Let us assume that the field contains enough nitrogen, but other needs remain the same. In such case, the nitrogen is dropped out, and the application becomes 250 pounds per acre. The home-mixer may substitute tankage of guaranteed analysis for part of the nitrogen and phosphoric acid. Let us assume that the tankage runs 9 per cent nitrogen and 20 per cent phosphoric acid. If half the required nitrogen per acre, or 4-1/2 pounds, is wanted in tankage, 50 pounds of the tankage will supply it. At the same time the 50 pounds of tankage supplies 10 pounds of phosphoric acid, replacing one third of the 214 pounds of acid phosphate. We thus have for the acre 30 pounds of nitrate of soda, 50 pounds of tankage, 143 pounds of acid phosphate, and 36 pounds of potash, or 259 pounds. The content of plant-food remains the same, but one half of the nitrogen is only slowly available. The farmer who buys unmixed materials will incline to use only a few kinds, and at first he will confine himself chiefly to materials whose composition varies little. In this way he quickly sees in a ton of the material, not the whole bulk, but the definite number of pounds of nitrogen and other constituents of plant-food contained in it, and the calculations in home-mixing become simple. Materials that should not be Combined.--The advocate of factory-mixed goods warns the farmer against the danger of making combinations of materials that will cause loss by chemical action. The danger is wholly imaginary if no form of lime, wood-ashes, or basic slag is used in the home-mixtures. As has been said, some materials will harden, if permitted to absorb moisture, and if the mixture must stand, a few hundred pounds of muck or dry road dust should be added to each ton as a drier, and a correspondingly larger amount per acre should be applied. Making a Good Mixture.--The process of mixing is simple, and careful station tests have shown that it is fully as effective as factory-mixing. The unmixed materials should be kept in a dry place until the mixing is done. If there are any coarse lumps, a wooden tamper can crush them on the barn floor, and the material should be passed through a sand-screen. The material of largest bulk should be spread on the floor, and the other materials should be put on in layers. Three careful turnings with a shovel will secure good mixing. Scales should be used to secure accuracy in desired amounts of the materials.