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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Color Pictures of Mineral Defeciencies in Plants
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