tion of the soil. Of course it does not follow that no returns are secured from plant food applied under unfavorable conditions, though full returns cannot be secured under such circumstances. Good plant food is wasted, and the profit possible to be derived is largely reduced."-Voorhees.

What Are Commercial Fertilizers?-When it was first discovered that certain of the elements found in the soil are necessary to plant growth it naturally occurred to the agricultural investigators that it might be possible to renew the fertility of worn out soils by supplying these elements artificially. In the first experiments conducted along this line all the elements which the plant derives from the soil were supplied. As the investigations progressed it was discovered that increased production resulted in most instances from the addition of only three of these substances—i. e., nitrogen, phosphoric acid and potash. In other words, it was determined that except in rare cases all the other elements exist in the soil in quantities sufficient to supply the needs of the plant, even when the available nitrogen, phosphoric acid and potash are practically exhausted. For this reason it is generally considered unnecessary to supply any of the elements of plant food except the three named above, and these substances have come to be known as the "essential ingredients of a fertilizer," and the only ones that give the fertilizer a commercial value.

All Fertilizers Made From a Few Basic Materials. -From what has been said it will be seen that any material that supplies one or more of these "essential ingredients" may be used as a commercial fertilizer,

provided it could be purchased at a price that would make its use profitable. As a matter of fact, the number of substances that are available for this purpose is somewhat limited, owing to the prohibitive prices which the others bring on the market. Many persons seem to think that there is something mysterious about the manufacture of fertilizers and some of the makers encourage this belief by pretending that they have some secret process of manufacture that enables them to produce a better product than their competitors, and far better than the farmer can mix himself.

The truth is that there are a limited number of basic materials from which all the different brands of fertilizers are made, and these basic substances are articles of commerce and can be purchased by anyone. The so-called "complete fertilizers" consist of two or more of these substances mixed together in the proportion to give the required per cent of nitrogen, phosphoric acid, and potash in the finished product. Some of these materials are commonly purchased unmixed, while others are rarely seen by the farmer except as one of the ingredients of a complete fertilizer. Some of these basic materials contain only one of the essential ingredients of a fertilizer, while others contain two, but usually one is in such excess that the substance is used chiefly to furnish that one element. It is possible, therefore, to separate the basic fertilizers into three classes, viz.,

1. Materials used chiefly as sources of nitrogen.

2. Materials used chiefly as sources of phosphoric acid.

3. Materials used chiefly as sources of potash.

In order to discuss intelligently the subject of commercial fertilizers it will be necessary to consider briefly the substances included in these different classes.

NITROGENOUS FERTILIZERS

The larger number of the materials of this class are composed of various kinds of refuse animal matter from the packing houses, soap and glue factories, etc. Only those in common use will be discussed here.

Dried Blood. As its name signifies, this is the blood from the slaughter house rapidly dried by artificial heat and when ready for sale is in the form of a powder. Two grades of dried blood are found on the market known as the red and the black blood. The red blood is more carefully dried, and is not charred as is likely to be the case with the black blood, which is more rapidly dried. The red blood contains from 13 to 14 per cent of nitrogen, while the black is much less constant in composition and contains from 6 to 12 per

cent.

Meat Meal, Azotin, Ammonite.-These are synonymous terms used to designate a meat product derived principally from the rendering establishments where the different portions of dead animals are utilized. When relatively pure it contains from 13 to 14 per cent of nitrogen.

Hoof Meal. The principal source of this product is the glue factory, and it consists of the dried hoof or portions thereof ground to a fine powder. It is fairly uniform in composition and contains about 12 per cent of nitrogen.

Horn Meal is produced at the packing houses and in the factories where combs, buttons, etc., are manufactured. The chips and shavings are ground to a fine meal and sold as a fertilizer. It is quite uniform in composition, containing from 10 to 12 per cent of nitrogen, though in a very unavailable form.

Tankage consists of the dried animal wastes from the large slaughtering and rendering establishments. It is variable in composition owing to the fact that the proportions of the different ingredients of which it is composed may vary widely in different samples. As commonly made it may include offal, small bones, tendons, waste flesh, hair, etc. These materials are rendered for the extraction of the fat, and the residue is dried and ground to a meal of more or less fineness. Tankage contains phosphoric acid as well as nitrogen and the percentage of the two vary. As the nitrogen decreases the phosphoric acid increases, and vice versa. The variation of these two ingredients is so great that in trade tankage is always sold on the basis of its composition. Because it contains very considerable amounts of phosphoric acid its commercial value is not based wholly on its nitrogen content as is the case with dried blood and dried meat. Tankage contains from 4 to 9 per cent of nitrogen and from 3 to 12 per cent of phosphoric acid.

Dried Fish or Fish Guano.-Most of the fish fertilizers are made from menhaden, a fish that is caught in large numbers along the Atlantic Coast. The fish are steamed and pressed to extract the oil and the remaining "pomace" is dried and ground. This material contains from 8 to 11 per cent of nitrogen and 3

to 5 per cent of phosphoric acid. Some of the fish. fertilizers consist of the residue of the canning factories, but these are not so valuable as those derived from the menhaden.

Leather Meal consists of the smaller scraps and chips from the leather industry ground into a meal which is sometimes used in the manufacture of fertilizers. Leather is fairly rich in nitrogen, but when one takes into consideration the fact that the one object in making leather is to render it resistant to decay, it will be evident that it is not a desirable substance to use as a fertilizer.

Cottonseed Meal and Linseed Meal were formerly used as nitrogenous manures, but their value as feeds is now so well recognized that they are no longer available as fertilizers.

Peruvian and Other Guanos are composed of the accumulated droppings of fish-eating birds, more or less mixed with the dead bodies of these birds. The most important source of this material was a group of islands lying off the coast of Peru, and its high value was due to its being produced in a rainless region. Guano was formerly abundant, and was so much appreciated as a fertilizer that many substances in no way resembling the true guanos were called by that name. At the present time practically no guano of good quality is imported, and any product bearing that name should be looked upon with suspicion and purchased only upon analysis.

Sulphate of Ammonia is a by-product in the manufacture of coal gas, animal charcoal and coke. It resembles common salt somewhat in appearance, and is