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Sulphuric and Phosphoric Acids.-Sulphuric acid is a combination of three parts of oxygen gas, two parts of sulphur by weight. Phosphoric acid is composed of about one and a half parts of phosphorus and one of oxygen, by weight. Sulphur is a well known substance. Phosphorus is contained in urine and other animal matter, is easily set on fire by friction, and is now in common use on friction matches.
Oxygen gas is one of the most important agents in the operations of nature. Mixed with azote, twenty one parts of oxygen, and seventy nine of azote, it forms atmospheric air.
Azote, or Nitrogen,—This gas, which is only mixed, not combined with oxygen in the atmosphere, combines also with oxygen in different proportions, forming nitrous acid, or aquafortis, nitric acid, &c. Substances, which, although composed of the same constituents as atmospheric air, are extremely acrid, corrosive, and destructive to both vegetable and animal matter, living or dead. Combined with chlorine, another gas, which I shall not now describe, it forms the most extraordinary and powerful explosive substance known. A single grain of it, (Troy weight,) is as much as any chemist dares to experiment upon. It explodes with prodigious violence when heated to 212°, the heat of boiling water, or, when touched by any oily or greasy substance. At present, we know of no use to which it is applied in the arts. But there can be but little doubt, it will at some future time become a more powerful agent of man than he has ever yet subdued to his despotic control. By its aid perhaps, mountains of rock may be crumbled to dust for agricultural or other purposes. Azote is a constituent part of animal matter. Its agency in the process of vegetation is not well known.
Oxygen one part, and hydrogen two parts, by measure, burned together produce water. Hydrogen is called inflammable air, is the lightest of all gases; with it balloons are inflated ; and combined with carbon is extensively used for lighting cities.
Carbon is the combustible part of charcoal, enters largely into mineral combinations, is a constituent part of all vegetables; and the most rare and valuable of all precious stones, the diamond, is pure carbon. Oxygen combines with all metals, and other inflammable or combustible substances, and forms a great variety of bodies called oxyds, oxyd of iron, oxyd of lead, &c.
The next ingredient or constituent of soils to be considered, is the salts. Salts are formed by the combination of acids with aļkalies, earths, and metallic oxyds. The salts most frequent in soils are the salts of lime, and iron, sulphate of lime, (plaster of paris) and phosphate of lime are found in all soils. The importance of all these constituents of soils may be inferred from the analysis of vegetables stated above.
The following table shews the quantity of earths and metallic oxyds, in grains, (Troy weight) obtained by Schræder from thirty two ounces of the seeds of the following kinds of corn:
13.2 15.6 66.7 144.42 152, * Carbonate of lime 12.6 13.4 24.8 33.75 46.2
magnesia 13.4 14.2 25.3 33.9 28.2 Alumina
0.6 1.4 4.2 4.5 3.2 Oxyd of manganese 5. 3.2 6.7 6.95 6.8 Oxyd of iron
2.5 0.9 3.8 4.5 2.4 Here we have a clue to the composition of soils best suited to the production of each of these kinds of grain. Here you see oats must take from the soil more than double the quantity of lime drawn from it by wheat. Of course it will be likely to be benefitted by a larger application of lime as a manure. But it should be known and remembered that every species of plant is endowed by nature with powers precisely adapted to its wants. If oats need more lime than wheat, the roots of oats have greater
* Probably phosphate of lime, and carbonate of lime. Other chemists have found in the ashes of oats, for instance, stalks and seed being burned together in 100 parts, silica 55, phosphate of lime 15, carbonate 5, potash 20, some oxyd of iron, &c.
power to decompose the earths that contain it, than those of wheat have. And as by reference to the annexed table of soils analyzed by Professor Hitchcock, it will be seen that all our soils contain a larger quantity of the sulphate and phosphate of lime, than any one crop of either of these kinds of grain contains, it may follow, that oats from their greater power of searching for, and more easily digesting it, will flourish better in a soil poor in its percentage of lime than wheat will in the same soil. And as the nourishment of plants is probably decomposed, cooked, or prepared, in some measure, by currents of galvanic electricity exterior to the roots themselves, a very important question is suggested for our contemplation in regard to mixed crops. May not the roots of one kind commingling with roots of another of stronger powers appropriate to themselves, in some measure, the food prepared for their neighbors? If so, it will account philosophically for what is considered a fact in some parts of our commonwealth, viz: that wheat does better sown mixed with oats, than it does alone. It will be seen by reference to the foregoing table, oats must have vastly greater power to decompose not only the salts of lime, but silica, alumina and oxyd of iron likewise. Here another thought occurs worthy of attention.
Will not agricultural chemistry by and by enable us to understand, by teaching us the analysis of vegetables, precisely how much one crop exhausts a soil of certain constituents more than another, and what must be restored to that soil to enable it to produce another crop of the same vegetable equal to the preceding. And also what other crops would be likely to do well on the same soil without the restoration of such constituents?
A still more important constituent of soils and vegetables, of which we have as yet only incidentally spoken is carbon. Carbon enters largely into a great variety of substances, mineral and vegetable, assumes every mode or form in which matter exists.
Solid in the diamond, in charcoal, and in its combinations with earths and metals; fluid in a great variety of liquids, and aeriform or gaseous in almost as many more. In every thing which can with strict propriety be named food for vegetables, it is the most important part. And vegetables have the power of decomposing most, if not all the compound substances of which it forms a part, and of appropriating the carbon to themselves. The most fertile soils contain the largest portion of carbon in combination with other substances, which combinations are usually either geine or the carbonate of earths and metals. Carbon 72.73 parts combined with 27.27 parts of oxygen, forms carbonic acid gas. This acid unites with earths and metals forming salts, called carbonates, carbonate of lime or marble, &c. Geine is a substance found in all soils, and its per centage may be considered as the best measure of their intrinsic value. It is decomposed vegetable matter, and of course contains the most important constituents of vegetables, the largest element.being carbon. I would here refer to the Essex Agricultural Society's Transactions for 1838, page 92, and 1839, page 35, for some account of this substance.
Geine, as there stated, exists in our soils in three states or conditions; soluble, insoluble, and combined with earths and metals, forming a class of bodies called geates. Soluble geine acts neither as acid nor alkali, but is converted into a substance having acid properties by the action of alkali, and in this state combines with earths, alkalies, and oxyds of metals, forming neutral salts, which may be called geates. They are all more soluble in water than solid geine, especially when they are first formed. The geates of the alkaline earths, lime, &c., are decomposed by carbonated alkalies. The geates of alumina and of metallic oxyds are soluble in caustic, or carbonated alkalies without decomposition. The geates of the alkaline earths by the action of the carbonic acid of the air become super geates (that is containing an
excess or a larger quantity of the acid or of that which possesses acid properties, than exists in neutral salts where the acids and the lime or other substances with which they are combined exactly balance or neutralize each other.) Super geates are always more soluble than neutral salts. Soluble geine includes the watery solution; the solid extract caused by the action of the air on the solution, and the combinations of this with alkalies, earths and oxyds. Insoluble includes all the other forms of this substance.
Geine forms the basis of the nourishing part of all vegetable manures. The relation of soils to heat and moisture depends chiefly on geine. Of all the problems to be solved by agricultural chemistry, none is of so great practical importance, as the determination of soluble and insoluble geine in soils. It lies at the foundation of all successful cultivation. Among the few facts best established in chemical agriculture are these; that a soil whose earthy part is composed wholly or chiefly of one earth, or any soil with excess of salts, is always barren; and that plants will grow in all soils destitute of geine, up to the period of fructification, failing of geine the fruit fails, the plants die. Earth, salts, and geine constitute then, all that is essential; and soils will be fertile in proportion of the last is mixed with the first. The salts can be varied but very little in their proportion without injury. The earths admit of a wide variety in their nature and proportions. The earths in our New England soils are chiefly the detritus of our primitive rocks, granite, gneiss, mica slate, sienite, and argillite. These earths are in fact all salts, formed by silica, which acts as an acid combined with alkalies, lime, magnesia, alumina, and metallic oxydes as bases.
In the analysis of soils for agricultural purposes it is not necessary to be more particular than to consider all these as one and the same thing, and call it granitic sand or silicates. All our soils, except per