THE CIIEMISTRY OF SOILS AND MANURES. 
which finally develope into spines, or become soft shoots ; the flowers are dioecious, minute, and appear 
in little bundles at the end of the non-developed buds. The drupe is red when ripe, ovate, acuminate, 
enveloping the nut by a four-cleft pulp, whose arms meet at the apex. The gum resin is collected in 
the cold season, by making incisions with a knife in the tree, letting the resin fall on the ground "■ 
hence its dirty and impure state as found in the shops. 
We conclude with Dr. Royle's remark: — "The whole of the species of this genus require to be 
carefully examined from good and authentic specimens, accompanied by their respective products," 
before the several doubts which obscure the matters we have been considering can be satisfactorily 
resolved. — M. 
THE CHEMISTKY OF SOILS AND MAMJEES. 
By Dr. A. Yoelcker, Professor of Chemistry in the Royal Agricultural College, Cirencester. 
INORGANIC MATTERS — POTASH, SODA, LIME, AND MAGNESIA. 
FROM what has been already stated, it appears that the incombustible portion of the soil of 
England, on an average, amounts to no less than about 96 per cent, of its whole weight, when 
free from water. In good garden land it constitutes about 90 per cent. The general composition of 
the earthy and incombustible part of the soil has already been indicated ; but though an acquaintance 
with the subject may furnish the gardener with valuable hints in choosing proper soil for the particu- 
lar plants he wishes to grow, yet such general ideas are insufficient for a clear understanding of the 
doctrine of manures, and guiding the practical man in economical operations. We are therefore not 
satisfied with having mentioned the names of the earthy matters in the soil, but shall now proceed to 
examine a little more in detail their exact chemical nature, the state of combination in which they occur 
in the soil, then physical and chemical properties, and their probable functions in relation to vegetable life. 
All fertile soils, besides organic matters, always contain a determinate quantity of ten or eleven 
different chemical substances. These, we have seen, are: — Potash, Soda, Lime, Magnesia, Alumina, 
Lon, Manganese, Silica, Sulphur, Phosphorus, and Chlorine. 
1. Potash. — When we burn the wood, smaller branches, or leaves of any of our indigenous trees, 
a whitish ash remains behind, amounting to 1 — 2 per cent, when wood has been used, whilst the smaller 
branches produce a larger quantity of ash, and the leaves as much as 6 or 7 per cent. ; this ash, washed 
with water, and the washings evaporated in an iron pot, and calcined, furnish the commercial pot-ashes. 
From these pot-ashes pearl-ash is obtained by adding a small quantity of water, decanting the liquid 
from the insoluble impurities present in crude pot-ashes, and evaporating to dryness. Pearl-ash, 
winch constitutes the residue, is an impure form of potash in combination with carbonic acid, or 
crude carbonate of potash. When a solution of carbonate of potash is boiled with newly-slaked 
quicklime, it is gradually deprived of carbonic acid, the latter entering into combination with the lime, 
and the carbonate of potash thus is converted into pure or caustic potash, as it is termed, on account of 
its effects on vegetable and animal substances. 
Potash, which never occurs in nature in this caustic state, in the hands of the chemist can be separated 
into a silver-white soft metallic substance — potassium ; and into a gaseous element — oxygen. Potash 
exists in considerable quantity in the ashes of all land plants — in some in larger, in others in smaller 
quantities. Many plants require, as a necessary article of food, a large amount of potash — for instance, 
the common Bracken (Ptcris aquilina) ; and as the soil is the only source from winch they are naturally 
supplied with potash, we are furnished at once with the explanation why this and other plants delight 
more in one soil than in another, and why the application of wood-ashes, which chiefly consist of 
carbonate of potash, promotes the healthy growth of Clover, Beans, Peas, Potatoes, and other plants 
whose ashes contain much potash. 
Carbonate of potash, however, is not the form in which potash is generally met with in soils. 
Potash constitutes but a small proportion of the whole mass of the soil, amounting seldom to more 
than 1 per cent., and often to a mere fraction per cent., and is found here chiefly in combination with 
silica. Such combinations, or silicates of potash, form part of many minerals. Some kinds of felspar, 
mica, and granite contain a large proportion of silicate of potash, amounting often to 15 — 20 per cent., 
and silicate of potash, though in much smaller quantities, also enters into the composition of many 
trap rocks, basalts, and whinstones. On the gradual crumbling down of the solid rock, silicate of 
potash is set free, and rendered available to the plants. Clays — which, as we shall see hereafter, are 
i principally derived from felspar — likewise invariably contain silicate of potash, and it is partly for 
c -Bi this reason that light land, generally deficient in potash, is benefited much by claying. 
