place it for half an hour in a warm place; if there is any adulteration of lime, a remarkably brisk effervescence will ensue, and the lime will be dissolved. Let the whole be then poured upon a piece of fine linen stretched over another vessel, and rinse the vessel and the linen strainer a few times with water. Upon this, place the strainer with the residue left thereon in some warm situation, to dry, and when completely dried, rub off and weigh the dry mass. The loss of weight will declare how much lime and water were present in the bone-dust. A good and dry specimen will lose by

this treatment one drachm at the most.

Should the powder, after the vinegar has been poured off, begin again to effervesce when fresh vinegar is added, it must then be made warm and treated for the second time with a fresh quantity of vinegar. Any admixture of earth, sand, &c., will be easily perceived by the eye in the residue, after a previous washing if requisite. In order to be assured of the presence of lime in the decanted vinegar, it is simply necessary to add some sulphuric acid to it, whereby gypsum or sulphate of lime is formed, which, from its great difficulty of solution, falls as a white sediment to the bottom.

3. Test by combustion.—If half an ounce of bone-dust is suffered to stand in an iron spoon over red-hot coals until all the gelatine is burned away, and the residue has again become white, the quantity of the latter is learned by the loss of weight. Good and dry bone-dust loses by this treatment full one-fourth of its weight; that is, from half an ounce, a full drachm. When lime or other earthy substances are intermixed, less of course will disappear. This test is, however, by no means so well adapted for powdered bones as for guano (pp. 134, 135), because it is requisite to continue the action of heat for several hours in order to consume the whole of the gelatine; and from this circumstance the differences that are developed between good and bad specimens are much smaller, and consequently less palpable and clear, than in the various sorts of guano.

X. OIL-CAKE AND MALT-DUST.

ENGLAND imports at the present day nearly 1,500,000 cwt. of oil-cake for the purposes of feeding her cattle and fertilizing her fields. Of this amount Germany contributes fully one-fourth, and France at least half. In this way alone 400,000 cwt. of provender and manure are annually lost to German agriculture, which, if used exclusively as a means of manure, might yield, at the lowest estimate, 600,000 Saxon bushels of rye, besides a corresponding quantity of straw. Were this oil-cake employed, again, simply as fodder, at least 80,000 cwt. of meat, in addition to some 450,000 bushels of rye, &c., obtained from the surplusage by its conversion to manure, might also be produced. If this produce is valued at an extremely low price (1 Saxon bushel of rye at 6s., the straw at one-fourth of the pecuniary value of the grain, and 1 lb. of meat at 3d.), it, follows that the oil-cake exported from Germany would realize on the first supposition £225,000, or 1,500,000 dollars, and on the second, £300,000, or 2,000,000 dollars. But now Germany receives in compensation only some £45,000, or 300,000 dollars, and therefore voluntarily renounces a gain from five to six times greater, which it might derive from these substances.

These figures, which have been drawn not merely from theoretical speculations, but from the practical testimony and experience of agriculture itself, ought to be to every German farmer a voice of warning, calling to him thus: "Keep what thou hast; and manure with thy wares, not foreign fields, but thine own." In Saxony this is done already, and the two years just elapsed have especially extended the practice of manuring with rape-meal, partly in consequence of abundant instruction respecting the constituents and strength of this manure, and partly in consequence of the recurrence of a deficient supply of guano and bone-dust, which necessitated the employment of substitutes for them." The use of oil-cake as provender has also increased in a similar manner. Precise statistics with respect to the magnitude of the yearly consumption cannot indeed at present be brought forward; but no great error will be committed

in assuming that Saxon agriculture itself now consumes again the residuum of the oleaginous seeds, whose cultivation in Saxony, and even in its mountainous regions, has received during the last ten years a very extraordinary extension, and that, in all probability, it will before long import from neighbouring countries. In several districts, a custom that deserves the highest commendation has been introduced very generally into trade, by which the farmer sends his seed to the oil-mill upon condition that the cake produced from it is returned to himself.

1. COMPOSITION AND EFFECTS OF OIL-CAKE.

The following figures may, in the first place, show in what way the seeds of oil plants differ in point of chemical composition from their vegetative parts or straw:

According to this analysis, rape-straw is richer in valuable manuring substances than the straw of the various kinds of grain, whose composition has been stated in page 102. Besides the constituents just enumerated, it often contains considerable quantities of common salt and gypsum, which of course enhance its worth as a manure. As, however, from its woody nature, it is in its natural state difficult to incorporate with the soil, and is but very slowly decomposed there, it is advantageous to let it lie until it becomes sufficiently rotten, upon the dung-hill, or in firmly troddendown heaps, which should be from time to time moistened with water or drainings, to which some sulphuric acid has been added.

Rape-seed possesses, in common with other seeds, great

M

abundance of nitrogen and phosphoric acid, but, on the other hand, differs from those of the various kinds of grain, leguminous crops, &c., in the circumstance of its containing, instead of starch, another substance devoid of nitrogen, namely fixed oil. In the use made of this seed in oil-mills, it loses chiefly oil, together with a small quantity of mucilage and albumen; all its remaining constituents are left behind. As the oil possesses no manuring efficacy, the cakes remaining after its removal must necessarily contain, proportionately, more manuring elements than the seed from which they were prepared, as is testified by the following analyses of several sorts of oil-cake that are made use of in Saxony as manure for land.

100 lbs. (perfectly dried) contained :

The preceding figures relate to perfectly dry oil-cake, not such as is met with in commerce. The cake as furnished by the oil-mills invariably contains water, and on an average ealculation about 12 per cent.; consequently, the value above stated must be reduced about one-eighth, and reckoned at from 3s. to 3s. 6d. per cwt. It will be seen that the difference in the sorts which may be regarded as most extensively used in Germany is of no great importance, and hence their manuring value may be considered very nearly equal. As the price of rocket-cake, which does not furnish an agreeable food for stock, is usually lower than that of rape and colza-cake, it is especially recommended as a very cheap manure. According to the prices current in England, a hundredweight of rape-cake is there bought at 68. 6d., and is, therefore, more than twice as expensive as in

Germany, where it can now be obtained for from 2s. to 3s. If English agriculturists find it worth their while, as must be the case, to purchase oil-cake at this high price, it may surely be expected that the German farmer, who can procure it at less than half the expense, will find it profitable.

a. Oil-cake as a Manure.

On looking at the constituents of oil-cake, no doubt can be entertained which of its ingredients plays the principal part in its operation as a manure. It is certainly the nitrogen, or, to speak more accurately, the nitrogenous substances. (albumen, &c.), of which it contains nearly as much as bone-dust, and about one-third as much as good guano. To develope the forcing action dependent on this, a previous putrefaction and conversion of the nitrogenous into ammoniacal combinations is here again necessary; but this ensues more rapidly in oil-cake than in bones, because it is more easily penetrated by water and air, and hence it is not essential to induce putrefactive decomposition before ploughing it into the ground. Experience agrees entirely with the statement, that it acts more speedily than bone-dust, but, on the other hand, more slowly than guano; as also, that its principal effect takes place during the first year, except, perhaps, in a very dry season, in which it does not find in the earth the amount of moisture required for its decomposition.

Next to nitrogen, the action of oil-cake (in forming seed) is due to the phosphoric acid in it, of which, however, it contains about five times less than good guano, ten times less than bone-dust, and twelve to fourteen times less than bad guano. That, moreover, the other ingredients met withpotash, soda, lime, as also the organic, humus-forming substances, and, in addition to these, the common salt and gypsum that may perhaps be present-increase the efficacious operation of oil-cake, cannot be denied; nevertheless, the same importance cannot be attributed to these ingredients as to the first, because they are contained in oil-cake in no greater quantity than in barley-straw, oat-straw, &c.

Respecting the total power of oil-cake as a manure, and its duration, I am not yet able to adduce such precise figures as those placed at my disposal, by the practical experience of