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It is among the interesting consequences, by which all minute researches into nature are at once rewarded and encouraged, that the pursuit of one object almost invariably leads to the unlooked-for discovery of others, -as the high road to a great city leads us past many mansions, opens up beautiful prospects, and brings us now and then to cross-roads where finger-posts indicate the way to places of which the very existence was previously unknown to us. The study of limestones, with a view to economical purposes only, would furnish us with instances in point. We will mention one of them, chiefly because of its close relation to the illustration we have already drawn from the mineral phosphates of the greensand and the crag.

In noticing these phosphates, we explained how essential they were for the production of bone in animals, and that to all plants they were a necessary of life; that therefore they must exist, to a certain extent, in the soil from which plants draw their mineral food; and that they constituted most valuable manures, accordingly, whenever any deficiency in respect of them had to be supplied.

Now in analysing limestones and burned lime, it has been discovered that a trace of this phosphate of lime exists in them all. In some it is merely a trace, in others it amounts to a sensible and practically useful proportion. One of the main benefits which follow from burning limestones and slaking burned lime is, that the lime itself, being naturally reduced, or falling to an impalpable powder, can not only be extensively spread over and minutely mixed up with the soil, but is in a condition, also, to act more readily upon those ingredients of the soil which it is intended to influence. Of this minute subdivision the mineral phosphate contained in the lime necessarily partakes, by which means it goes further than a larger quantity applied in the grosser form of bone-dust, or in any of the other forms in which it has hitherto been usually laid on the land.

In so far, therefore, as they contain phosphate of lime, applications of quick lime really act directly as manures; and since in some limes, even of the same geological age and position, this phosphate is six times more abundant than in others, we have arrived at an intelligible cause of the difference which different limes present, in the character of manures. To a soil naturally deficient in phosphates, and in districts where the artificial application of phosphates is unknown, the use of one of these limes rather than the other must be attended with important consequences.

Not only are such considerations economically useful to the practical man — in showing him how and what to select, and

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the relative money values of this or that variety - but they explain why in some places land will bear and pay for liming much longer than in others; why some soils remain long fertile without any artificial addition of phosphates; and how in some localities the rearing and breeding of stock, and the reaping of yearly corn, may be continued from generation to generation without apparent injury to the land.

One example, among the numerous perplexities of the farmer, we may venture to specify, as the statement we have just made enables us to explain it. Dairy husbandry has long prevailed in Cheshire. Now it has been ascertained that every milk cow robs the land annually of as much phosphate of lime as is present in eighty-two pounds of bone-dust. From being thus gradually despoiled of this valuable mineral, the Cheshire pastures have become less rich in nutritious herbage; and hence the peculiar benefit derived from boning them, - a practice now so extensively and profitably introduced. But the Cheshire farmers found that after their land had been limed, bones were, to a great degree, a failure ; while, conversely, some observed that, after a heavy boning, lime was not so immediately remunerative. The analysis of the soils and of the limes usually applied in that county, cleared up both appearances. The soil being poor, both in lime and in phosphoric acid, — the two ingredients of bone-earth, - was less grateful for the after application of lime, because the bones had already given it a certain dose of this substance; and, on the other hand, the soil was less remarkably affected by bones, because of the notable quantity of phosphoric acid which lime of a certain quality had previously conveyed to it.

The money value to practical men of an accurate knowledge of calcareous substances, is strikingly illustrated by the fact that a few years ago a patent was obtained for the process of burning the shell-sand (sea-sand mixed with fragments of shells) which occurs so abundantly on the coasts of Cornwall and of the Western Isles. Plausible statements concerning the value of this burned sand as a manure were circulated and believed; and much money was wastefully expended in the purchase of it. The publication of an analysis of its contents by a competent authority at once destroyed the charm; and protected the farmer from further imposition, - at least, in this particular.

Even the theoretical views of men of science in regard to fertilising substances have often a direct bearing upon practice. In England we are fond of novelty; and we frequently yield our assent to scientific opinions when given forth with sufficient confidence, and expend our money in obedience to them. It is far from true that, by despising and neglecting science himself

, the practical farmer escapes from its influence. The speculations of the men he underrates affect in an important degree the profits of his class notwithstanding. Of this we can now give a striking illustration. Analysis in the laboratory of the chemist had ascertained that ammonia exists in the atmosphere to a certain extent, and that plants always contain a quantity of mineral matter, derived from the soil. In the meantime experience had found in the field, that mineral substances, such as saltpetre, nitrate of soda, gypsum, common salt, &c., were often extremely beneficial when applied alone to our growing crops. Upon these facts, Liebig ventured boldly to propound two opinions first, that the application to the soil of substances containing nitrogen was wholly unnecessary, because the ammonia of the atmosphere was sufficient to supply all they required of this ingredient*; and next, that a proper admixture of mineral substances was all that a manure need contain in order to render the land fertile for any crop. Thus mineral manures were strenuously recommended

-alone, and for all soils. Proceeding upon the assumption that the rains are continually washing from the soil its mineral constituents in proportion as they became dissolved, he next concluded that the action of his mineral mixtures would be more permanent and efficient if, by some chemical process, they were rendered more sparingly soluble in water. Hence the origin of the patent manures called after his name. They profess to contain all the substances which the crops for which they are intended can require from the soil, and to contain them in a state in which the rains would not readily remove them.

The love of novelty, assisted by faith in a deservedly high name, has caused thousands of pounds to be spent in the manufacture of these manures, and many more thousands in the purchase of them; while even larger sums have been lost by the more or less partial failure of the crops they were intended to improve. It was in vain that more cautious practitioners warned their brethren by their own experience; which the more complete and correct deductions of science have since confirmed and explained. Manures containing nitrogen are available in all soils in promoting luxuriance of growth: But the solubility of such substances as saltpetre and common salt is one of the very properties on which their immediate and successful action upon plants depends. It required the successive crops of two harvests, however, to convince the parties of their imprudence.

* The reader is, probably, aware that ammonia consists of the two gases, - nitrogen and hydrogen.

These insoluble inanures have now disappeared from the British markets; purely mineral mixtures, however, still retain an uncertain and temporary hold upon public favour. But two facts are sure to banish them from the list of fertilising substances, which can generally be relied upon in all soils and for all crops. These are, first, that plants do really obtain and require from the soil certain forms of organic food; and, secondly, that all naturally fertile soils do contain a sensible proportion of such organic matter. Suppose a soil to be deficient in this organic matter, a purely mineral manure, however compounded, cannot supply it; and the application of such a manure upon such soils must be followed by a failure. But let it be naturally rich in such matter, and the mineral mixture may possibly be applied with a profit.

It must appear, therefore, how economically important it is to practical agriculture, that science should be steadily and cautiously prosecuted in its behalf; and that the best safeguard of the farmer's pocket is a knowledge of the scientific principles on which his art eventually rests. Without that knowledge, however much he may undervalue it, he is at the mercy of every rash hypothesis, and may be induced to expend his money upon the nostrums of mere money-seeking quack-salvers.

Thirdly. The Dairy and the feeding of stock form another general branch of husbandry, to which science has been of no less positive use, than to the two departments which in the preceding pages have principally engaged our attention. Indeed, this must have already struck the reader, from what we have said upon the subject of food, and from the brief allusion we have made to the specially exhausting effects of the dairy husbandry upon the soils of Cheshire, and the mode of repairing them which chemistry supplies.

In the case of dairy farms, the chemical examination of milk drawn from different animals, and under very varying circumstances, has provided us with a body of facts which admit of numerous profitable applications. Thus it is ascertained that the curd and the butter of milk correspond to the muscle and fat of the animal. Hence the reason why good milkers are generally poor in condition, and why the milk falls off when they begin to fatten. And as the curd and butter, like muscle and fat, are derived immediately from the food which the cow eats, and as we know the respective sources of these, we can in some measure control the proportion of each which the milk shall contain. If it is to be rich in butter, we select a food which, like linseed or linseed cake, is naturally rich in oil, or we mix other cheaper forms of fatty matter directly with the ordinary food. If curd (or cheese) is our object, we give food, such as beans and cabbage, which analysis has shown to be rich in gluten, or in some other of the so-called protein compounds. And if, while we are rearing calves, we wish to sell the milk which is high in price, we can, from our knowledge of the composition of milk, and of the various kinds of food at our command, provide an artificial substitute which will serve exactly the same purpose in feeding and rearing the calf, and yet cost less money than the sale of the milk brings in.

Our limits do not permit us to introduce other detailed illustrations of the uses of chemistry to the dairy. Why butter is hard or soft — how its quality is to be improved or maintained - how it is to be best preserved -- why it becomes rancid, and how such a change is to be prevented—what takes place during the process of churning, what during that of natural or artificial curdling-what is the nature of rennet, and how it acts—in what manner we can prepare an artificial substitute for rennet which shall be easily made and constant in its composition, quality, and effect - how cheese should be salted — what kind of salt employed — why difficulties occasionally arise in the storing of cheese—how they are to be overcome or prevented ;— these and many similar questions are treated of in the works before us of the latest date. The mere enumeration of them is all that can be wanted to demonstrate how very extensive, and how practically and economically useful, are the applications of chemical science to the pursuits of the dairy farmer.

In our climate, the rearing and feeding of Stock is scarcely second in importance, as a source of rural profit, to the growing of corn; and there are many who think that under our altered fiscal regulations it must and ought to become the more important of the two. It is certain that, so far as climatic conditions go, green crops appear to be more natural productions of our rainy islands than crops of corn. But, for the feeding of animals science has done at least as much as for the culture and fertilising of the land. The several purposes which are promoted by food have been investigated—what it must be fitted to serve if it is to keep an animal in a healthy condition - what is the composition of each of the more common kinds of food on which animals are nourished - how, what is given to the animal must be adapted to its period of growth, to the purposes for which it is fed (for work, for beef or mutton, for milk, for growth, &c.), and to the conditions of temperature, &c. in which it is placed — why one kind of food will keep an animal in condition for hard or fast work, while another makes him heavy, sleek, or fatwhy the same kind of root crops are not always equally nutritive,

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