EVOLUTION OF THE PLOW
The plow has undergone important developments in comparatively recent years. Wooden plows were still in use in America in Revolutionary times; usually the point was shod with wrought iron. However, these wooden plows speedily gave way to metal when iron came to be manufactured in considerable quantity in this country. A plow has to contend with two conditions of service that apparently conflict with each other. The constant friction of the soil against the blade tends to wear it away very rapidly, hence a very hard surface is requisite. On the other hand, the plow is apt to encounter buried stones and rocks which will shatter it unless it is soft. The problem then is to make the plow both hard and soft. The chilled iron plow was invented by Oliver, in 1855, to meet the first condition. When molten iron is poured into an iron mold the surface that comes into contact with the mold is suddenly chilled, producing a very hard surface that takes a good polish. This effect is accentuated by using a hollow mold through which water is circulated. The hard surface of the chilled iron wears well in sandy and gravelly soil, it does not rust deeply, and it clears well in sticky soil. However, it is very brittle and is liable to break if struck a sharp blow. A more recent improvement is the soft-center steel plow. This is both hard and soft. It is composed of three layers of metal; the outer layers are of hard cast steel and the center one of soft steel. These metal layers are heated to a welding heat and then rolled together, producing a plow that has a hard outer wearing surface and at the same time is tough because the center layer of soft steel acts as a cushion to absorb sharp blows. To increase the wearing qualities of the plow still further a patch of very hard cast steel is welded over the point of the share. Thus both conflicting requirements of softness and extreme hardness are met.
We think of the plow as a very simple tool, but the modern implement is a product resulting from a vast amount of study and research into the materials most suitable for its construction and into the best form of share and moldboard. In place of a single plow for all purposes the modern farmer is offered a large assortment to suit various classes of work. At least three different kinds of plows are indispensable on every farm; the sod plow, the stubble plow, and the corn-cultivating plow. The sod plow is used for turning over the sod and breaking the clod. This is provided with a jointer or diminutive plow point set above the share, which turns over the edge of the furrow to prevent grass from growing up between the furrows. The stubble plow has a moldboard with less twist than that of the sod plow. This is used for plowing land that was under cultivation during the previous year.
The plow of to-day has become more than a hand-guided, horse-drawn tool. It has developed into a real machine, mounted on wheels, with a disk or coulter wheel that cuts the furrow cleanly, means for leveling the plow and regulating the depth of the plow, and a seat for the plowman. It works upon soil with the same precision that a planer works upon a slab of cast iron. The furrow is neatly sliced, lifted, and turned over with mechanical accuracy. As the furrow slice slides over the moldboard of the plow the soil is pulverized by friction. The front furrow wheel runs in the furrow previously cut which serves as a track to guide the machine. The front and rear furrow wheels are inclined from the vertical so as to balance the thrust of the plow and they may be given a lead toward or from the “land” or unplowed part of the ground to regulate the steering automatically. The proper adjustment and balancing of a plow calls for considerable skill.
Agricultural operations are now conducted on such a vast scale that the single plow cannot begin to do the necessary work. Instead, sets of gang plows are used so that from a dozen to two dozen furrows may be turned at a time. Steam or gasoline tractors of the wheel or track-laying type are required to furnish the tractive effort needed to haul these huge plows. The larger tractors are so powerful that they haul not only the plow but a harrow behind the plow to break up the clods and a seeder behind the harrow to sow and cover the seed so that all three operations are performed simultaneously.
The disk type of plow is used in very dry and hard soil and also in very sticky soil. A rolling disk takes the place of the moldboard and share, and in this way friction is reduced very materially, with the result that less tractive effort is required to draw the machine.
There is scarcely any agricultural operation for which a machine has not been designed. We cannot attempt to describe them all. For tilling the soil there are plows, harrows, drags, and rollers of many different varieties; for seeding and planting there are grain and seed drills, corn planters, potato planters, etc.; for cultivating or working the growing crops there are cultivators, weeders, fertilizer drills, corn plows, etc.; and for harvesting or gathering the crops there are mowers, hay rakes and tedders, reapers and binders, potato diggers, corn binders and huskers, corn shellers, etc.