CHEMISTRY. 



Nitrates and nitrites occur in the soil. The 

 mode of their formation will be considered unde 

 Ammonia. Hydrated nitric acid can be obtainec 

 by heating any nitrate (most commonly, nitrate o 

 soda the cheapest nitrate is used) with sulphuric 

 acid (see p. 309). All the other oxides of nitrogen 

 are most easily prepared from hydrated nitric acid 

 Peroxide of nitrogen is a reddish-brown vapour 

 having an extremely irritating action on the lung 

 when even a small quantity of it mixed with mucl 

 air is breathed. It can be condensed to a brown 

 liquid, nearly colourless when cooled to a lov 

 temperature. It is formed I. By the reduction 

 of nitric acid as when hydrated nitric acid acts 

 on tin, the tin unites with part of the oxygen 

 forming an oxide ; and red fumes are given off 

 consisting of peroxide of nitrogen. 2. By the 

 decomposition of some nitrates by heat for 

 instance, nitrate of copper, CuO,N 2 O 5 , when 

 heated, gives cupric oxide, CuO, which remains 

 behind ; while, instead of anhydrous nitric acic 

 being given off, we have peroxide of nitrogen anc 

 free oxygen, CuO,N 2 O 6 = CuO + 2NO 2 + O. 

 3. By the union of nitric oxide and oxygen. 

 Nitric oxide, NO, when mixed with oxygen, at 

 once combines with it, forming peroxide of nitro- 

 gen. 



Nitrous acid is produced in various reductions 

 of nitric acid for instance, when hydrated nitric 

 acid acts on white arsenic, or on starch. It is a 

 reddish-brown vapour, closely resembling peroxide 

 of nitrogen. It can be condensed to a blue 

 liquid. When nitrate of potash, K 2 O,N 2 O 5 or 

 KNO 3 , is strongly heated, it loses oxygen, and 

 yields nitrite of potash, K 2 O,N 2 O 3 or KNOg. 



Nitric oxide is a colourless, transparent gas, 

 very sparingly soluble in water. It has not been 

 condensed to the liquid state. It is formed by the 

 reduction of nitric acid for instance, when hy- 

 drated nitric acid acts on some metals (copper, 

 lead, mercury, silver), an oxide of the metal is 

 formed, which at once unites with nitric acid to 

 form a nitrate, and nitric oxide gas is given off. 

 Its most remarkable character is its action on 

 oxygen gas. When these two colourless gases 

 are mixed, they instantly combine to form red 

 fumes of peroxide of nitrogen. 



Nitrous oxide is a colourless transparent gas, 

 having a sweetish taste. Water, at ordinary 

 temperatures, dissolves about its own volume of 

 the gas. It can be condensed by cold and pres- 

 sure to the liquid state, and may be frozen to an 

 ice-like solid by very intense cold. This gas 

 supports the combustion of most ordinary com- 

 bustibles, such as wood, paper, wax, &c. the 

 oxygen combining with the combustible, and the 

 nitrogen becoming free. It cannot, however, sup- 

 port animal life, as the oxygen is too firmly held 

 by the nitrogen to be given up to the red colouring- 

 matter of the blood. At the same time, it is not 

 directly poisonous, and can be breathed for a 

 short time without injury. When so breathed, it 

 produces insensibility, and is now used in minor 

 surgical operations for the same purposes as 

 chloroform or ether. In small quantities, it pro- 

 duces intoxication, whence its popular name, 

 laughing-gas. Its preparation will be described 

 under Ammonia. 



The only known substance consisting solely of 

 nitrogen and hydrogen is ammonia. Ammonia is 

 a colourless, transparent gas, having a peculiar 

 21 



pungent odour. Its specific gravity is 0-59. It is 

 very soluble in water, one volume of water absorb- 

 ing, at ordinary temperatures and pressures, be- 

 tween 600 and 700 volumes of the gas. Solution 

 of ammonia is specifically lighter than water : it 

 gives up the whole of the ammonia when boiled. 

 This solution is what is sold as ' liquor ammonia?,' 

 or 'spirit of hartshorn.' The gas can be con- 

 densed by cold and pressure to a colourless 

 liquid. 



Ammonia is composed of 14 parts by weight of 

 nitrogen, and 3 of hydrogen : its formula is NH 3 . 

 It unites with the hydrated acids or hydric salts 

 to form ammonia salts. Thus, ammonia unites 

 with hydrochloric acid to form the salt known 

 as sal-ammoniac NH 3 + HC1 = NH 3 ,HC1 or 

 NH 4 C1; with nitric acid to form nitrate of 

 ammonia NH 3 + HNO 3 = NH 3 ,HNO 3 or 

 NH 4 NO 3 ; with sulphuric acid it unites in two 

 proportions to form acid sulphate of ammonia, or 

 bisulphate of ammonia, and normal sulphate of 

 ammonia NH 3 + H 2 SO 4 = NH 3) H 2 SO 4 or 

 NH 4 HS0 4 , and 2NH 3 + H 2 SO 4 = 2 NH 3 ,H 2 SO 4 

 or (NH 4 ) 2 SO 4 . These ammonia salts resemble 

 very closely, in crystalline form and in many 

 chemical characters, the corresponding potash 

 salts ; and if we compare the formulae of the two 

 sets of salts, we see that there is also an analogy 

 in composition : 



NH 4 C1; NH 4 N0 3 ; NH 4 HSO 4 ; (NH^SO^ &c. 

 KC1; KN0 3 ; KHSO 4 ; KjSO^ &c. 



The reader will at once see that wherever we have 

 in a potash salt K (that is, 39 parts of potassium), 

 in the corresponding ammonia salt we have NH 4 

 (that is, 17 parts of ammonia and i of hydrogen). 

 NH 4 is, therefore, a compound radical (see p. 313), 

 and stands to K in a relation similar to that of 

 NO 3 to CL This compound radical has received 

 the name of ammonium : thus, sal-ammoniac, 

 NH 4 C1, is chloride of ammonium, &c. There are 

 some points where the analogy between potas- 

 sium and ammonium breaks down. We may com- 

 pare this analogy to that between a firm or cor- 

 poration and an individual person. In buying 

 and selling, in borrowing and lending, in suing or 

 n being sued, a corporation or firm resembles 

 an individual ; but there are cases where this 

 resemblance totally ceases those cases, namely, 

 which lead to the dissolution of the firm, or the 

 surrender of the charter of the corporation. So 

 n the case of ammonium and potassium, in a 

 great many double decompositions, the actions 

 of the ammonium salts resemble those of the 

 )otassium salts ammonium (NH^ in the one 

 :ase, and potassium (K) in the other, chang- 

 ng place with other metals ; but sometimes the 

 ammonium breaks up, and its constituents take 

 each its separate course. It is by a reaction of 

 his kind that pure ammonia is prepared. Anhy- 

 [rous potash), K,O, and hydrated or caustic, 

 K 2 O,H 2 O (or KHO), are compounds of potassium 

 which have no analogues in the ammonium set 

 There is no (NH 4 ),O, and no NH 4 HO.* Every 

 hemical change which might be expected to pro- 

 luce either of these bodies really yields ammonia 

 nd water (NH 4 ) 2 O becoming; 2NH 3 + H 2 O, 

 nd NH 4 HO becoming NH 3 +H 2 O. Thus, when 



* The formula NH 4 HO and the name hydrated oxide of am- 

 lonium are sometimes used, but they do not refer to a definite 

 ubstance, but merely to ammonia and water acting together. 



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