atomic no. 7, atomic wt. 14.008, non-metal, row 3, col. 5A, val. 3-5, orbits 2-5

{Merck Index - © 1952 by Merck & Co., Inc.}

Nitrogen. N; at. wt. 14.008; at. no. 7; valence 3-5. Discovered in 1772 by Daniel Rutherford and independently by Scheele and Cavendish. Constitutes about 77.5% by weight or 78.06% by volume of the atmosphere; found frequently in volcanic or mine gases, gases from springs and gases occluded in minerals and rocks; an essential constituent of all living organism; fixed or combined nitrogen is present in many mineral deposits. Prepn.: Brunner, et al., cited by Mellor, A Comprehensive Treatise on Inorganic and Theoretical Chemistry, 8, 48 (1931). Vapor pressures: Dodge, Davis, J. Am. Chem. Sec. 49, 591 (1927).

Odorless gas; has been condensed to a liquid, b. –195.8° solidifies to a snow-white mass, m. –209.8°, tc = –147.1°, pc = 33.5 atm., crit. density 0.311. Sparingly soluble in water: 100 volumes of water absorbs 2.4 volumes of gas at O°, 1.6 volumes at 20°. Solubility in water at 50° to 1000 atmospheres: Wiebe et al., J. Am. Chem. Soc. 55, 947 (1933). Solubility in liquid ammonia: Wiebe, et al., ibid. 975. Solubility in alcohol: one volume of alcohol dissolves 0.1224 vol. of nitrogen at 20°. Liquid oxygen at –195.5° absorbs 50.7% of its weight of gaseous nitrogen. Heat of dissociation of the nitrogen molecule: N2 = 2N - 169.3 kcal. per g./ mol. Combines with oxygen and hydrogen on sparking forming nitric oxide and ammonia, respectively. Combines directly with lithium, and at a red heat with calcium, strontium, and barium to form nitrides. Forms cyanides when heated with carbon in presence of alkalies or barium oxide.

Use: In manufacturing ammonia, nitric acid, nitrates, cyanides, etc.; in manuf. explosives; in filling high-temp. thermometers, incandescent bulbs; to form an inert atmosphere for preservation of materials.

{Mineral deficiencies in Plants}

Nitrogen is a major constituent of several of the most important substances which occur in plants. It is of outstanding importance among the essential elements in that nitrogen compounds comprise from 40 to 50% of the dry matter of protoplasm, the living substance of plant cells. For this reason nitrogen is required in relatively large quantities in connection with all growth processes in plants. It follows directly from this that without an adequate supply of nitrogen appreciable growth cannot take place and that plants may remain stunted and relatively undeveloped when nitrogen is deficient.

Proteins, which are of great importance in many plant organs, e.g. seeds are compounds of nitrogen whilst chlorophyll, the green coloring matter of the leaves, also contain the element.

From this latter fact it will be apparent that when nitrogen is deficient leaves will contain relatively little chlorophyll, and will thus tend to be pale green in color.

In addition to the above substances, numerous other organic compounds of importance in plants, such as amino acids, amides and alkaloids, are compounds of nitrogen.

Certain compounds of nitrogen are very mobile in plants and this enables them readily to mobilize supplies of the element at vital growing points and to transfer stored supplies to points where they are most required. Such transference is common from old tissues to young growing points when supplies of the elements are short. This mobility and re-utilization of nitrogen explains why deficiency symptoms of the element always appear first in the older parts of plants and why growing points are the last to be affected.

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