Elementary lessons in the physics Elementary lessons in the physics of agriculture . elementarylesson01king Year: 1894 127 most such soils are extremely minute, 153, and often contain much silica. In Fig. 51 is represented a type of one of the most successful plows for this class of soils. In form it resem- bles the breaking-plow, and the surface of the mold-board is very hard and susceptible of a high polish. The hard surface in these plows appears to be demanded to prevent it from be- coming roughened by the scratching of hard soil particles; the less abrupt curvature of the mold-board dimi
Elementary lessons in the physics Elementary lessons in the physics of agriculture . elementarylesson01king Year: 1894 127 most such soils are extremely minute, 153, and often contain much silica. In Fig. 51 is represented a type of one of the most successful plows for this class of soils. In form it resem- bles the breaking-plow, and the surface of the mold-board is very hard and susceptible of a high polish. The hard surface in these plows appears to be demanded to prevent it from be- coming roughened by the scratching of hard soil particles; the less abrupt curvature of the mold-board diminishes the surface pressure and thus the liability to scratching, w^hile the fine polish furnishes the fewest and shallowest depressions into which the extremely minute particles can be wedged by the pressure. It is a matter of great moment, in the care of such plows, that they be kept from rusting, because this quickly destroys the necessary polish. 199. Pulverizing Function of Plows.—The stubble plows are constructed so as to pulverize the soil at the time it is being overturned. This action of the plow can best be ap- preciated by taking a thick bunch of paper, like the leaves of a book, and bending it abruptly upon itself; when this is done it will be observed that the leaves slide upon one another, and through a greater distance the more abruptly the bending takes place. The steep mold-board of the full-stubble plow shown in Fig. 47 has this shearing action upon the soil as one of its chief functions and this necessarily increases its draft. In selecting plows for the naturally mellow soils where pul- verizing is unessential, the type represented in Fig. 50 should be taken, as, other conditions being the same, its draft will be lighter. 200. Driving Three Horses Abreast.— Much time and expense can be saved in plowing by driving three horses abreast, using a larger plow or a gang of plows, and this method is especially to be commended on all clear land where there is an
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