Horticultural Chemistry.

Mr. B. At no former period has the science of Chemistry been brought to greater perfection, nor has it been applied to so many useful purposes of life as it is at the present time. Its terms have even been introduced into common conversation; for, in every description of things in common usewhether fluid or solid-we are sure to hear somewhat of alcohol, nitrogen, oxygen, carbon, or ammonia. Druggists, brewers, distillers, compounders, dyers, &c., must all be more or less acquainted with chemistry, and to all of those the science is more or less useful. But it is not intended to be solely confined to these trades and professions, the friends of both farmers and gardeners are urgent in their recommendations of the same to both these classes, promising them that a competent knowledge of it would greatly assist them in the choice, preparation and application of manure. I therefore feel a pleasure in having an opportunity of lending my feeble aid to communicate to you even the rudiments of such an interesting and useful science—a science by the aid of which we can solve the most difficult problems which Nature presents; we can understand the elementary particles of every compound body of which this earth is composed and the atmosphere around it, and understand the reason of its adaptation to the support of animal and vegetable life. It teaches us the confirmed proportion with which simple bodies unite with each other, and it gives us the means (in horticulture) of ascertaining the cause of these phenomena, which, though of constant occurrence, are yet inexplicable to the mere practical man.

Son. Mr. Voelcker tells us that a general knowledge of the principles of farming, however useful to the practical farmer, never will help him to grow a large crop of turnips; he must have special training in practical matters in order to be a successful farmer.

Mr. B. We are also told, by the same authority, that so it is with chemical knowledge. Men may have excellent general chemical knowledge, but if they have not special chemical knowledge in relation to farming, their labours will be of little direct utility to the agriculturalist. Men of science may make known, as far as they are able, the laws of nature, they may place in the most evident light the strong necessity of being guided by true knowledge rather than by chance, but they can do no more, it rests with the actual cultivator to prove how great are the benefits to be derived from a rational course of proceeding.

It does not require the aid of science to tell us that plants require food, nor is it necessary to be profound to know that all food is not alike nourishing. But science has shown us that all plants require certain sorts of nourishment, and that without these they will not flourish. Almost every plant has a different composition in some respect, and a variety of food or manure is therefore necessary.

The manner in which we are to proceed in these inquiries. -the knowledge of the matters contained in plants-the various sources from whence a supply of nourishment can advantageously be obtained-the preparation and preservation of manures, are taught by chemistry. The great bulk of the atmosphere is composed of two gases in the state of simple mixture, they are called oxygen and nitrogen, the latter of which exists in much larger quantity in the air than the former, while in the substances which form the crust of the earth, generally oxygen constitutes the one half.

Son. We are told that the quantity of oxygen in the materials of our earth is also very great, almost all the soils, rocks, and minerals being compounds of oxygen. The atmosphere contains 21 per cent. of its volume, and every 90 lbs. of water contains 80 of oxygen.

Mr. B. Oxygen is an invisible and almost intangible substance, yet endowed with such important qualities that it is the great cause of almost all the phenomena of animal and vegetable life. In animals it is the cause of heat. In plants germination is owing to its influence-it is the supporter of combustion, and fire would be extinguished without it; while all the changes in the elements of our earth are more or less owing to its action.

Although most persons think of it only as an air or gas, possibly there is not a millionth part of the quantity of oxygen in the world existing as air. It assumes a singular variety of character in its different combinations. Thus, with hydrogen it forms water; with lead it forms the substance called red lead; with nitrogen in one proportion, it forms atmospheric air, in another proportion the nitrous oxide, or what is called the laughing gas; in a third the acid called aquafortis, with sulphur it forms the sulphuric acid or oil of vitriol, with iron and its metals it forms their ores, called oxides, and so forth. The other element of the atmosphere is called nitrogen, and in the condition in which it is there presented, serves merely as a means of diluting the oxygen with which it is mixed. It forms about three-fourths of the atmosphere, one fourth of animal flesh, and is found in small quantities in other combinations. "remains a gas at

Son. "Atmospheric air" Mudie says,

all the natural temperatures of the surface of our globe; and, therefore, it is of all substances the most serviceable, especially in the economy of the vegetable and animal kingdoms, as no member of either of these kingdoms can be developed, brought to maturity, or even exist without its presence. Reaching from above the summits of the highest mountains, and penetrating downwards into the depths of the ocean, probably beneath the lowest glimmer of the solar light, it appears to be the stimulating principle of the whole of organic nature, and one which is everywhere present."

Mr. B. The basis of the atmosphere has been proved to be of the same chemical composition in all the regions of the globe. All the varieties of climate will therefore be found to depend on the modifications impressed upon it by light, heat, and moisture, and over these art has obtained even in the open air a greater influence than at first sight would appear to be possible. By judicious management the climate of our gardens is rendered congenial to the luxurious productions of more favoured regions, and flowers and fruits from the confines of the tropics flourishing in the open air, daily prove the triumphs of knowledge and industry.

Although oxygen and nitrogen are the two chief constituents of the atmosphere of our earth there exists in the air, in sufficient quantities to produce great effects, other bodies which are the result of the respiration of animals, and the decay or putrefaction of organic substances. These substances do not form any very considerable part of the air; and though this is the case their proportion in general is very constant, that is to say, the actual quantity in the great bulk of the atmosphere is the same, the distribution is sometimes unequal. They are continually being evolved into the air, but they do not increase in quantity; they are used by plants and again become part of the organised world.

The continued respiration of animals, the combustion of fuel, and the decay of various matters send into the atmosphere and supply to the soil, immense quantities of carbonic acid, a compound of carbon and oxygen, which is the means of supplying plants with almost all the carbon which they contain. The carbonic acid sent forth by animal and other causes is decomposed by plants, its carbon being received into and made part of their tissues, and its oxygen being again returned to the air to combine again with fresh portions of carbon and again to be evolved. A property enjoyed by carbonic acid gas is, that it dissolves the hard ingredients of the soil, water charged with the gas will dissolve chalk, even bones, upon which distilled water has scarce any influence. Plants obtain supplies of carbonic acid from the atmosphere

in two ways: 1st, by direct absorption through the leaves, this occurs in all plants, and in a very remarkable degree in those whose roots bear but small proportion to their stems and leaves. 2nd.-They obtain carbonic acid dissolved in water by absorption through the roots. Herbaceous plants, such as form the staple of garden culture, seem in their young state to be greatly dependent on a supply of carbonic acid from the soil, and to thrive well only in soils where there is a large supply of carbonic acid from decay; but when the leaves and green plants are fully developed they draw largely on the carbonic acid of the air. In nature carbonic acid is produced under a great variety of circumstances. It is given off from the lungs of all animals during respiration, and from the leaves and green parts of plants during the absence of the sun. It is formed during the progress of fermentation. During the decay of animal and vegetable substances in the air, in compost heaps, or in the soil, it is evolved in great abundance. In certain volcanic countries it issues in large quantities from springs, and from cracks and fissures in the surface of the earth, while the vast amount of carbon contained in the wood and coal daily consumed by burning is carried up into the atmosphere chiefly in the form of carbonic acid. The other body which exists with carbonic acid in the atmosphere is ammonia, which is the same substance as hartshorn and its carbonate is the common smelling salts of the shops. It is composed of carbon and nitrogen, and is a volatile compound produced in great quantities during the decomposition and putrefaction of all organic bodies which contain the elements of which it is composed. The bodies of animals—their dung and decaying vegetable matter, are, in the processes of putre faction, sources of this substance.

Ammonia exists in the atmosphere, and every shower which falls to the earth carries this body with it, and spreads it uniformly over the soil. While, on the other hand, the continued decay of dead matter sends ever fresh supplies to be carried again to the soil. Ammonia contains 82 per cent. of the most important element, nitrogen, and not only exists in the air, but constitutes the most active part in all manures produced by the decay of animal and vegetable bodies.

Geology.

Mr. B. Having in my first lesson given you some kind of insight into the practical utility of geology, I will now endeavour to give you the rudiments at least of the science, and as

much of the details as I think will be sufficient for your information, and for laying the foundation of a more profound knowledge of the subject if you are disposed for more extensive acquirements.

In tracing the nature and mode of operation of all kinds of physical agents that have at any time and in any manner affected the surface and interior of the earth, we find fire and water in the foremost rank of these agents, those are two universal and antagonizing forces which have most materially influenced the condition of the globe; and which man has also converted into the most efficient instruments of his power and obedient auxiliaries of his mechanical and chemical and culinary operations.

It is computed that our globe is in diameter, that is, from its upper surface to its lower one, about 8000 miles, and the crust of the earth to be 400 miles in thickness. It is therefore reasonable to imagine, that in a crust of 400 miles thick it would be very probable for deep and immense lakes, or large seas of melted matter to exist and be widely distributed in subterranean caverns. Various observations and various experiments with the pendulum have proved that our planet is not an empty sphere, but that its interior, whether fluid or solid, has a higher specific gravity than the materials of the crust. From the same experiments it has been inferred that there is a gradual and regular increase in its density from the surface to the centre.

The action of the volcanoes, and the rise of hot springs to the surface, prove that there are subterranean sources of heat active somewhere. It is well known that the temperature of the crust of the earth increases the deeper you descend into it. In the Northumberland coal pit the heat of the rocks increases by one degree of Farenheit's thermometer for every 44 feet in descent. A French geologist, M. Cordier, has paid much attention to this subject. His conclusions are,-1st. That the heat increases rapidly the deeper you go. 2. That the increase is not equal at equal depths, but varies in different countries. 3. That the average increase over the whole earth is one degree for every 45 feet in descent. In the Cornish mines there are considerable streams of water of the temperature of from 80 to 90 degrees, which is from 30 to 40 degrees warmer than the water on the surface. Some have conjectured that this increase of heat in the descent of mines is owing to the condensation of air, but it is not so. A Cornish geologist, Mr. Fox, has shown that the mines are ventilated by numerous shafts from the surface of the earth, descending in some shafts and ascending in others. In all the upper currents are warmer than the descending ones.

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