Action of Manures.
The department of agricultural chemistry which has been most largely developed of late years is that connected with the problems of manuring. It is, from a practical point of view, of most value. It is some considerable time since we have recognised that the only three ingredients it is, as a rule, expedient to apply as artificial manures, are nitrogen, phosphoric acid, and potash. The nature, mode of action of the different compounds, and properties of these three substances, and their comparative influence in fostering plant-growth, together with the economic question of which form is, under various circumstances, the most economical for the farmer to use, have together given rise to a large number of "field" and "pot" experiments. As the principles underlying this practice form the subject of the following treatise, any further discussion of the question must be left to the following chapters.
Note.—The reader interested in the historical development of agricultural chemistry is referred to Sir J. H. Gilbert's Presidential Address to the Chemical Section of the British Association, 1880.
FOOTNOTES:
[1] The History of the Chemical Elements. By Sir Henry E. Roscoe, F.R.S. (Wm. Collins, Sons, & Co.)
[2] Van Helmont's science was, however, of an extremely rudimentary nature, as may be evidenced by the belief he entertained that the smells which arise from the bottom of morasses produce frogs, slugs, leeches, and other things; as well as by the following recipe which he gave for the production of a pot of mice: "Press a dirty shirt into the orifice of a vessel containing a little corn, after about twenty-one days the ferment proceeding from the dirty shirt, modified by the odour of the corn, effects a transmutation of the wheat into mice." The crowning point in this recipe, however, lay in the fact that he asserted that he had himself witnessed the fact, and, as an interesting and corroborative detail, he added that the mice were born full-grown. See 'Louis Pasteur: His Life and Labours.' By his Son-in-law. Translated by Lady Claud Hamilton. (Longmans, Green, & Co.) P. 89.
[3] He then goes on to relate a number of experiments by Cornelius Drebel and Albertus Magnus, showing the refreshing power of this balsam, and then those of Quercitan with roses and other flowers, and his own with nettles.
[4] Priestley, however, did not realise that carbonic acid gas was a necessary plant-food; on the contrary, he considered it to have a deleterious action on plant-growth. Percival was really the first to point out that carbonic acid gas was a plant-food.
[5] It is recorded as an instance of the scientific enthusiasm of the man, that he was wont to carry about with him bottles containing oxygen, which he had obtained from cabbage-leaves, as also coils of iron wire, with which he could illustrate the brilliant combustion which ensued on burning the latter in oxygen gas.
[6] For a full account of Sénébier's researches, see 'Physiologie végétale, contenant une description des organes des plantes, et une exposition des phénomenes produits par leur organisation, par Jean Sénébier.' (5 tomes. Genève, 1800.)