Productive farming

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1843 ...of other rocks of partially aluminous character. Potash is present in all clays, and in marl; it has been found in all aluminous earths in which it has been sought. Alum (which is a sulphate of alumina, combined with sulphate of potash) may be procured by digesting clay in sulphuric acid, which takes up both the alumina and the potash. A thousandth part of loam mixed with the quartz in red sandstone, or with the lime in the different limestone formations, affords as much petash to a soil, twenty inches in depth as is sufficient to supply a forest of pines growing upon it with potash for a hundred years. Water, impregnated with the carbonic acid of the atmosphere, decomposes rocks which contain alkalies, and then dissolves a part of the alkaline carbonates formed in the process. Plants also, by producing carbonic acid during their decay, and by means of the acids emitted by their living roots, contribute no less powerfully to destroy the coherence of solid minerals. Air, water, and changing temperature prepare the different species of rocks for yielding to plants the potash or soda they contain. Mrs. Ellis relates, that among the mountains which divide France from Spain, the rocks actually smoke after rain, under the influence of the summer sun, and become so hot that it is uncomfortable to sit down upon them. Changing temperature is a most important agent in nature. It not only assists in the original formation of soils, but exerts a most powerful influence over those already in existence. In wet soils the temperature rises slowly, and never attains the same height as in one that is sandy and dry. When the heat of the atmosphere rises no higher in the shade than 60 or 70 degrees, a dry soil may become so warm as to raise the thermometer to 90 or 100. Hence,...