468 NITRO-GLYCERINE NITZSCH of the crystalline compound, but causing in- stead the production of a green liquid, proba- bly composed of nitrous and nitric anhydride, which with water forms nitrous and nitric acids. The investigations of Playfair and Wanklyn in- dicate that the molecular constitution of per- oxide of nitrogen at low temperatures is N 2 O 4 , while at high temperatures it is N0 2 ; an opin- ion founded principally upon the great change in the specific gravity. Nitrides are combina- tions of nitrogen with the metals, and with phosphorus, boron, and silicon, without the intervention of another element. The binary combinations of nitrogen with the non-metallic elements or radicles might be considered as ni- trides, but the term is restricted as above stated. The metallic nitrides have the general formulas RN, R 2 N, R 3 N, the last being analogous to ammonia, and are all easily decomposed by heat, sometimes with explosion. They are usually formed by the action of ammonia on metallic oxides or chlorides, but may be obtained by the direct action of atmospheric nitrogen on the metals at the moment of their separation from their oxides by charcoal. Nitride of cop- per is formed by passing dry ammonia over cupric oxide at a temperature not higher than 482 F., and other metallic nitrides may be obtained in a similar way. Nitride of boron was discovered by Balmain, who obtained it by heating boric anhydride with cyanide of potassium or cyanide of zinc. The nitrides of phosphorus and silicon will be mentioned under those heads. NITRO-GLYCERINE. See EXPLOSIVES. NITRO-MURIATIC ACID, a mixture of nitric and hydrochloric acids, called by the alche- mists aqua regia, because it possesses the power of dissolving the "king of metals," gold. Both platinum and gold are insoluble in either acid separately, but are readily at- tacked by the mixture, forming chlorides. Chlorine is liberated, the action being assisted by the presence of the metal, and polarization of the molecules of the acid is produced, the chlorine in its nascent state combining with the metal. Red fumes also appear, which were at one time mistaken for peroxide of nitrogen, it being supposed that the liberated hydrogen simply deoxidized the nitric acid; but it has been found that two gases, nitric oxychloride (NO01 2 ) and nitrous oxychloride (N001), are formed instead, the former in the earlier and the latter in the later stages of the process. The action of aqua regia on metals produces perchlorides, and the oxides which may be formed by the addition of an alkali to their solutions are corresponding peroxides. NITROUS ACID. See NITROGEN. NITROUS OXIDE (N 2 O), formerly called pro- toxide of nitrogen or laughing gas, a chemical compound which may be prepared by the ac- tion of equal parts of nitric and sulphuric acid, diluted with ten parts of water, upon metallic zinc. Sulphion of the sulphuric acid unites with the metal, and the nascent hydrogen de- oxidizes the nitric acid. The reaction is rep- resented in the following equation : 8HS0 4 + 2HNO3 + 8Zn=8ZnSO 4 + 5H 2 O+N i O. The gas obtained in this way is impure, and it is better to procure it by decomposing nitrate of am- monia. The salt being placed in a retort and a gentle heat applied, it melts at 226, and at 482 or 500 is converted into nitrous oxide and water (H 4 N, NO 3 =2H 2 O + N 2 O). Nitrous oxide is a colorless transparent gas, having a specific gravity of 1*527. According to Bun- sen, 100 volumes of water at 32 dissolve 130 of the gas, at 59 77 volumes, and at 75 60 volumes. It should therefore be collected over warm water. It has a faint sweetish taste and smell. At a temperature of 45 a pressure of 50 atmospheres reduces it to a colorless liquid of specific gravity 0-9004, having a boiling point of 133. The liquid nitrous oxide mixed with sulphide of carbon and placed in vacuo caused, according to Nat- terer, a reduction of temperature to 220, the greatest degree of cold that has yet been attained. It supports combustion with a pow- er approaching that of oxygen. When respired it produces an exhilaration of the whole sys- tem, with a disposition to muscular exertion ; and there is often a state of great mental exaltation, and a disposition to uncontrol- lable laughter, from which it has received the name of laughing gas. It has the power of diminishing and destroying the sense of pain, a fact known to Sir Humphry Davy (see ANESTHETICS), and if its administration is continued of producing a state of uncon- sciousness. It is used for this purpose in the extraction of teeth, and also in surgical- operations, although sulphuric ether or chloro- form is usually preferred. NITZSCH, FTiedrich Angnst Berthold, a German theologian, born in Bonn, Feb. 19, 1832. He taught at a gymnasium in Berlin from 1857 to 1868, when he became professor of theology in the university of Giessen. His principal works are : Das System des BoetJiius (I860) ; Augus- tin's Lelire vom Wunder (1865) ; and Grund- riss der christlichen DogmengescMchte (3 vols., 1870 et seq.}. NITZSCH. I. Karl Lndwig, a German theo- logian, born in Wittenberg, Aug. 6, 1751, died there, Dec. 5, 1831. In 1781 he became preacher at Beucha, and in 1790 superinten- dent general and professor of theology in the university of Wittenberg. He resigned in 1813, and in 1817 was made director of the semina- ry for preachers in that city. He published De Itevelatione Religionis Externa eademque Publica (1808) ; De Discrimine Itevelationis Imperatorm et Didactica (2 vols., 1830) ; and Ueber das Heil der TJieologie (1830). II. Karl Inimaiuiel, a German theologian, son of the pre- ceding, born at Borna, Sept. 21, 1787, died in Berlin, Aug. 21, 1868. He received his first education at Wittenberg, studied theology un- der Schleiermacher, in 1817 became professor in v the new theological seminary at Berlin, and
