sorbed in limited quantity, like the majority of soluble substances But if instead of administering them separately dissolved in water, as was done in the physiological experiments, they are incorporated with a loose and humid soil, these salts react upon the calcareous matter almost always existing in the ground, and are transformed into carbonate of ammonia, which exerts undeniably a favorable influence upon vegetation. From these facts it may be presumed that the introduction of lime and marl is not merely to supply the defective calcareous element, but likewise a principle, carbonate of lime, which produces a particular action upon the manure, changing, through double decomposition, the unassimilable ammoniacal salts there present into a carbonate capable of being assimilated, which transmits to the plant the azote of the organic matter of the dung and the carbon contained in the calcareous rocks.

These reactions which go on between soluble salts and one that is insoluble under the peculiar conditions united in arable land, show that we must not always conclude as to what passes in the ground from phenomena observed in the laboratory of the chemist; and it is probable that by extending the study of these singular reactions to alkaline salts generally, we shall better understand the mode of action and utility of saline substances in agriculture. Thus, for example, the operation of common salt as a fertilizer is still very obscure. Many skilful husbandmen question its efficacy; nevertheless, when moderately employed it seems to do good. In plants growing on the sea-coast soda is found in a great measure combined with organic acids, and the chlorine deduced by analysis from their ashes is nowise proportional to the alkali they contain. The whole sodium does not enter the vegetable as a chloride, but very likely as carbonate of soda, and that in virtue of a reaction analogous to the one which calcareous matter has upon ammoniacal salts.

It is quite certain that chloride of sodium in solution is not affected by carbonate of lime; but then it was proved by Clouet that if into sand moistened with this same solution powdered chalk be put, and the mixture left in contact with air, an efflorescence of sesquicarbonate of soda ere long makes its appearance. Thus by the conjoint effect of capillarity and the carbonic acid of the atmosphere, common salt in the conditions above mentioned undergoes by contact with chalk a partial decomposition, of which the result is carbonate of soda, a salt, like carbonate of potash, most favorable to the growth of plants. Accordingly, in furnishing sea-salt to a soil sufficiently calcareous, we really enrich it with carbonate of soda. We moreover perceive that the same salt diffused through land devoid of carbonate of lime may not produce any fertilizing effect.

OF WATER.

Water is not only indispensable to the life of plants, but likewise promotes vegetation after the manner of a manure, on account of the saline or organic substances it generally holds in solution. Rain is the source of the soft waters which flow in rivers, spring from

the soil, or constitute lakes. Rain-water although nearly pure is not absolutely exempt from extraneous matters. The air, especially after continued drought, always holds dust in suspension; this yields to the rain by which it is precipitated, whatever soluble matter it may contain.

It is further ascertained by the experiments of Cavendish and Séguin, that whenever the electric spark traverses a humid mixture of oxygen and azote, nitric acid and nitrate of ammonia are produced. Now this frequently happens; and according to Professor Liebig storm-rain always contains nitric acid associated with lime or ammonia. Common rain seldom contains nitrates, merely faint traces of common salt.*

In river and spring-water there necessarily exists a larger amount of dissolved substances derived from the strata they pass through, varying in nature according to the geological structure of the locality. From old crystalline rocks, like granite, water issues sometimes so little impregnated with salts, as to be almost identical with distilled water; that, on the contrary, which rises from a calcareous or gypseous bed is always contaminated with salts of lime. Notwithstanding the minute quantity of saline or earthy ingredients in spring and river-waters, they are drinkable, and considered good when they are limpid, without odor, capable of dissolving soap, and fitted for vegetable cookery. These two last characters are essential, inasmuch as proving that the waters contain only infinitesimal quantities of soluble salts of lime.

The action of tests readily indicates the nature of the dissolved salts.

Water contains: sulphates or carbonates, if nitrate of barytes causes a precipitate; a sulphate, when the precipitate is not redissolved by the addition of nitric acid;

Chlorides, if it give with nitrate of silver a curdy precipitate, insoluble upon addition of nitric acid;

Lime, when rendered turbid by oxalate of ammonia ;

Magnesia, if when mixed with pure ammonia, and preserved in a closely stopped vial, a white flocculent deposite ensues. This test, however, is only applicable to water that has been boiled sufficiently long to expel all the carbonic acid in solution, and which would tend to hold any carbonate of lime dissolved. Carbonate of lime is separated from water by ammonia, after some hours, in the form of granular crystals, which adhere to the sides of the vessel.

In order to render the operation of tests more sensible, the bulk of the water may be reduced to a half or a fourth by evaporation. Besides fixed salts, river-water always contains those of ammonia, particularly the carbonate; this fact was first ascertained, relative to the Seine water, by M. Chevreul.† Subsequently, Professor Liebig has discovered the same ammoniacal salt in rain-water; and M. Hunefeld has proved, that spring-water likewise con

* Annales de Chimie, t. xxxv. 2e série.

† Chevreul, Annales de Chimie, t. lxxxii. p. 56.

tains it.* Lastly, M. Hermann has even determined quantitatively, carbonate of ammonia in the ferruginous waters of a turf-pit. The water of the Nile is not exempt from it, judging at least from the analysis of its mud. According to Regnault, 100 parts of this mud dried in the air contain:†

Chloride of sodium, sulphate of soda, and

carbonate of ammonia.. Organic matter.

1

Water..

9

10

The beautiful synthetic experiments of M. Dumas demonstrate that water is formed of:

When pure, it boils at a temperature of 212° F. under a barome tric pressure of 30 (29.921) inches. It congeals at 32° F.

All natural bodies dilate, augment in volume, by the action of Water is heat, and contract under diminution of temperature. amenable to this law between rather wide limits; it deviates, however, and presents an anomaly as it approaches congelation. As with all liquids, the density of water gradually increases in proportion as it cools, until its temperature is 39°.38 F. Setting out from this point the density diminishes, the liquid dilates more and more, so that at 32° it occupies nearly the same volume that it did at 49°. From this remarkable property, it results that during the most intense cold the stagnant water which covers the meadows rarely attains a lower temperature than 39°, whereby the organs of plants suffer no damage.

Let us suppose, in fact, that at the beginning of winter a sheet of stagnant water has a temperature of about 54°; in proportion as the liquid at the surface cools, it becomes denser, descends, and is immediately replaced by inferior layers, which rise in the ratio of their less density; but these new superior layers, subjected to the same There is refrigerating cause, contract and descend alternately. then established in the fluid molecules, movements of ascension and Let descent, of which the result is the cooling of the entire mass. us now admit that in virtue of this continued mingling of the cooled superior layers with those below, the temperature of the sheet of water is lowered to 39°.38; at this degree of the thermometer, the water acquires its maximum density; in parting with its heat it not only contracts no more, but becomes lighter. If then a body of stagnant water at a temperature of 39° is exposed to the chilling action of the atmosphere, the superior layer, far colder than the inferior, will no longer descend, since it will become lighter as its

temperature diminishes. Thus it is that the water of a pond or lake freezes at the surface, while it preserves beneath a temperature some degrees above 32°. In a situation where the temperature of the air was 29o, Davy found the thermometer indicate 43o in the herbage of an inundated meadow completely covered with ice.*

1 30

50

Water is always impregnated with atmospheric air, and a minute quantity of carbonic acid. Deprived of air, it is not agreeable to drink; it is even said, when long continued, to prove unwholesome if the dissolved gases are expelled by ebullition. River-water usually contains th in volume of air, and th carbonic acid. In springwater, the amount of the latter is sometimes far more considerable. The quantity and nature of saline ingredients in drinkable water vary much in an agricultural point of view, the study of the contained salts would certainly be useful. The waters which serve as drink to the cattle of a farm, introduce into the dung-heap all the matters which are dissolved or held in suspension. At Bechelbronn, for example, I find that more than 2 cwts. of alkaline salts get into the dung in this way every year. When a farmer has the choice of several waters for giving his cattle or irrigating his meadows, he will do well to select that which is richest in alkaline salts, and still good to drink. In the steppes of America, it is astonishing with what discernment the cattle choose waters for allaying their thirst, containing minute quantities of sulphate of soda or common salt.

I close these considerations with a tabular view of the most recent analyses. The quantities of salts put down have been deduced from 100,000 parts of water for drinking.

* Davy, Agricultural Chemistry, p. 352