NITROGEN

1353

NITROGEN-GATHERING CROPS

water, and is an intensely corrosive liquid, which is colorless when pure, but, is usually colored yellow by the presence of lower oxides of nitrogen, 'it fumes in the air, colors the skin yellow, producing painful burns, and usually dissolves or oxidizes all the commoner metals except gold and platinum, with the violent expulsion of choking, red fumes. Aluminum is dissolved but slowly by it, and in some instances the strong acid must be diluted with water before it will act upon a metal. Dilute nitric acid is generally less active the more water it contains. Strong nitric acid, mixed with sulphuric acid, acts upon cotton and glycerine to form the explosives, guncotton and nitroglycerin. Nitric acid is extensively used in chemical operations, particularly to dissolve metals and to oxidize substances. When the metals or their oxides or carbonates dissolve in this acid, salts called nitrates are produced. Mixed with hydrochloric acid, nitric acid forms agua regia (royal water), which is capable of dissolving gold and other substances that are not attacked by a single acid. Nitric acid is also used to some extent in medicine.                    Horace L. Wells.

Ni'trogen is an elementary gas which in the free state forms nearly four fifths by volume of our atmosphere. In combination with other elements, nitrogen is a necessary constituent of all plants and animals, and it forms a very large number of important compounds, both natural and artificial. Its presence in the atmosphere was discovered in 1772 by Rutherford, at that time professor of botany in the University of Edinburgh. It was more particularly investigated soon after by Priestley, Scheele, Cavendish and Lavoisier. It is a colorless, tasteless, odorless gas, and was formerly regarded as permanent and incondensable; but it can be liquefied at a sufficiently low temperature. Nitrogen is slightly lighter than, atmospheric air, and is fourteen times as heavy as hydrogen. It is but slightly soluble in water, one hundred volumes of water at ordinary temperature dissolving only one and a half volumes of nitrogen.

While nitrogen is a constituent of all plant and animal organisms and of many important compounds, it is, in a free state, rather inert toward other elements and does not readily enter into direct combination with them. It is not combustible, nor does it act in the atmosphere as a supporter of combustion, as a lighted taper plunged into a jar of nitrogen will at once be extinguished. Nitrogen is not poisonous, since it is breathed freely along with oxygen by all animals; but it cannot support life, and an animal placed in it will die from suffocation for want of the oxygen necessary for breathing. Its function in the atmosphere seems to be mainly that of diluting the oxygen with which it is there associated. Although nitrogen forms about 79.1 per cent.

of the total volume, and 77 per cent, of the total weight, of the atmosphere, the free gas cannot be taken up by plants directly, but it is combined with other elements through the agency of certain bacteria that exist in nodules on the roots of leguminous plants, that is, those that are related to clover, peas etc. Other plants, particularly grasses and grains which require much nitrogen, are dependent upon the combined nitrogen of the soil; hence nitrogenous fertilizers, such as dried blood, ammonium salts and nitrates, as well as ordinary manures, are important in agriculture for use on soils containing insufficient nitrogen. Two of the important compounds of nitrogen are nitric acid and ammonia. This element also is an essential constituent of the proteids or albuminoids, which make an important part of our food, as well as of the alkaloids, most of the dyes and a host of other natural and artificial compounds.                              H. L. Wells.

Nitrogen-Qathering Crops all belong to the family of leguminous plants or Legu-minosece, having irregular, conspicuous flowers or clusters and seeds in pods. The bean and pea are good examples. The clovers do not seem at first sight to answer this description. All have abundant foliage, root deeply, and are remarkable for their ability to take pure nitrogen from the soil and store it up m form available as plant and animal food. This is done by means of germ-like organisms which grow inside of tiny lumps on the roots. These nodules can be seen by washing the earth from the roots of any of these plants, and range in size from that of a pin-head to that of a. small pea. These nodules will not appear on clover roots if none of the germs exist in the soil. Such a soil can now be inoculated with the germs by applying a solution containing them. The germs are put up in dry form like yeast-cakes and can be obtained from the Department of Agriculture, and be dissolved to make the solution. The nitrifying action goes on best in well-ventilated soils. In poorly drained soils just the opposite process, denitrification, is apt to occur, reducing plant food to unavailable simple nitrogen. The subject of nitrifying bacteria is very complex, as they possibly also exert a fermenting influence on the minerals of the soil. Experiments have shown that an acre of cowpeas at the Louisiana Experiment Station produced 65 pounds of nitrogen, and an acre of crimson clover at Cornell University produced 156 pounds, 30 of which were in the roots. Other clovers produce a greater proportion in the roots, as the mammoth clover, with 78 pounds in the roots out of a total of 146 pounds. It grows best in wet soils that usually are deficient in nitrogen, and so leaves much in the soil when the tops are cut off. Red clover, the usual variety grown on loams and heavier clays, contained,