The valve should be lifted occasionally from the seat to prevent grooving, and to redistribute the abrasive, and then dropped back, after which the grinding should proceed as before. Remove the valve after it turns without friction, wipe it clean, apply fresh oil and emery and grind once more. When the grinding has removed all pits and ridges, and presents a smooth even surface, the grinding is complete. To test for accuracy of grinding place a little Prussian Blue on the seat, if the valve is ground to a perfect surface the blue will show uniformly spread over the seat, if the grinding is incomplete bare places showing high spots will be seen. It is a good plan to finish the grinding by using a little Tripoli with oil after the emery has removed the pits and high spots, as Tripoli is finer than emery and will smooth down scratches made by the emery. After the grinding has been performed to your satisfaction, wash the valve, valve stem, and guides thoroughly with gasoline and kerosene to remove the smaller traces of emery, to prevent wear and cutting. When the valves are ground in place on the engine stuff up all openings or parts of the cylinder to prevent the emery from gaining access to the bore. After grinding is complete wipe off surfaces thoroughly and remove waste used for stuffing. CHAPTER XIII TRACTORS AND FARM POWER Because of our increased population, which results in a greater planted acreage, and the scarcity and increased cost of farm labor, farming has rapidly developed into an industrial science. Where formerly the farmer was content to perform certain parts of his work by hand, he today employs machinery for the same task, and is far more particular as to the working of his soil and the cost of production per acre. By the use of machinery his crop is marketed at less expense, in a shorter time, and he has more time in which to enjoy life than ever before. The modern gasoline and oil engine has been the greatest factor contributing to the farmer’s ease and prosperity for it has eliminated the terrors and drudgery of plowing, churning, watering stock, sawing wood, threshing, and has besides given him many of the conveniences of city life, such as running water and electric light. The benefits of power are not only conferred on the farmer but his wife as well for the small domestic engines have saved the back of the house wife during the strenuous period of harvest time.