Some elevators are arranged to take grain slowly from under the tailboard of a wagon box. The tailrod is removed and the tailboard raised half an inch or an inch, according to the capacity of the machinery. The load pays out through the opening as the front of the wagon is gradually raised, so the last grain will discharge into the pit or elevator hopper of its own weight. Technical building knowledge and skill is required to properly connect the building and elevating machinery so that the two will work smoothly together. There are certain features about the building that must conform to the requirements and peculiarities of the elevating machinery. The grain and ear corn are both carried up to a point from which they will travel by gravity to any part of the building. The building requires great structural strength in some places, but the material may be very light in others. Hence, the necessity of understanding both building and machinery in order to meet all of the necessary technical requirements. CHAPTER V WORKING THE SOIL IMPORTANCE OF PLOWING [Illustration: Figure 132.--Heavy Disk Plow. A strong four-horse disk implement for breaking stumpy ground or to tear tough sod into bits before turning under with a moldboard.] Plowing is a mechanical operation that deals with physics, chemistry, bacteriology and entomology. The soil is the farmer's laboratory; his soil working implements are his mechanical laboratory appliances. A high order of intelligence is required to merge one operation into the next to take full advantage of the assistance offered by nature. The object of plowing and cultivation is to improve the mechanical condition of the soil, to retain moisture, to kill insects and to provide a suitable home for the different kinds of soil bacteria. There are aerobic and anaerobic bacteria, also nitrogen-gathering bacteria and nitrifying bacteria which are often loosely referred to as azotobacter species. Few of us are on intimate terms with any of them, but some of us have had formal introductions through experiments and observation. [Illustration: Figure 133.--Sulky Plow. This is a popular type of riding plow. It is fitted with a rolling coulter.] THE MECHANICS OF PLOWING