it. That its principal operation takes place during the first year, and that its persistent effects are very inconsiderable, it is now scarcely necessary to mention, and just as little the testimony of experience, that a strong manuring with it may easily induce the lodgement of the corn. The manuring value of malt-dust, as met with in commerce, must be regarded as about equal to that of oil-cake. In Saxony it is now purchased at from 1s. 7d. to 2s. 5d. per cwt., and is more particularly used as a dressing for meadows and garden-grass, or as an addition to stable-muck; more rarely as an independent manure, in which case from 10 to 12 cwt. are allowed to the (Saxon) acre (about equal to 14 English acre). When employed as fodder, the strength of stable-manure is increased by its means in no insignificant degree.

THE more high cultivation spreads, the greater becomes the consumption of nitrogen and phosphoric acid, on the one hand, to furnish abundant and powerful food to stock; on the other, to afford the crops abundant and powerful manure. Agricultural chemistry must employ part of its activity in hunting through the treasury of nature, to see whether there are not in existence, natural bodies in which these two substances lie hidden. It has further to provide that ways and means shall be pointed out for converting these substances into a free, assimilable and digestible form, when they are too firmly combined for the plants themselves to dissolve and absorb them; or, in case they are too bulky, and hence unsuitable for distant transport, to compress them into a smaller space, so that, for instance, 1 cwt. of

substance may be as rich in manuring matter as 10, 20 or 30 cwt. of the raw material.

Chemistry has already displayed its activity in all these directions. Vast deposits of a salt (nitrate of soda) very rich in nitrogen have been discovered in the strata of Chili and Peru; enormous deposits of fossilized bones ("coprolites"), rich in phosphate of lime, have been found in certain rocks of England and North America, and have at once been brought into use*. The nitrogen which is contained in coal, but so firmly combined that not even a lengthened exposure to the decomposing influence of the soil renders it soluble, is condensed rapidly and converted into nourishing ammonia, when the coal is heated in closed vessels, as, for example, in the manufacture of gas. Hundreds of tons of ammoniacal salts are now obtained from the formerly waste wash-water of coal-gas, giving, when mixed with dissolved coprolites, a manure containing the same constituents as the best guano, and acting with equal vigour upon vegetation, as is evidenced by the great consumption of it in English agriculture. In like manner the important problem, how to appropriate to agriculture the enormous masses of manuring matters contained in the cesspools and sewers of large towns, and now in great part lost,— by mechanically and chemically transforming them so as to render them portable and active, approaches every day nearer to its solution, especially in France, where the night-soil of dwellings, and the refuse of the slaughterhouses, &c., are already converted in large quantities into manures, so concentrated, that they are even exported to the West Indian colonies, to apply to the sugar and cotton plantations.

And in the face of such facts we still frequently hear the question: What is the use of chemistry to agriculture? what has chemistry done for it? Now I should think, that if, as stated, chemistry has helped to provide the animal and vegetable worlds of the present day with food from fossil bones and coal, that is, from the remnants of an extinct animal and vegetable creation, that alone would be use enough, even if chemistry had not accomplished and could not accomplish more. Far higher however is the intellecSee note, page 143.

tual gain to be prized, even if not capable of being immediately turned into money, which chemical knowledge insures to the agriculturist, in giving him an insight into the quiet laboratory of nature,-to the operations of which he must adapt his proceedings,-and thereby placing his calling on the basis of practical reasoning.

Most of the manures comprised here are remarkable for a great abundance of assimilable nitrogen (ammonia or nitric acid), and hence exert pre-eminently a vigorously stimulating power upon the growth of plants, like Peruvian guano, from which however they are distinguished by the absence or at least less abundant proportion of phosphoric acid. Although this deficiency of seed-producing matters may make them seem less suitable for manuring, they must be regarded as excellent materials for 'dressings and stimulants, when used jointly with the more slowly-acting manures, such as stable-dung, bone-dust, &c., since they supply to these that which they want: readily assimilable nitrogen, or 'forcing power. The circumstances which as yet oppose their general diffusion is their high price, so that they cannot be brought into actual competition with guano. But this price is by no means a necessary one, as it would be, for instance, if no great supply of them existed in nature or could be produced by art; it is only still so high because the demand has not yet been sufficiently great to call for their manufacture and introduction into commerce on a large scale. With increasing demand and consumption, not only will the means of supply become enlarged and extended, but the cost of production and transport will be correspondingly diminished and lowered*.

SALTS OF AMMONIA.

There can be no doubt that ammonia, which may be imagined as putrefied nitrogen, is that constituent of manures which in by far the majority of cases gives the stimulating property. Pure and free ammonia is a gas of alkaline nature and pungent odour; when combined with acids, losing its volatility, it becomes fixed; losing likewise its alkaline nature, it becomes neutral; losing its pungent odour, it be

* While an increased stimulus is now given by the growing difficulty of obtaining guano.

comes scentless. An exception to this is offered by carbonic acid, which forms with ammonia a compound which retains the ammoniacal odour and the volatility. These compounds of ammonia with acids have the appearance and properties of salts; they are called ammoniacal salts. Those best known are-chloride of ammonia (muriate of ammonia) or sal-ammoniac, sulphate of ammonia, nitrate of ammonia, humate of ammonia, and carbonate of ammonia (salt of hartshorn).

All these ammoniacal salts act with equal rapidity and vigour as manures and stimuli of vegetable growth, as has been demonstrated beyond all question by innumerable experiments. And these same salts constitute the forcing power, not only in guano, but also in stable-manure and decomposed urine, since the nitrogen of these last two manures takes the form of ammonia in the process of decomposition.

If decay were the only process by which the nitrogen of animal and vegetable substances could be transformed into ammonia, it would be out of the question to use ammoniacal salts for manuring, since it would always be more profitable to employ these materials in substance, than the ammonia or ammoniacal salts extracted from them. But, as already indicated, there is a second way to this conversion, which consists in heating the organic bodies containing nitrogen, with exclusion of the air; their nitrogen is then also changed into ammonia, which is volatilized, with the other vapours or gases produced by the heating, and separated on cooling as carbonate of ammonia, from which any other ammoniacal salt may be formed, by adding sulphuric, hydrochloric or other acid, which drives out the carbonic acid and combines with the ammonia in its place. This is the ordinary mode in which sal-ammoniac and other salts of ammonia are obtained in chemical manufactures.

In this manner it is possible to extract powerfully manuring constituents even from substances which do not decay in the earth, and hence cannot act as manures, for example, from coal. All coal contains nitrogen, but this is so firmly combined with the mass of carbon, that even if the coal were applied in powder the plants would not be helped, as we said before; in this condition it is and remains undecomposable and insoluble. Heat loosens this combination and causes the

conversion of the nitrogen into ammonia, when the atmospheric air is excluded. These conditions are fulfilled especially in the manufacture of gas for illumination, in which the coal is heated in closed iron cylinders. The gas-liquor obtained in the cooling and purification of the gas, contains in solution so much ammonia, that it pays very well to convert this into sulphate of ammonia by adding sulphuric acid, or into sal-ammoniac by adding hydrochloric acid, and to bring the salt thus formed (no longer volatilized with the watery vapours) into a dry condition by driving off the water. In this way several hundred pounds worth of sulphate of ammonia are obtained annually from the gas-liquor of the Dresden Gas-works, which was formerly thrown away. This gives us a standard for reckoning what extraordinary quantities of this salt may be manufactured in England, where almost every town already has its gas-works*.

If we burn coal completely, that is, in a sufficient draught of air, no ammonia is produced from the nitrogen, which takes the form of a gas, and is diffused, with the smoke, into the atmosphere, as uncombined nitrogen. In our stoves and other heating apparatus, there is never a perfect combustion of the coal, otherwise there would be no smell and no soot; so that here also there is always some ammonia produced, which is partly condensed with the soot. It is well known that slacked lime will set free and drive out the ammonia combined in ammoniacal salts. If we rub up a little coalsoot with slacked lime, the sharp, pungent odour developed, denotes clearly enough that a large quantity of combined ammonia is contained in it. This is the principal reason why

* The value of the ammoniacal liquor of gas-works is fully appreciated in England and used very extensively in the manufacture of ammoniacal salts, and also in a diluted condition as a liquid application to land. The quantity of ammonia in the liquid varies; some will give, with muriatic acid, as much as 1 lb. of sal-ammoniac to the gallon. The gas-liquor of the London works is said to yield 14 oz. of sulphate of ammonia per gallon, when saturated with sulphuric acid.

Diluted ammoniacal liquor is often applied by means of the wateringcart to grass land, like liquid drainings; it is likewise used with advantage to moisten compost heaps and hasten the fermentation of peat, and slowly decomposing vegetable matters. In combination with bone-dust, it forms a most valuable manure.-A. H.