Sir Humphry Davy was a scientist, an inventor, a poet, and a personality. The combination of his personality and his talent for science made him a brilliant lecturer, so much so that he became famous for them, with his lectures becoming a social event. From 1803, he delivered a series of well-prepared lectures to the board of agriculture; the content and the spirit of these lectures are captured in Elements of Agricultural Chemistry. These lectures became the inspiration for the development of agricultural ...
Sir Humphry Davy was a scientist, an inventor, a poet, and a personality. The combination of his personality and his talent for science made him a brilliant lecturer, so much so that he became famous for them, with his lectures becoming a social event. From 1803, he delivered a series of well-prepared lectures to the board of agriculture; the content and the spirit of these lectures are captured in Elements of Agricultural Chemistry. These lectures became the inspiration for the development of agricultural chemistry and were a major stepping-stone in the development of soil science and fertilizers.
INTRODUCTION. - GENERAL VIEWS OF THE OBJECTS OF THE COURSE, AND OF THE ORDER IN WHICH THEY ARE TO BE DISCUSSED.
IT is with great pleasure that I receive the permission to address so distinguished and enlightened an Audience on the subject of Agricultural Chemistry. That any thing which I am able to bring forward, should be thought worthy the attention of the Board of Agriculture, I consider as an honour; and I shall endeavour to prove my gratitude, by employing every exertion to illustrate this department of knowledge, and to point out its uses.
In attempting these objects, the peculiar state of the enquiry presents many difficulties to a Lecturer. Agricultural Chemistry has not yet received a regular and systematic form. It has been pursued by competent experimenters for a short time only; the doctrines have not as yet been collected into any elementary treatise; and on an occasion when I am obliged to trust so much to my own arrangements, and to my own limited information, I cannot but feel diffident as to the interest that may be excited, and doubtful of the success of the undertaking. I know, however, that your candour will induce you not to expect any thing like a finished work upon a science as yet in its infancy; and I am sure you will receive with indulgence the first attempt made to illustrate it, in a distinct course of public lectures.
Agricultural Chemistry has for its objects all those changes in the arrangements of matter connected with the growth and nourish ment of plants; the comparative values of their produce as food; the constitution of soils; the manner in which lands are enriched by manure, or rendered fertile by the different processes of cultivation. Enquiries of such a nature cannot but be interesting and important, both to the theoretical agriculturist, and to the practical farmer. To the first, they are necessary in supplying most of the fundamental principles on which the theory of the art depends. To the second, they are useful in affording simple and easy experiments for directing his labours, and for enabling him to pursue a certain and systematic plan of improvement.
It is scarcely possible to enter upon any investigation in agriculture without finding it connected, more or less, with doctrines or elucidations derived from chemistry. If land be unproductive, and a system of ameliorating it is to be attempted, the sure method of obtaining the object is by determining the cause of its sterility, which must necessarily depend upon some defect in the constitution of the soil, which may be easily discovered by chemical analysis.
Some lands of good apparent texture are yet sterile in a high degree; and common observation and common practice afford no means of ascertaining the cause, or of removing the effect. The application of chemical tests in such cases is obvious; for the soil must contain some noxious principle which may be easily discovered, and probably easily destroyed.
Are any of the salts of iron present? they may be decomposed by lime. Is there an excess of siliceous sand? the system of improvement must depend on the application of clay and calcareous matter. Is there a defect of calcareous matter? the remedy is obvious. Is an excess of vegetable matter indicated? it may be removed by liming, paring, and burning. Is there a deficiency of vegetable matter? it is to be supplied by manure.
A question concerning the different kinds of limestone to be employed in cultivation often occurs. To determine this fully in the common way of experience, would demand a considerable time, perhaps some years, and trials which might be injurious to crops; but by simple chemical tests the nature of a limestone is discovered in a few minutes; and the fitness of its application, whether as a manure for different soils, or as a cement, determined.
Peat earth of a certain consistence and composition is an excellent manure; but there are some varieties of peats which contain so large a quantity of ferruginous matter as to be absolutely poisonous to plants. Nothing can be more simple than the chemical operation for determining the nature, and the probable uses of a substance of this kind. There has been no question on which more difference of opinion has existed, than that of the state in which manure ought to be ploughed into the land; whether recent, or when it has gone through the process of fermentation? and this question is still a subject of discussion; but whoever will refer to the simplest principles of chemistry, cannot entertain a doubt on the subject. As soon as dung begins to decompose, it throws off its volatile parts, which are the most valuable and most efficient. Dung which has fermented, so as to become a mere soft cohesive mass, has generally lost from one third to one half of its most useful constituent elements. It evidently should be applied as soon as fermentation begins, that it may exert its full action upon the plant, and lose none of its nutritive powers.
It would be easy to adduce a multitude of other instances of the same kind; but sufficient I trust has been said to prove, that the connexion of Chemistry with Agriculture is not founded on mere vague speculation, but that it offers principles which ought to be understood and followed, and which in their progression and ultimate results, can hardly fail to be highly beneficial to the community.