240 



NITROGEN. 



Basil Valentine, in the fifteenth century, describes 

 the process more minutely, and calls the acid 

 water of nitre. Subsequently it was colled spirits of 

 'nitre, and aquafortis. Nitric acid is prepared as fol- 

 lows : Three parts of pure nitrate of potash, coarsely 

 powdered, are to be put into a glass retort, with two 

 of strong sulphuric acid. To the retort is united a tu- 

 bulated receiver, and heat is applied to the retort by 

 a sand bath. The first product that passes into the 

 receiver is generally red and fuming, but these ap- 

 pearances soon subside, and the acid comes over pale, 

 and even colourless. After this it again becomes 

 more red and fuming, till the end of the operation. 

 The acid obtained, provided the process be carefully 

 conducted, will have a specific gravity of 1-5 ; and 

 acid of this density may be obtained, amounting to 

 two-thirds of the weight of the nitre employed. The 

 receiver requires to be refrigerated by cold water or 

 ice. When a strong nitric acid is not the object, but 

 it is intended simply to manufacture the common dilute 

 acid, called, in commerce, aqua fortis, less sulphu- 

 ric acid, in proportion to the nitre, will suffice : 100 

 parts of good nitre, sixty of strong sulphuric acid, 

 and twenty of water, form economical proportions. 

 Nitric acid, having a specific gravity 1 -5, contains 

 nearly eighty-six per cent, of acid, and fourteen of 

 water. It has been formed by electrizing, for a great 

 length of time, a mixture of oxygen and nitrogen 

 gases, in the proportion by measure, of five parts of 

 oxygen to three of common air, or seven of oxygen to 

 three of nitrogen, or common air by itself. A little 

 water is contained in the tube, holding potash in so- 

 lution which, after the experiment, becomes convert- 

 ed into nitrate of potash, This experimeut was first 

 performed in 1785, by Mr Cavendish, who inferred 

 from it that nitric acid is composed of oxygen and 

 nitrogen. Nitric acid, as obtained in the laboratories 

 of the arts, frequently contains portions of sulphuric 

 acid and of muriatic acid. The former is derived 

 from the acid which is used in the process, and the 

 latter from sea-salt, which is frequently mixed with 

 nitre. These impurities may be detected by adding a 

 few drops of a solution of muriate of barytes, and nitric 

 of silver, to separate portions of nitric icid, diluted 

 with three or four parts of distilled water. If the 

 muriate of barytes cause a cloudiness or precipitate, 

 sulphuric acid must be present ; if a similar effect be 

 produced by nitrate of silver, the presence of muriatic 

 acid may be inferred. Nitric acid is purified from 

 sulphuric acid by redistilling it from a small quantity 

 of the nitrate of potash, with the alkali of which the 

 sulphuric acid unites and remains in the retort. To 

 separate the muriatic acid, it is necessary to di op a solu- 

 tion of nitrate of silver into the nitric acid as long as a 

 precipitate is formed, and draw off the pure acid by 

 distillation. Nitric acid possesses acid properties in 

 an eminent degree. It unites with and neutralizes 

 alkaline substances, forming with them salts, which 

 are called nitrates. When of a specific gravity of 15, 

 it emits dense, white, suffocating fumes, if exposed to 

 the air, from which it attracts moisture, and experi- 

 ences a diminution in its density and strength. A 

 rise of temperature is occasioned by mingling it with 

 water in a certain proportion. From its strong 

 affinity for water, it occasions snow to liquefy with 

 great rapidity. It boils at 248 Fahr., and may be 

 distilled without suffering material change. It may 

 be frozen at about 50 below zero : when diluted with 

 half its weight of water, it becomes solid at 1^ F. 

 Nitric acid acts powerfully on substances which are 

 disposed to unite with oxygen ; and hence it is much 

 employed by chemists for bringing bodies to the 

 maximum of oxidation. Nearly all the metals are 

 oxidized by it, and some of them, such as tin, copper, 

 and mercury, are attacked with great violence. If 



flung on burning charcoal, it increases the brilliancy 

 of its combustion in a high degree. Sulphur and 

 phosphorus are converted into acids by its action. 

 All vegetables are decomposed by it. In general, 

 the oxygen of the nitric acid enters into direct com- 

 bination with the hydrogen and carbon of those 

 compounds, forming water with the first, and car- 

 bonic acid with the second. This happens remark- 

 ably in those compounds in which hydrogen and 

 carbon are predominant, as in alcohol and the oils. 

 It effects the decomposition of animal matters also. 

 The cuticle and nails receive a permanent yellow 

 stain when touched with it; and, if applied to the 

 skin in sufficient quantity, it acts as a powerful cau- 

 tery, destroying the organization of the part entirely. 

 When oxidation is effected through the medium of 

 nitric acid, the acid itself is commonly converted into 

 the deutoxide of nitrogen, which is sometimes evolved 

 in a state of purity, bat more commonly mingled with 

 nitrous oxide and nitrous acid gases. The direct 

 solar light deoxidizes nitric acid, resolving a portion 

 of it into oxygen and nitrous acid. When the vapour 

 of nitric acid is transmitted through red-hot tubes, it 

 suffers complete decomposition, and a mixture of 

 nitrogen and oxygen gases is the product. Nitric 

 acid is of considerable use in the arts. It is employed 

 for etching on copper ; as a solvent of tin, to form 

 with that metal a mordant for some of the finest 

 dyes ; in metallurgy and assaying, in various chemi- 

 cal processes, on account of the facility with which 

 it parts with its oxygen and dissolves metal ; in 

 medicine as a tonic, as also in the form of vapour to 

 destroy contagion. For the purposes of the arts, it 

 is commonly used in a diluted state, and contaminated 

 with the sulphuric and muriatic acids by the name of 

 aqua fortis, two kinds of which are found in the shops, 

 one called double aqua fortis, which is about half 

 the strength of nitric acid ; the other simply aqua 

 fortis, which is half the strength of the double. A 

 compound made by mixing two parts of the nitric 

 acid with one of muriatic, known formerly by the 

 name of aqua regia, and now by that of nitro-mtiriatic 

 acid, has the property of dissolving gold and platina. 

 On mixing the two acids, heat is given out, an effer- 

 vescence takes place, and the mixture acquires an 

 orange colour. Nitrogen combines with chlorine 

 and iodine to form two very remarkable compounds. 

 The first of these, the chloride of nitrogen, is formed 

 by the action of chlorine on some salt of ammonia. 

 Its formation is owing to the decomposition of ammo- 

 nia (a compound of nitrogen and hydrogen) by chlo- 

 rine : the hydrogen of the ammonia unites with 

 chlorine and forms muriatic acid, while the nitrogen 

 of the ammonia, being presented in its nascent state 

 to chlorine dissolved in the solution, enters into com- 

 bination with it. The chloride of nitrogen is formed 

 gradually, when a glass receiver, filled with chlorine 

 gas, is inverted over a bowl containing a solution of 

 muriate of ammonia, and falls in little globules 

 through the fluid to the bottom of the dish, whence 

 it is withdrawn with the utmost care by means of a 

 glass syringe. On being injected into a metallic 

 mortar, or leaden dish containing a little volatile oil, 

 or phosphorus in small pieces, it detonates with ex- 

 treme violence. Its specific gravity is 1.653: it is 

 not congealed by the intense cold produced by n 

 mixture of snow and salt; may be distilled at 160 

 Fahr., but explodes at a temperature between 200 

 and 212. It consists of chlorine 144, or four pro- 

 portions ; nitrogen, 14, or one proportion. 



Iodide of nitrogen. From the weak affinity that 

 exists between iodine and nitrogen, these substances 

 cannot be made to unite directly ; but, when iodine 

 is put into a solution of ammonia, the alkali is decom- 

 posed ; its elements unite with different portions of 



