CHAPTER VI TTHE COMPOUNDS OF NITROGEN WITH HYDROGEN AND OXYGEN

case is termed the solution of metals by acids, although it is not a case of simple solution, but a complex chemical change of the substances taken. When treated with this acid, those metals whose oxides do not combine with nitric acid yield the oxide itself, and not a salt; for example, tin acts in this manner on nitric acid, forming a hydrated oxide, SnH 2 O 3 , which is obtained in the form of a white powder, Sn + 4NHO 3 = H 2 SnO 3 + 4NO 2 + H 2 O. Silver is able to take up still more oxygen, and to convert a large portion of nitric acid into nitrous anhydride, 4Ag + 6HNO 3 = 4AgNO 3 + N 2 O 3 + 3H 2 O. Copper takes up still more oxygen from nitric acid, converting it into nitric oxide, and, by the action of zinc, nitric acid is able to give up a still further quantity of nitrogen, forming nitrous oxide, 4Zn + 10NHO 3 = 4Zn(NO 3 ) 2 + N 2 O + 5H 2 O. Sometimes, and especially with dilute solutions of nitric acid, the deoxidation proceeds as far as the formation of hydroxylamine and ammonia, and sometimes it leads to the formation of nitrogen itself. The formation of one or other nitrogenous substance from nitric acid is determined, not only by the nature of the reacting substances, but also by the relative mass of water and nitric acid, and also by the