54 
can become the food of plants." But the manures thus 
rendered soluble in water also unite chemically with 
certain portions of the soil, and thus become partially- 
insoluble by water : indeed, if this was not the case, by 
continued rains in warm weather, fields lately manured 
would soon be exhausted of their nutrition, and no 
food would be left for the ensuing crop. The vegetable 
substance thus rendered insoluble w^as first examined 
by Klaproth, and called ulmic acid ; by Berzelius it was 
called apotheme; and by Thaer humus. Malagutti's 
formula of the composition of ulmic acid is : 
30 Atoms of Carbon 22.5 or per cent. 57.15 
15 of Hydrogen 1.875 4.76 
15 of Oxygen... 15.0 38.09 
39.375 100.00 
Ulmic acid is alluded to by Sir H. Davy, though not 
by name, in these words : — " In most of the black and 
brown vegetable moulds, the earths seem to be in 
combination with a peculiar extractive matter afforded 
during the decomposition of vegetables. This is slowly 
taken up or extracted from the earths by water, and 
appears to constitute a prime cause of fertility in soils.'* 
It has been examined by Saussure and Braconnot,''^ and 
is said to have a great affinity for alumina; it also 
combines with lime, and forms an ulmate of lime ; but a 
great desideratum is to know whether it combines with 
impalpable silica and the proportions of its combinations 
with the earths. (Caustic potass, and the alkaline 
* Analysis of Mould by Saussure. 
Mould. Oak Tree. 
Carburetted Hydrogen Gas 124 116 
Carbonic Acid 34 29 
AVater containing Pyrolegnate of Ammonia 53 80 
Empyreumatic Oil 10 13 
Charcoal 51 414 
Ashes 8 0^ 
Mould contains more charcoal, and also more ammonia, and 
therefore more azote than the Oak from which it was derived, 42.5 
is the atomic weight of ulmic acid. 
