39 
CHEMISTRY OF SOILS AND MANURES. 
\AAAA/'/WWV > 
3-31 per cent, of organic matter, whilst in very inferior soils, which I have examined, the per centage 
amounted to 12-15 per cent. In corroboration of the former results, I may be allowed to state those 
of Dr. Anderson recently obtained in the analyses of some of the best wheat soils from different 
districts of Scotland, and published in the Scottish Journal of Agriculture, for July, 1850. 
Wheat soil 
5 ) 
Per centage of organic 
matter in soil. 
. . . 10-1981 
6- 3271 
7- 3625 
8- 5508 
4*5460 
3-4760 
6-670 
Per centage of organic 
matter in sub-soil. 
4- 8358 
5- 8554 
4-6932 
6- 8270 
3-7660 
Mid-Lothian, 
East Lothian, 
Renfrewshire, 
Perthshire, 
Morayshire 
Morayshire, wheat soil of a different description 
Berwickshire, Wheat soil . 
The organic matter is of a very complex composition, and owes its origin for the greater part to 
vegetable remains, as the roots, stems, &c., of former crops, and partly to animal matters, derived from 
the decay of insects, all added purposely in the form of manure to the land. 
The vegetable and animal remains, under the influence of water, air, and heat, gradually decay, 
producing a brownish or black powdery substance, or rather a mixture of substances, which are known 
to the practical gardener under the name of humus or vegetable mould. It is by no means a s im ple sub¬ 
stance, but it is composed of a great many organic acids and products .of vegetable decomposition. There 
are particularly two kinds of humus—brown and black—the first is contained in large quantities in the 
brown variety of peat; the latter, or black humus, the result of further decomposition of the brown, is 
found in black peat. The earthy brown or blackish substance deposited in the interior of hollow trees 
is the same complex substance commonly called humus. 
It is not my intention to enter into a minute description of the composition and chemical character 
of humus. Suffice it to mention the names of some of the vegetable acids which are found in the sub¬ 
stance called humus, by the practical man, viz.: ulmic, humic, crenic, apocrenic, and geic acids. 
These organic acids resemble each other very much in their general aspect, as well as in their composi¬ 
tion. Ulmic and humic acid may readily he extracted from peat,—the first from brown, the latter from 
black,—by boiling the powdered peat with a diluted solution of common soda of the shops. These 
acids enter into combination with the soda, forming a soluble dark brown coloured product, from which 
they are readily separated by an acid, which has a greater affinity for the soda than the vegetable 
acids. On the addition of muriatic acid, or spirits of salt, for instance, to the brown solution obtained 
by boiling peat with carbonate of soda, a dark brown or blackish-coloured, flaky, voluminous 
substance is separated, which, collected in a filter, washed and dried, constitutes a blackish, tasteless 
very hygroscopic substance, devoid of smell. Chemically speaking, this substance is a mixture of 
ulmic and humic acids,—ulmic acid prevailing if brown peat be used, humic acid if black peat. 
Humus and the other organic substances found in the soil play an important part in the processes 
of nutrition of plants. Perhaps too much importance has been attached by former naturalists, and by 
many practical men this is done to the present day. The fertility of a soil is estimated by them by 
the quantity of humus, which they regard as the only, or, at least, as the chief nourishment of plants. 
Recent researches, however, have shown distinctly the great influence which the inorganic matters 
exercise on the growth of plants, which inorganic substances are taken up by the roots, and discovered 
in the ashes of plants. It has further been proved experimentally that organic matters only are 
incapable of supplying all the wants of the growing plant, hut that every plant requires certain 
inorganic substances, which if not present in the soil will set a barrier to its healthy growth. The part 
humus plays in the nutrition of plants has been lately the subject of much discussion, and many contro¬ 
versies amongst chemists and physiologists. The most opposite opinions have been held out, volumes of 
papers have been written on this subject; the undeniable effects of humus on vegetation have been 
explained according to preconceived theories, and the efficacy of organic matter in the soil has even been 
denied altogether in spite of all practical experience. It would be unprofitable to the general reader to 
criticize all the different theories. There can be no doubt that humus supplies plants with food—whether 
with organic food alone, or inorganic likewise, or whether it exercises merely a beneficial influence on 
vegetation, in furnishing a continual source of carbonic acid, arising from its decomposition, or whether 
it acts likewise beneficially in condensing ammonia gas from the atmosphere we will not here discuss. 
TIumus certainly performs a most important part in the soil, and acts beneficially on vegetation in more 
than one way; for that reason all attempts to explain its functions by one action only must be unsatis¬ 
factory, and might lead the practical husbandman to serious errors in the management of the land. 
