Page:The American Cyclopædia (1879) Volume XII.djvu/480

 466 NITRITES NITROGEN hot pulverized charcoal, combustion will be produced. If it is mixed with oil of vitriol and poured upon oil of turpentine, the latter will burst into a flame. It parts with its oxy- gen to phosphorus with explosive violence. It rapidly corrodes organic substances, particu- larly animal tissues, and when slightly diluted stains the skin, wool, feathers, and albuminous bodies a bright yellow. It acts with great en- ergy upon the more oxidizable metals ; gold, platinum, rhodium, and iridium alone resist its oxidizing power. Its action is most ener- getic when its specific gravity is between 1 '35 and 1-25, and the presence of nitrous acid in- creases its power. The action of nitric acid upon metals is not so simple as that of sul- phuric acid, whose components are held to- gether with stronger affinities. According to one view, when sulphuric acid unites with a metal, the latter first becomes oxidized by com- bining with the oxygen of the water, while the hydrogen is set free. Another and later opin- ion is that the metal simply displaces the hy- drogen from its union with the sulphion, SC>4, thus : HSO 4 + M = MSO 4 + H. When nitric acid is employed, the metal in the same way displaces the hydrogen from its union with the nitrion (NO 3 ), but hydrogen is not evolved, because it instantly unites with oxygen derived from decomposing acid or its lower oxides. The mode of action varies with the metal acted upon and other circumstances. When silver is dissolved in the cold in an excess of diluted nitric acid, nitrous acid (HNO 2 ) is formed, and there is no evolution of gas. If the solution is warm, the action is more violent, and nitric oxide (N0 2 ) is disengaged, or a similar effect may be obtained by employing a more oxi- dizable metal, as copper or mercury. When the acid is pretty strong (sp. gr. 1-4), peroxide of nitrogen is disengaged, and by raising the temperature free nitrogen is also evolved, the acid undergoing complete deoxidation. A metal having a stronger affinity for oxygen, as zinc, will cause the evolution of nitrous oxide; and when the acid is concentrated ammonia is one of the products, and may be found combined with the excess of acid. The principal uses of nitric acid are in the manufacture of nitrates of the metals and of sulphuric acid, where it completes the process of oxidation by furnish- ing an addition equivalent to the sulphurous acid. (See SULPHURIC ACID.) NITRITES, salts produced by the union of nitrous acid with bases; general formula, MNO 2. The principal metallic salts are those of potassium, sodium, barium, ammonium, cop- per, lead, and nickel. The nitrites of lead form an interesting series, but are of more professional than general interest; and the same remark applies to the double potassium nitrites with other metals. The nitrites are usually prepared by reducing the nitrates. Ni- trite of potassium and of soda may be ob- tained by decomposing potassic nitrate at a red heat, dissolving the residue in water, crystalli- zing out the remaining nitrate, and evaporating. The alcoholic nitrites, or nitrous ethers, are bodies of great interest, to the physiologist as well as chemist. The principal are the nitrites of amyl, ethyl, methyl, and butyl. The ni- trite of amyl (C 6 HiiNO 2 ) is an inflammable liquid, of a fruity pear-like odor, reddish yel- low color, and specific gravity 0-877, boiling at 196. It may be prepared by passing ni- trous vapors into amylic alcohol in a gently heated retort, rectifying the distillate, and col- lecting those portions going over at 196. When inhaled it acts as a powerful stimulant to the heart, the excitement being followed by greatly diminished power of the organ and contrac- tion of the external vessels. It suspends the respiration of animals, but the effect may be stopped short of death, the result being a state resembling trance. The appearance after death differs with the mode of administration. If the nitrite is given rapidly, the lungs and brain are found free from congestion, and the left side of the heart empty, but the right cavities will be engorged. When administered slowly, the lungs and brain are congested and both sides of the heart contain blood. Nitrite of ethyl, or nitrous ether, CaHsNOa (formerly- called nitric ether, saltpetre, and naphtha), was first observed by Rumkel in 1681, but its composition was first exactly determined by Dumas and Boullay. It is prepared by distil- ling a mixture of equal parts of alcohol and nitric acid, a gentle heat being applied at the commencement. The distillate is received in a series of Woulf's bottles half filled with salt water. The nitrous ether collects on the surface of the brine. It is a yellowish liquid, having the odor of apples, sparingly soluble in water, but perfectly so in all proportions in alcohol. It boils at 62, and has a specific gravity of 0-947. It is decomposed by the action of caustic potash into nitrite of po- tassium and alcohol. The sweet spirits of nitre of pharmacy is a solution of nitrous ether, aldehyde, and several other substances, prepared by distilling 3 Ibs. of alcohol with 4 Ibs. of nitric acid. Nitrite of methyl (CH 3 NO 2 ) is prepared by treating wood spirit with nitric acid and copper turnings. When a liquid, it has a specific gravity of 0*991, and boils at 11 F. Its smell resembles that of nitrous ether. Ni- trite of butyl (C4H 9 NO 2 ) has been employed by Tyndall with advantage in experiments upon polarized light. NITROGEN (Gr. virpov, nitre, and yevvaeiv, to generate), an elementary gaseous body, form- ing about four fifths of the bulk of the atmos- phere. It derives its name from being also an essential constituent of nitre. It was dis- covered by Rutherford in 1772, but its prop- erties were more particularly investigated by Lavoisier in 1775, and also by Scheele about the same time. Lavoisier estimated the pro- portion contained in the atmosphere, and gave it the name of azote (Gr. a privative and. w#, life), because it is incapable of supporting