High-grade Fertilizers.--A high-grade fertilizer is not necessarily a high-priced one. What we want in a fertilizer is a high content of the plant-food needed, together with desirable availability. If only phosphoric acid is wanted, a 14 per cent, or 16 per cent, acid phosphate is high-grade because it contains as many pounds of available phosphoric acid in a ton as the public can buy in a large way. A 10 per cent acid phosphate is low-grade. The effort is to escape paying freight, and other cost of handling, on waste material as far as possible. Generally speaking, the higher the percentages of plant-food in a fertilizer, the cheaper per pound is the plant-food. A low-grade fertilizer rarely fails to be an expensive one because the expense of handling adds unduly to the price per pound of the small content of plant-food. CHAPTER XIX HOME-MIXING OF FERTILIZERS The Practice of Home-mixing.--The business of compounding fertilizers has been involved in a great deal of unnecessary mystery. Many of our best station scientists have labored to show that the home-mixing of fertilizers is a simple and profitable piece of work, and the heaviest users of fertilizers in the east now buy unmixed materials, but a majority of farmers use the factory-mixed. Manufacturers are right in their contention that many people do not know what materials are best for their own fields, or what proportions are best, but the purchase of mixed materials does not solve their problem and it does not help them to a solution as quickly as home-mixing. The source of the plant-food in the factory-mixed goods is not known, while it is known in the home-mixed. Effectiveness of Home-mixing.--Van Slyke says ("Fertilizers and Crops," p. 477): "Manufacturers of fertilizers and their agents have persistently sought to discourage the practice of home-mixing, but their statements cannot be accepted as the evidence of disinterested parties. It has been represented to farmers that peculiar and mysterious virtues are imparted to the plant-food constituents by proper mixing, and that really proper mixing can be accomplished only by means not at the command of farmers. Such statements are misrepresentations, based either upon the ignorance of the person who makes them or upon his determination to sell commercial mixed goods." Criticisms of Home-mixing.--The manufacturer's advocate formerly laid much stress upon the danger attending the treatment of bones and rock with sulphuric acid. That is a business of itself, and the home-mixer has nothing to do with it. He buys on the market the acidulated bone or rock, just as a manufacturer makes his purchase.