Coal ash also contains very minute quantities of alkaline salts, which usually escape analysis when they are not especially inquired after. One specimen analyzed in my laboratory, gave nearly 00.1 of alkali. Coal-ash is particularly useful on clayey soils; it acts by lessening the tenacity of the soil; and further, doubtless, by the introduction of certain useful principles, such as lime and alkaline salts. OF ALKALINE SALTS. It is impossible to doubt that salts having potash and soda for their base are useful in agriculture. The influence of wood-ashes, and of paring and burning is unquestionable; and they are so, in some considerable degree at least, in consequence of the salts of these bases which they supply, and which always enter into the constitution of vegetables. There are even certain crops which, in order to thrive, require a particular alkali; the vine, for example, the fruit of which contains bitartrate of potash, and sorrel, which contains the binoxalate of the same base, must needs have supplies of potash. The plants which are grown for the production of soda, the salsola, &c., from which barilla is made, must come in a soil that naturally contains a salt of soda, such as that of the sea-shore. It would appear, however, that the salts of soda or potash, must not exceed a very small proportion in the soil. All the experiments that have yet been undertaken with a view to ascertain the action of different saline substances on growing vegetables, have led to no very certain conclusion but this, that they must be used very sparingly. M. Lecoq has published an account of some experiments, made apparently with great care, which go to prove that common salt, in the dose of from 1 to 21 cwts. per acre, favored the growth of barley, wheat, lucern, and flax. Chloride of calcium and sulphate of soda, he also found to have the same good effects. M. de Dombasle, however, came to conclusions totally opposed to them, with reference especially to common salt, which, applied in the doses advised by M. Lecoq, was not found to produce any sensible effect. M. Puvis also obtained results that were equally negative. It would perhaps have been well had M. Lecoq begun by determining the proportion of alkaline salts which existed previously in the soil on which he conducted his experiments. If he operated on a soil that was either destitute of these salts, or that contained them only in minimum proportion, very probably he did good by adding them. Nitrate of potash has been repeatedly recommended as an agent useful in agriculture. The conclusions that have been come to, however, from its use, are far from accordant. In the processes or modes of using nitre to the soil, it is not uncommon to find it associated with soot, or with vegetable mould, substances which require no assistance of any kind to constitute them powerful manures, and the addition of which is therefore calculated to raise strong doubts of the advantageous qualities ascribed to nitre alone. Were the advantages of nitrate of potash much less questioned than they are, however, the high price of the salt would probably always oppose insuperable obstacles to its employment. This is the reason, in all likelihood that has turned the attention of English agriculturists, for several years past, to nitrate of soda, a salt that is imported in quantity from Peru, and of which the price per cwt. may be about forty shillings; a price which, were it found really useful, would permit of its being used. Admitting the accuracy of the experiments that have been made, indeed, we cannot doubt the efficacy of nitrate of soda on soil already furnished with organic manure. The quantity that has been recommended is about one cwt. per acre. Mr. Barclay made a few experiments after having heard much of the nitrate of soda from his neighbors, of the results of which the following examples will suffice to give a comparative estimate : Without nitrate. Wheat... ....31 bush. 2 pecks. With nitrate. 35 bush. 3 pecks. Difference in favor of 5 bush. 3 pecks. The produce of the land treated with nitrate, however, did not fetch so high a price at market as that grown without it; and every item of expense taken into the reckoning, the use of the nitrate was attended with no commercial benefit. Still this does not militate against the fact, that the production of vegetable matter was increased upon land treated with the nitrate of soda. And indeed much of the information which M. de Gourcy collected in England, is of a kind that tends to confirm the favorable influence of this salt on vegetation. Wheat, clover, and Swedish turnips are particularly specified as benefiting from its use. These facts admitted, we may ask how does the nitrate of soda act? The chemical constitution of the nitrates is such, that we might conceive their acting at once as mineral and as organic manures. The important point for solution was to ascertain whether the azote of the nitrate contributed in any way to the formation of the azotized principles of plants. Davy, in taking with much distrust the report of Sir Kenelm Digby's experiments on the influence of nitre in the cultivation of barley, shows no disinclination to believe that the azote of the salt may concur in the production of albumen and gluten.* This, however, is a point in physiology which may be put to the proof by experiment, and seems peculiarly worthy of being tested in this way. I have admitted it as extremely probable, that the azote of the azotized principles of plants has its source either in the ammonia, which is the special ultimate product of the organic manure we employ, or Agricultural Chemistry. in the azote of the atmosphere, or in both simultaneously; but the opinion which should maintain that the ammonia derived from the organic constituents of the soil, passes into the state of nitric acid before penetrating the tissues of plants, would find support nearly in the same facts which I have quoted as favoring the former view. We have seen, moreover, in our general considerations on nitrification, with what facility the azote of ammonia undergoes acidification in certain circumstances, a fact from which an argument of much potency for the nitric acid theory naturally flows. I shall here add an observation to which I have, up to this time perhaps, attached too little importance. When M. Rivero and I examined the hig! ly irritating and poisonous milky sap of the hura crepitans, we had oc casion to leave a considerable quantity of the water derived from the sap, after separating the caseum, to itself; by the spontaneous evaporation of this water, we collected really a considerable quantity of nitrate of potash. Since this time I have had occasion to note the same salt in the sap of several trees of the tropics. In the leaves and fruit, however, I have never found more than very minute quacities. Gypsum, sulphate of lime, or plaster of Paris, is a compound of 41.5 lime with 58.5 sulphuric acid; gypsum generally contains a quantity of constitutional water, in which case it consists of 79.2 sulphate of lime, and 20.8 water 100. This hydrate of sulphate of lime is one of the abundant minerals on the surface of the earth; it is met with in the crystalline state, and in granular and fibrous masses in the strata of most recent formation. It has no sensible taste, but is slightly soluble in water, this fluid dissolving of its weight of the salt. Exposed for some time to a white heat, it loses its water of constitution, and passes into the state in which when ground it is known under the name of plaster of Paris. 1 Gypsum is one of the most commonly employed of the mineral manures. Its virtues appear not to have been unknown to the ancients; but until lately its employment was limited to a few circumscribed districts. It was only about the middle of the eighteenth century that the protestant pastor, Mayer, took up the study of gypsum in the principality of Hohenlohe, proceeding upon certain information which he had obtained from Hehlen of Hanover, in the neighborhood of which, it was employed as an improver. By extending a knowledge of the virtues of gypsum, both by his example and his writings, Mayer did great service to agriculture. Experiments were soon instituted in all quarters. Tschiffeli in Switzerland, Schubart in Germany, and Franklin in America, wrote on its effects, or practically demonstrated them to the satisfaction of all. But it appears to be the fate all useful discoveries, of all happy applications of principles, to be opposed at first, and only to be admitted after having been vainly disputed. The use of gypsum soon aroused formidable opposition; and there is a curious episode in the history of the paper war that was long carried on upon subject, which I think worth noting. Among the most strenuous enemies of the use of gypsum, were the proprietors of the salt-pans. They declared that gypsum was not only incompetent to replace schlot or the refuse of their pans, as had been proposed, but that it was injurious; schlot was the only real improver, the stimulant of stimulants, for which there was no substitute. But it turned out by and by, that the schlot of the salt-pan was found to be neither more nor less than sulphate of lime, than gypsum-the article that was not only inefficient, but injurious. These gentlemen were afraid that the use of gypsum extending, they would want a market for their refuse. The use of gypsum once introduced, extended rapidly in France, particularly around Paris, whence it crossed the Atlantic, and the fields of North America were actually manured with the produce of the quarries of Montmartre. The lately cleared lands of America abound in humus, and the plants indigenous there were most beneficially acted on by gypsum, which really produced remarkable effects; in both the new and the old world, its power, as one of the most useful auxiliaries of vegetation, soon appeared to be established. We must not blind ourselves to the fact, however, that the partisans of gypsum were guilty of exaggeration. They spoke of the substance as a universal manure, capable of supplying the place of every other, as advantageous for every description of crop, as appli cable to every variety of soil. Experience soon set bounds to suck indiscriminate laudation; it was found that gypsum alone was inadequate to produce fertility, that it always required the concurrence of organic manures, if the soil did not contain them of itself; that it only acted beneficially on a certain, and that a very small number of plants; lastly, that it was upon artificial meadows, constituted by clover, lucern, and sainfoin, that it produced its best effects; its action, on the contrary, being scarcely perceptible upon natural meadows, doubtful in connection with hoed crops, and null with the cereals. These negative results cannot be called in question; they were come to by parties who were every way interested in having the decision otherwise. The best season for spreading gypsum is the spring, and when the clover, sainfoin, or lucern, has already made a certain degree of progress; calm and moist weather is the best for laying it on. Opinion was long divided as to whether it should be applied in its natural state, and simply ground, or first burned and then ground. But it is now generally admitted that burning adds nothing to the qualities of gypsum. Although the usual practice is to sow or powder the meadows with the ground gypsum, it is still acknowledged that good effects are obtained from incorporating the substance with the soil. The advantage of the practice of scattering it on in powder, so as to adhere to the wet leaves of the growing plants, I find explained in the equality of distribution which is by this means effected. In some places, the number and extent of which are by no means inconsiderable, no good effect whatever has attended the application of gypsum, although it has been administered in favorable conditions, and in connection with crops that elsewhere derive the highest amount of advantage from its use. This anomaly has been explained by assuming, without proving experimentally, however, that the fact is so, that the soil in these districts naturally contains a sufficient dose of gypsum. It has also been said that gypsum produces no effect on low-lying and damp soils. The quantity of gypsum employed in different places, varies greatly from 1 to 16 cwts. per acre have been recommended. The quality of the article employed has a great influence on this question, to say nothing of the price, which in many places is high. The opinions of practical men, with regard to the advantages and propriety of applying gypsum, although they agreed in certain determinate circumstances, were still far from being unanimous upon every point. A particular inquiry into the subject was therefore held worthy of its attention by the French government, and a comprehensive report on all the information collected, was made by M. Bosc to the Royal Central Agricultural Society of France. This report shows in a striking manner the advantage that may be derived from the lights of practical men; in a single line or sentence we frequently find a summary of twenty or thirty years of experience. It is, however, indispensable to go to these gentlemen for their information; the agriculturists who devote themselves to cultivation, it is notorious, write very little, and those who spend very little time in this way, on the contrary, write a great deal. It may be that the reason for the silence of the one, is that also for the eloquence of the other. The following series of questions and answers I believe to embrace most of the points connected with the employment of gypsum, that are of interest. 1st. Does plaster act favorably on artificial meadows? opinions given, 40 are in the affirmative; 3 in the negative. Of 43 2d. Does it act favorably on artificial meadows, the soil of which is very damp? Unanimously, no. Ten opinions given. 3d. Will it supply the place of organic manure, or of vegetable mould? i. e. will a barren soil be converted into a fertile one by the use of plaster? No, unanimously. Seven opinions given. 4th. Does gypsing sensibly increase the crops of the cereals? Of 32 opinions, 30 negative, 2 affirmative. The information thus obtained, valuable as it is, cannot yet be held to embrace every thing that seems desirable. Happily, all that was wanting has been supplied by the individual inquiries of Mr. Smith in England, and of M. de Villèle in France. The soil upon which Mr. Smith made his experiments was light, with a substrate of chalk; the vegetable earth was a yard in depth at the top of the field, and lessened gradually, in such a way that at bottom it was but three inches thick. Every precaution was taken that the respective breadths contrasted should be as nearly as possible in the same circumstances. The following table shows the results : |