Probably more than nine-tenths of the fertilizers used in this country are purchased in the form of mixtures containing all three of the essential constituents, nitrogen, phosphorus, and potassium. The various brands are prepared from formulas designed to be especially suitable for different crops and soils. This method of purchase saves labor and thought on the part of the farmer, but the cost of the constituents is greater than if the fertilizer materials are bought and home-mixed; besides, in the mixtures the farmer does not always obtain such proportions of the constituents as are best adapted to his conditions. These mixed fertilizers, as a rule, are, and should always be, accompanied by a statement of guaranteed composition. This is very essential, because purchasers are unable to tell, by mere visual inspection, what kinds and proportions of fertilizing materials have entered into the mixture. In many states the laws require that the source of the materials also shall be distinctly stated, in order to insure the use of good products, as the mixing permits the disguising of poor forms, especially of those containing the element nitrogen.

Guarantees, however, sometimes confuse the purchaser, because the method of stating the guarantee is such as to mislead, provided he does not understand the meaning of the terms, or is unable to convert the percentages into their equivalents. It is entirely legitimate, when there are no laws forbidding, for the manufacturer to guarantee ammonia, instead of nitrogen; bone phosphate, instead of phosphoric acid; and sulfate of potash, instead of actual potash. The statement of the guarantee of the constituents in combination increases the percentage, thus leading ignorant purchasers to think that they are obtaining a larger percentage of the constituents than is really the case.

In the case of raw materials, a guarantee based on the purity of the chemical salts is very frequently used. That is, a substance when pure contains 100 per cent of the specific salt, and the guarantee which accompanies this product is merely a statement that indicates its purity. For example, when nitrate of soda is guaranteed to contain 95 per cent nitrate, it means that it is 95 per cent pure nitrate, or that 5 per cent of the total substance consists of impurities. The same is true in the case of sulfate of ammonia, sulfate of potash, muriate of potash, and other potash salts that may be offered. In order that the farmer may have a simple method of determining the actual content of the constituents, however guaranteed, the following tables are given to show the terms that are used, their equivalent of actual elements, and the factors to use in converting the one into the other: —

Fertilizer Formulas and Guarantees Voorhees 23

The following statements show the methods of stating guarantees on the basis of purity, in the case of many raw materials, and the equivalent percentage on the basis of actual constituents: Guarantee on basis of purity: —

Nitrate of soda, 95 per cent, or containing 95 per cent pure nitrate. Muriate of potash, 80 per cent, or containing 80 per cent pure muriate. Sulfate of potash, 98 per cent, or containing 98 per cent pure sulfate. Kainit, 25 per cent, or containing 25 per cent pure sulfate.

Guarantee on basis of actual constituents: —

Nitrate of soda, total nitrogen..........    15.64 per cent.

Muriate of potash, actual potash.........    50.50 per cent.

Sulfate of potash, actual potash .........    53.00 per cent.

Kainit, actual potash.............    13.50 per cent.

The following illustration shows a guarantee of the same mixed fertilizer, on the basis of equivalents in combination, and on the basis of actual constituents: Guarantee on basis of equivalents in combination: —

Nitrogen (equivalent to ammonia), 2 to 3 per cent.

Available phosphoric acid (equivalent to bone phosphate of lime), 16 to 20 per cent. Potash (equivalent to sulfate of potash), 6 to 8 per cent.