogen 4-70 per 1,000. 
Nitiitic-iition per day and per kil > ()-00()Sl. 
1 cubic metre of this soil, weighing GGO kilos, and containing 8,102 gr. 
nitrogen, has produced in 117 days G2*50 gr. of nitrogen immediately 
utilisable by plants. Hot-bed soil of Versailles, total nitrogen 20 per 
1,000. 
Nitritication per clay and per kilo. .... 0 004G;i. 
This quantity corresponds to the solubilisation of 1*7 gr. of organic 
nitrogen per kilo, of soil per annum. It is seen, therefore, how the 
capacity for nitrification — that is to say, the production of utilisable 
nitrogen — varies in different soils. It should be remarked that in the 
majority of cases, horticultural soils being rich in leaf-mould and poor in 
lime, the nitrification decreases progressively until it becomes nil. When 
the lime-salts have disappeared, our leaf-mould soils acquire a particular 
appearance well known to gardeners^ They become pasty, water pene- 
trates with difficulty, aeration becomes a nullity, and then the plant-roots 
perish. The remedy is to mix with such soil a pretty large proportion of 
coarse sand and to aerate it as much as possible. We have also found, 
as the result of many experiments, that these soils can be again rendered 
fit for nitrification by watering them with weak solutions of carbonate of 
potash. Laboratory experiences have shown that the production of 
nitric nitrogen, which, without carbonate of potash, was for peat-mould 
0*00012 gr. per day and per kilo., was raised to 0*0219 gr. by a solution 
of 4*5 per cent, of carbonate of potash. Beyond this limit the nitrifica- 
tion has, on the contrary, diminished. The solution giving the best 
results for leaf-mould soils is 1^ per cent. It would not, however, in 
practice be safe for plants to reach these figures. We consider, even, that 
for watering plants in peat-soil it would not be prudent to employ solutions 
stronger than those of i^^ro- The experiments of 1899 regarding the 
forms under which nitrogen is best absorbed by the roots of plants have 
shown us that it was nitrate of ammonia which was by far the most 
rapidly utilised ; next followed sulphate of ammonia, then nitrate of soda, 
nitrate of magnesia, nitrate of potash, and nitrate of lime. 
Potash. — Potash is generally less abundant than lime in deposits of 
arable soil : it is, however, found more abundantly than nitrogen or 
phosphoric acid. We have already seen that potash arises from the 
action of water charged with carbonic acid upon the bisilicates of 
alumina and potash, which are themselves formed by the disintegration of 
feldspathic rocks (orthose). The potash in the soil is therefore almost 
entirely locked up in insoluble compounds, some of a mineral nature, such 
as the silicates ; and some in organic forms. Among these latter, some 
appear to be true salts, nearly insoluble, whilst others represent semi- 
soluble combinations, furnished by the association of a salt, mineral 
or organic, only soluble with a complex organic principle, often of colloid 
nature. At present no precise line of demarcation can be chemically 
determined betw^een the amount of potash immediately utilisable by the 
