Ingredients in the Mixture.--The matters of interest to the farmer are the determination of the amounts of nitrogen, phosphoric acid, and potash that he should apply to a particular field, their availability, and their cost. Let us assume that he has found 300 pounds of a fertilizer containing 3 per cent nitrogen, 10 per cent phosphoric acid, and 6 per cent potash to be an excellent application for wheat on a thin soil that is to be seeded to clover and timothy. This fertilizer contains 3 pounds of nitrogen to each 100 pounds. He applies 300 pounds of the fertilizer per acre, or 9 pounds of nitrogen. The fertilizer contains 10 pounds of phosphoric acid to the 100 pounds. He thus applies 30 pounds of phosphoric acid per acre. The fertilizer contains 6 pounds of potash per 100 pounds, and he therefore applies 18 pounds per acre. What he has really learned, then, is that an acre of this land, when seeded to wheat, needs 9 pounds of nitrogen, 30 pounds of phosphoric acid, and 18 pounds of potash. It is in these terms he should do his thinking, and the matter of fertilization becomes simple. In the general farming of the Pennsylvania experiment station, it is the practice to depend upon nitrate of soda as the source of a fertilizer for wheat. Manufacturers claim that sulphate of ammonia and tankage would be better. The farmer soon will learn what he prefers for his soil, provided he practices home-mixing. Let us assume that he uses nitrate of soda, which never varies much from 15 per cent in its content of nitrogen. If 100 pounds of nitrate contain 15 pounds of nitrogen, the 9 pounds wanted for an acre will be found in 9/15 of 100 pounds or 60 pounds. Thirty pounds of phosphoric acid are wanted for an acre. If the acid phosphate contains 14 per cent of phosphoric acid, or 14 pounds to the 100, the required amount will be 30/14 of 100, or 214 pounds. Eighteen pounds of potash are wanted for an acre. The muriate of potash on our markets never varies much from 50 per cent in its content of potash. If 100 pounds of muriate contain 50 pounds of potash to the 100, the required amount wanted will be 18/50 of 100, or 36 pounds. Adding the 60, 214, and 36 pounds, we have 310 pounds for the acre of land. If the field contains 20 acres, the order will call for 20 times the 60 pounds of nitrate of soda, 20 times the 214 pounds of acid phosphate, and 20 times the 36 pounds of potash. If the farmer prefers to use sulphate of ammonia, which varies little from 20 per cent of nitrogen, or 20 pounds in the 100, he will get his 9 pounds of nitrogen for an acre by buying 9/20 of 100 pounds, or 45 pounds, and the substitution of the 45 pounds of sulphate of ammonia for the 60 pounds of nitrate of soda will reduce the total application of fertilizer per acre from 310 pounds to 295 pounds. The important fact is that in either case there is the required amount of nitrogen.