1838] 



FARMERS' REGISTER 



681 



pend upon the powers of plants to absorb or de- 

 compose the puirelyinj^ or decayin<T remains of 

 animals ami vecretahlcp, anil (he <raseouR ellluvia 

 wliich they are cnnstaiiily einiliing. Carbonic 

 acid gas is Ibrnied in a variety of processes of fer- 

 mentation and cnmbnstion, and in the respiration 

 of animals; and, as yet, no other process is known 

 in nature by which it can be consumed, except 

 vegetation. Animals produce a substance which 

 appears to be a necessary food of vegetables; 

 vegetables evolve a |)rinciple necessary to the ex- 

 istence of animals; and these different classes of 

 beings seem to he thus connected together in the 

 exercise of their living (unctions, and to a certain 

 extent made to depend upon each other for their 

 existence. Water is raised from the ocean, dif- 

 fused through the air, and poured down upon the 

 soil, so as to be applied to the purposes of life. 

 The diflerent parts of the atmosphere are mingled 

 together by winds or changes of temperature, and 

 successively brought in contact with the surface 

 of the earth, so as to exert their fertilizing influ- 

 ence. The modifications of the soil, and the ap- 

 plication of manures, are placed within the power 

 of man, as if for the purpose of awakening his 

 industry, and of calling forth his powers. 



The theory of the general operation of the more 

 compound manures, may be rendered very ob- 

 vious by simple chemical principles; but there is 

 still much to be discovered, with regard to the best 

 methods of rendering animal and vegetable sub- 

 stances soluble; with respect to the processes of 

 decomposition, how they may be accelerated or 

 retarded, and the means of producing the greatest 

 effects from the materials employed: these sub- 

 jects will be attended to in the lecture on manures. 



Plants are found by analysis to consist princi- 

 pally of charcoal and aeriform matter. They 

 give out by distillation volatile compounds, the 

 elements of which are pure air, inflammable air, 

 coally matter, and azote, or that elastic substance 

 which forms a great part of ttie atmosphere, and 

 which is incapable of supporting combustion. 

 These elements they gain, either by their leaves 

 from the air. or by their roots from the soil. All 

 manures from organized substances contain the 

 principles of vegetable matter, which, during pu- 

 trefaction, are rendered either soluble in water or 

 aeriform — and in these states, they are capable of 

 being assimilated to the vegetable organs. No 

 one principle affords the pabulum of vegetable 

 life; it is neither charcoal nor hydrogen, nor azote, 

 nor oxygen alone; but all of them together, in va- 

 rious stales and various combinations. Organic 

 substances, as soon as they are deprived of vitali- 

 ty, begin to pass through a series of changes, 

 which ends in their complete destruction, in the 

 entire separation and dissipation of the parts. 

 Animal matters are the soonest destroyed by the 

 operation of air, heat, and light. Vegetable sub- 

 stances yield more slowly, but finally obey the 

 same laws.* The i)eriods of the application of 



* This statement in the text, though correct gene- 

 rally, is not without exception. Some vegetable sub- 

 stances undergo change very rapidly; some animal 

 substances very slowly. The expressed juices of most 

 fruits enter into the vinous fermentation as rapidly, or 

 even more rapidly, at the temperature of 70° Fahr. 

 than the animal fluids do the putrefactive; the white 

 tissues of animals, as tendons, &c. resist change with 

 great pertinacity. — J. D. 



manures from decomposing animal and vegetable 

 substances depend upon the knowledge of these 

 |)riiici|)lcs; and I shall be able to ])roduce some 

 new and important facts li)unded upon them, 

 which I trust will remove all doubt from this part 

 of agricultural theory. 



The chemistry ofthe more simple manures, the 

 manures which act in very small <piantities, such 

 as gypsum, alkalies, and various t-:aline substances, 

 has hitherto been exceedingly obscure. It has 

 been generally supposed that the.^e materials iict 

 in the vegetable economy in the same manner as 

 condiments or stimulants in the animal economy, 

 and that they render the common (bod more nu- 

 tritive. It seems, however, a much more proba- 

 ble idea, that they are actually a part of the true 

 food of plants, and that they supply that kind of 

 matter to the vegetable fibre, which is analogous 

 to the bony matter in animal structures. 



The operation of gypsum, it is well known, is 

 extremely capricious in this country, and no cer- 

 tain data have hitherto been offered for its appli- 

 cation. There is, however, good ground for sup- 

 posing that the subject will be fully elucidated by 

 chemical inquiry. Those plants which seem most 

 benefited by its application are plants which al- 

 ways afford it on analysis. Clover, and most of 

 the artificial grasses, contain it; but it exists in very 

 minute quantity only in barley, wheat, and tur- 

 nips. Many peat ashes, which are sold at a con- 

 siderable price, consist in great part of crypsum, 

 with a little iron; and the first seems to jje their 

 most active ingredient. I have examined several 

 of the soils to which these ashes are successfully 

 applied^ and I have (bund in them no sensible 

 quantity of gypsum. In general, cultivated soils 

 contain sufficient of this substance for the use of 

 the grasses; in such cases, its application cannot 

 be advantageous. For plants require only a cer- 

 tain quantity of manure; an excess may be detri- 

 mental, and cannot be useful. 



The theory of the operation of alkaline sub- 

 stances is one of the parts of the chemistry of 

 agriculture most simple and distinct. Tliey'are 

 found in all plants, and therefore may be regarded 

 as amongst their essential ingredients. From their 

 powers of combination, hkewise, they may be 

 usefiil in introducing various principles into the 

 sap of vegetables, which may be subservient to 

 their nourishment. 



The fixed alkalies, which were formerly re- 

 garded as elementary bodies, it has been my good 

 fortune to decompose. They consist of pure air, 

 united to highly inflammable metallic substances; 

 but there is no reason to suppose that they are 

 reduced into their elements in any of the processes 

 of vegetation. 



In this part of the course I shall dwell at consi- 

 derable length on the important subject of lime, 

 and I shall be able to offer some novel views. 



Slacked lime vvas used by the Romans for ma- 

 nuring the soil in which fruit-trees grew. This 

 we are informed by Pliny. Marl had been em- 

 ployed by the Britons and the Gauls from the 

 earliest times, as a top-dressing for land. But the 

 precise period in which burnt lime first came into 

 general use in the cultivation of land, is, I believe, 

 unknown. The orisrin ofthe application from the 

 early practices is sufficiently obvious ; a substance, 

 which had been used with success in garden- 

 ing, must have been soon tried in farming; and in 



