364 
THE CULTIVATOR. 
ism of the plants from the phosphate of lime anil mag¬ 
nesia, because this mixture (guano and gypsum) con¬ 
tains less phosphate of potash or soda than the guano it¬ 
self; or, in certain proportions of gypsum, no alkaline 
phosphates at all; the soluble phosphates in the gua¬ 
no decomposing the gypsum into phosphate of lime 
and magnesia, and into sulphate of potash. I am far 
from asserting that we should not provide the fields 
with alkaline phosphates; the excellent effect of the 
guano, and of the human excrements, is too well known 
to question it, and we perceive, from this fact, that 
plants are in this respect like domestic animals which 
with a normal food, are healthy and strong, but do 
not fatten. On the contrary, we know that if we 
prepare the food of these animals artificially, so as to 
render it more easily digested and assimilated, they are 
enabled to consume, in a given time, a greater quantity 
of it by which all their parts increase in weight. The 
same happens with plants if we give them their nour¬ 
ishment in a state most appropriated for assimilation; 
their capability to attract the other elements from the 
atmosphere increases and their development is accelera¬ 
ted. If we recollect that the favorable effect of guano 
upon our fields depends on its amount of ammoniacal salts, 
of alkaline phosphates, and the other mineral constituents 
of the seeds, but that it is defective in alkalies, the prin¬ 
cipal elements of the herbs , straw, and roots, it is easily 
understood why the opinions of farmers, on the value of 
guano as a manure are so very different. On a soil, 
which is defective in alkalies, its effect is small; on a 
soil rich in them, it increases the produce in a remarka¬ 
ble degree; but, as I have already observed, the continued 
application of guano must gradually diminish the fertili¬ 
ty of our fields for a number of plants, because the ele¬ 
ments of those organs, of the leaves, stalks, roots, &c., 
without which the plants cannot be developed and can¬ 
not produce seeds, are taken off in the harvest without 
any restoration of them. I think it, therefore, certain, 
that the stable dung can replace the guano to a certain 
degree, but not vice versa. A rational agriculturist, in 
using guano, cannot dispense with stable dung. 
During my excursions in England, I have repeatedly 
directed the attention of the agriculturists, as Messrs. 
Pusey and Miles will, perhaps, recollect, to the neces¬ 
sity o r supplying the alkalies, and not merely the phos¬ 
phates and other salts; by a partial supply the equilibri¬ 
um of fertility is not restored, and if we supply guano 
alone, we do not act wisely, because we consume our 
capital by rich interests, and leave to our children an ex¬ 
hausted soil. 
And now, sir, the principles above-mentioned must 
guide us in the manufacture of an artificial manure. 
If they are neglected,—if the artificial manure is de¬ 
fective in one or two of the necessary elements,—the 
farmer in making use of it, will, in a very short time, 
discover the fact, by the injury he will have sustained 
from it. 
In the manufacture of an artificial manure, it must be 
kept in view, that the application of stable dung, of hu¬ 
man excrements, and of guano, is attended with a great 
loss, in consequence of the too great solubilty of their 
most efficacious elements, and this must be prevented by 
artificial means. This is evident, if we remember those 
countries from which guano is derived. It is known 
that the collection and preservation of the excrements 
on the African islands, and the coasts of Peru and Ohili, 
depend upon the scarcity of rain in those countries. The 
best sorts of guano contain in fact, more than one half 
of their weight of soluble salts, which, if exposed to the 
rain, are in exactly the same condition, as under similar 
conditions, a heap of salt. They dissolve in water, and 
are removed. Some months of rain would deprive those 
countries of all their riches. The remainder would 
have lost the greater part of its fertilizing power. Such 
effects, however, take place upon the guano with which 
our fields are manured. Only a small portion of its effi¬ 
cacious elements produce the beneficial effect they are 
capable of doing, the greater part being carried off' by 
the rain. The stable dung is, in this respect, in the same 
condition as guano; indeed, its principal elements are al¬ 
ready in a dissolved state, and, therefore, are carried off 
more easily than those of guano. 
A covering for those places in which stable dung is 
preserved, in order to shelter it from the effects of the 
rain, has been regarded in Germany as essential for 
preserving its manuring power. In consequence of the 
experience, that the soluble elements of stable dung are 
the most efficacious, it has in some cases, been drawn out 
with water, and it has been found advantageous to carry 
only this fluid to the fields. I need only refer to the fore¬ 
going analyses of the urine of animals in order to see 
upon which elements of it this effect depends. 
The reason why, in certain years, the influence of the 
best and most plentiful manuring is scarcely perceptible, 
is, that during the moist and rainy springs and summers, 
the phosphatse and other salts with alkaline bases, as also 
the soluble ammoniacal salts are entirely or partly removed. 
A great amount of rain and moisture removes in the 
greatest quantity, the very substances which are most 
indispensable to the plants at the time that they begin to 
form and mature seeds. The system of draining, which, 
of late has been so extensively followed in England, 
brings the land into the state of a great filter, through 
which the soluble alkalies are drawn off, in consequence 
of the percolation of rain; and it must, therefore, become 
more deficient in its soluble efficacious elements. 
Attentive farmers must have observed that after a 
certain time the quality of the grain on land laid dry 
according to this principle, deteriorates; that the pro¬ 
duce of grain bears no due proportion to the produce of 
straw. 
What is more evident, sir, after these remarks, than 
that intelligent farmers must strive to give to the soil 
the manuring substances in such a state, as to render pos¬ 
sible their acting favorably on the plants during the 
whole time of their growth. Art must find out the 
means of reducing the solubility of the manuring substan¬ 
ces to a certain limit, in a word of bringing them into 
the same state, in which they exist in a most fertile vir¬ 
gin soil, and in which they can be best assimilated by 
the plants. 
The whole attention of chemists should be directed to 
the attainment of this end. I am myself occupied with 
a series of experiments which lead me to hope that this 
problem can and will be solved. If it succeed, as I have 
no doubt it will, in combining the efficacious elements of 
manure in such a way as that they will not be washed 
away—their efficacy will be doubled; if in this manner 
the injurious consequences of the present system of drain¬ 
ing be removed, agriculture will be based upon as cer¬ 
tain principles as well aranged manufactories. Manu¬ 
factories of manure will be established, in which the 
farmer can obtain the most efficacious manure for all va¬ 
rieties of soils and plants. Then no artificial manure 
will be sold, whose exact amount of efficacious elements 
is not known, and this amount will be the scale for de¬ 
termining its value. In the application of such rational¬ 
ly compounded manures, the good will of the farmers 
must help bring them to perfection. If, then, by the 
united efforts of the manufacturer and the farmer the best 
proportions are ascertained, a new era will arrive in 
practical farming. Instead of the uncertainty of mere 
empiricism, all the operations of agriculture will be car¬ 
ried on with certainty, and instead of waiting the results 
of our labors with anxiety and doubt, our minds will be 
filled with patience and confidence. 
I am, sir, your obedient servant, 
Giessen, 1845. Dr. Justus Liebig. 
Frosts.— Prof. Kirtland. speaking of the softening in¬ 
fluence of bodies of water on frosty air, and particularly 
of Lake Erie, and of the Ohio river, says, “ For several 
years in succession, I have found from observation, that 
the Dahlias were killed in the same night at Cleve¬ 
land, and at Cincinnati, though they had been destroyed 
a month earlier in most of the counties intervening. 
Salt for plum trees. —Several persons speak of the 
efficacy of salt in causing fruitfulness in the plum tree, by 
repelling or destroying the curculio, as the result of 
actual experiment. 
