250 
REVIEW OF LEIEIG. 
Borage, the Chenopodia, and the Jerusalem arti¬ 
choke, owe their nitric salts merely to ammonia— 
an assertion by no means confirmed by the experi¬ 
ments of John. 
In a chapter like that “ On the Origin and As¬ 
similation of Nitrogen,” it was to be presumed 
that Leibig would have examined the form under 
which ammonia is conveyed to the plants. As 
almost all plants grow in black mould, the rela¬ 
tion existing between the atmospheric ammonia 
and the humus was to be examined—a topic in¬ 
teresting not only in a theoretical but practical 
point of view. But Leibig treats the matter very 
slightly, merely stating (p. 83) that humus stands 
in the same relation to ammonia as powdered 
charcoal, viz., condensing the ammonia. But we 
have seen already that humus can not be supplied 
by charcoal, and although the latter substance ab¬ 
sorbs ammonia even more forcibly than humus, 
yet plants will not prosper in it. This, therefore, 
does not corroborate Leibig’s assertion. The 
province of a true chemist, in this case, instead of 
being satisfied with the trivial fact that rotten 
wood absorbs ammonia, would have been rather 
to inquire whether these two substances will com¬ 
bine, and what combinations they will form. C. 
Sprengel and Mulder have lately asserted that hu¬ 
mus and ammonia will form combinations soluble 
in water; Saussure also found, in all sorts of hu¬ 
mus, a soluble nitrogenous extract, by which he 
explains the conveyance of nitrogen to plants. In¬ 
stead of making experiments, and without even 
taking notice of those of such men as the above, 
Leibig despatches the whole question with the 
assertion that the humic substances contained in 
black mould (Damm Ere) are entirely insoluble in 
water. 
The explanation of the action of gypsum on 
plants is connected by Leibig with the existence 
of carbonate of ammonia in the atmosphere. He 
assumes that gypsum is decomposed by the car¬ 
bonate of ammonia of the air; and he considers 
it, therefore, a means of fixing ammonia, and con¬ 
veying it to plants; and he adds that “ This is 
obvious from the evident action of gypsum on the 
growth of grasses, and by the increased luxuriance 
and fertility of meadows manured with gypsum.” 
This explanation (replies Dr. Mohl) is only true 
in a chemical, but not in a physiological point of 
view ; because it is well known that gypsum is 
most beneficial to leguminous plants. But if its 
action consisted in fixing ammonia, there is no 
reason why it should not act beneficially on all 
plants, especially on corn. And although Leibig 
asserts the latter to be the fact, (Am. d. Chem. u. 
Pharm. xli. p. 369,) yet the farmers, who are 
pretty good judges in these matters, will not agree 
with the Professor. If Leibig explains in a farther 
part of his work the manuring influence of burnt 
clay and oxyde of iron by their attraction of am¬ 
monia, an influence which (he says) could not 
have been previously understood, it is certainly 
not to him that the discovery is owing, but to 
Sprengel, who in his “ Doctrine of Manures” has 
also explained the influence of such substances by 
their attraction of ammonia. 
Of the fifth chapter, headed “ The Inorganic 
Constituents of Plants,” Dr. Mohl says, that Lei¬ 
big justly rejects the prevailing opinion, that the 
salts absorbed by plants act merely as stimulants, 
and is right in considering the bases absorbed from 
the soil as necessary constituents of vegetation. 
Leibig says, that all plants contain vegetable acids, 
which become combined with inorganic bases (or 
organic, formed by the plants themselves) into 
neutral or acid salts; that, considering the con¬ 
stant presence of these acids, we have to infer that 
they serve some vital purpose, and that their for¬ 
mation constitutes some necessary part of the vital 
process. Hence, Leibig arrives at the conclusion, 
that several earthy or alkaline bases can be sub¬ 
stituted for each other in the vital process, and 
that the quantity of the saline bases absorbed by 
plants depends on the saturating capacity of the 
acids they contain. This (says Dr. Mohl) is the 
second new and important principle contained in 
Leibig’s work. Still, it can not be considered as 
perfectly evident, for it is only supported by the 
analysis of two plants. Whether the enigma 
which still shrouds the absorption of inorganic 
substances has been thus solved Dr. M. thinks 
doubtful. This theory, he says, is, in this respect, 
one-sided—that it regards only the basal propor¬ 
tion of earth and alkali, and neglects the consider¬ 
ation of the specific proportion, which appertains 
to such substances in a lesser or greater degree. 
Many facts show that the replacing of one base by 
another is only possible to a certain extent; that, 
moreover, the same quantity of a certain base, 
which may be absolutely required for the prosperi¬ 
ty of one plant, may act as a poison to another, &c. 
In this respect, lime more especially is conspicu¬ 
ous, as the flora of the calcareous Alps, compared 
with that of primitive rocks, clearly proves. In 
this respect some plants are very fastidious, and 
will only bear one certain sort of soil, while others 
grow in both. In the species which may be 
called fastidious of soil, the substitution of one 
base for another can not be supposed to take 
place. 
In a subsequent part of his book, Dr. Mohl ex¬ 
amines what Leibig has stated or retracted in his 
late work, “ Organic Chemistry in its Relation to 
the Doctrines of Dr. Grubes and Sprengel.” Dr. 
Mohl considers the explanations of Leibig in that 
place only as additional proofs of his inconsistency, 
and another sample of the uncertain style of his 
writings, “ which leaves the reader, on almost 
every important topic, in perfect uncertainty what 
it really is that Leibig means.” In only one in¬ 
stance, concludes Dr. Mohl, the author has spoken 
plainly; viz., in alluding to silica, of which he 
says that it is the first solid substance that is taken 
up by plants, and is that, moreover, whence the 
formation of wood takes its origin; acting, there¬ 
fore, like one of those particles of a solution on 
which the first crystals are formed, and that in 
Equisetum and the Bamboo silica assumes the 
form and functions of the wood. This theory Dr. 
Mohl calls a physiological blunder, (as it certainly 
is,) proving Professor Leibig;’s absolute ignorance 
of everything connected with the physiology of 
plants. 
(To be Continued.) 
