NITROGEN AND NITROGEN COMPOUNDS
Sources of nitrogen
We have learned that the air is composed chiefly of oxygen and nitrogen. These are not combined as oxygen and hydrogen are in water, but are simply mixed together, four-fifths of the mixture being nitrogen. Nitrogen is also found in combination in a large number of substances in nature. It is found in the nitrates, as salt-peter or potassium nitrate, KNO3, and Chili salt-peter or sodium nitrate, NaNO3. It is also found in the form of ammonia, which is a compound of nitrogen and hydrogen of the formula NH3, and exists in that form in a limited quantity of the air. In most foods, especially in those of animal origin, nitrogen occurs in chemical combination.
Properties of nitrogen
Nitrogen is a colorless, tasteless, odorless gas which does not burn, and does not combine readily with oxygen, or with any other element except at a very high temperature, and except in the formation of living plants, or in animal life. Just as nitrogen does not support combustion, so also it does not support life. An animal would die confined in a tank of nitrogen, not on account of any active poisonous properties in the nitrogen, but for lack of oxygen.
Compounds of nitrogen
When a compound containing carbon, hydrogen and nitrogen is heated in a closed vessel, so that the air is excluded, and so that it cannot burn, the nitrogen passes out of the compound, not as nitrogen, but in combination with hydrogen, which forms ammonia. Nearly all animal substances contain carbon, hydrogen, oxygen, and nitrogen, and many of them give off ammonia when heated as above described.
Why ammonia is used in making artificial ice
Ammonia is written by the chemist NH3, or one part of nitrogen gas to three parts of hydrogen. It is a colorless, transparent gas with a very penetrating, characteristic odor. In concentrated form it causes suffocation. It is but little more than half as heavy as air. It is easily converted into liquid form by pressure and cold. When pressure is removed from the liquefied ammonia, it passes back very rapidly into gaseous form, and in so doing it absorbs heat. Investigators have taken advantage of these facts and are employing liquid ammonia in the manufacture of artificial ice.