CULTURAL CHEMISTRY. 
249 
the effective analysis of earths and soils, is the vast variety which exists, even at the 
slightest distances. As, for example, a pound of earth from a certain bed or plot, is 
sent to a chemist ; he subjects a given portion of it to the customary tests, enume- 
rates the results, tabularly, to the party, and states the deficiency or redundancy of 
one or other of the usual constituents. It is quite evident, that if every inch of the 
soil were precisely the same, analysis, accurately conducted, must be determinate in 
its results. But the fact is not so. In the same garden the constituents may and 
do differ in every particular, and in thousands of instances, to a most perplexing- 
extent. Hence, unless an entire plot, of very large dimensions, has been so 
laboured and comminuted as to bring the whole staple — soil and subsoil — to one 
homogeneous temperament, an analysis conducted by the most enlightened chemist 
must be unavailable to the practical cultivator. 
The mineral constituents of a soil, according to the sense adopted by Davy, 
Henry, and others, some five-and-thirty years ago, were then the chief constituents 
sought for. The vegetable, or organic and fibrous matters, were in the first instance 
separated by the sieve, or destroyed by a gradual and progressive combustion, and 
their quantity determined by loss of weight. Thus, in the 400 grains of earth 
analysed by Davy, according to the table at page 158 of his “ Elements,” 29 grains 
of vegetable fibre were detected. The cretaceous matter existing, as carbonate of 
lime, was separated by the action of muriatic iicid, which also dissolved some portion 
of the iron. These were precipitated by appropriate re-agents, washed, dried, and 
weighed. Sulphuric acid was next employed, to dissolve the alumina, and what 
oxide of iron was in the soil after the action of the muriatic acid. The earth 
remaining after the sulphuric acid was understood to be chiefly sand and fine silex. 
Davy observes, “ The method of analysis by sulphuric acid is sufficiently precise for 
all usual experiments ; ” and so it would be, were modern chemists satisfied by the 
mere detection of flint, clay, carbonate of lime, and iron ; but science now speaks a 
very different language, and aspires to higher pretensions. It has determined the 
great and important fact, that soil, to be available to the perfecting of ail vegetable 
productions, must contain at least the twelve following chemical constituents, eight 
of which have metallic bases, namely, silica, alumina, carbonate of lime, iron, in the 
form of protoxide, peroxide, or both, manganese, magnesia, potassa, and soda ; also 
three acids in combination with one or other of the preceding substances, namely, 
the sulphuric, hydrochloric, and phosphoric acids ; and finally some organic matters. 
Silica is the pure matter of flint and sand ; it consists of the metaloid silicium, com- 
bined with oxygen. iVlumina is an oxide of aluminum, but is never found pure in the 
earths. As silicious sands form the bulk of all fertile land, usually to the amount 
of 75 to 90 per cent., and even in stiff clays to half that quantity, so alumina confers 
adhesiveness and closeness of texture on soils. In clays, alumina exists to the 
extent of little more than 30 per cent., whereas only one-third of that quantity can 
be traced in 100 parts of a soft, unctuous loam : in some sandy earths it constitutes 
less than one hundredth part of their substance. Alumina gives temperament to 
VOL. XV. NO. CLXXIX. K K 
