Basic Slag.--When iron ores contain much phosphorus, its extraction by use of lime gives a by-product in the making of steel that has agricultural value. The ores of the United States usually do not give a slag sufficiently rich in phosphorus to be valuable. Nearly all the basic slag used as a fertilizer is imported from Germany, and usually contains 17 to 18 per cent of phosphoric acid. The availability of the plant-food in this fertilizer has been the subject of much discussion. The chemist's test which is fair for acid phosphate is admittedly not fair when used for basic slag. Field tests, at experiment stations and on farms, are our best sources of knowledge. When the soil is slightly acid, each 1 per cent of phosphoric acid in the slag appears to be about as valuable as each 1 per cent of the available phosphoric acid in an acid phosphate. Some of the effectiveness may be due to the lime, although very little of it is in forms regarded as valuable for the correction of soil acidity. There is evidence that basic slag favors clover. It has not been found feasible to ship this material many hundreds of miles inland from the seaboard to compete with acid phosphate, but it is an excellent source of phosphoric acid for soils that are not rich in lime. Muriate of Potash.--The mines of Stassfurt, Germany, contain an inexhaustible supply of potash in various compounds. Muriate of potash is prepared from the crude salts, and the commercial product on our markets has the appearance of a coarse and discolored salt. It is handled in large bags, and inclines to become moist by absorption of water from the air. It contains some common salt. The content of actual potash is about 50 per cent. The potash is readily available, but the loss from leaching out of the soil is very small. Muriate of potash is our cheapest source of potash, and should be used for all staple crops except tobacco, sugar beets, and, possibly, the potato. Tests even on heavy soils fail to show any injury to the quality of the potato, and on light soil the muriate may always be used. Sulphate of Potash.--Some sulphate of potash is imported into this country. Its content of potash may vary 1 or 2 per cent below or above 50. Its physical condition favors mixing more than does the muriate. It usually costs several dollars a ton more than the muriate, and the fact that it is known to favor quality in tobacco, and is popularly supposed to do so in the potato, creates demand at the higher price. It is soluble in water, and quickly available. As a rule, it has no higher agricultural value than the muriate.