CHAPTER VI TTHE COMPOUNDS OF NITROGEN WITH HYDROGEN AND OXYGEN

mixed with oxygen and immediately shaken up with caustic potash, it is almost entirely converted into potassium nitrite; whilst after a certain time, when the formation of nitric peroxide has already commenced, a mixture of potassium nitrite and nitrate is obtained. If oxygen is passed into a bell jar filled with nitric oxide, brown fumes of nitrous anhydride and nitric peroxide are formed, even in the absence of moisture; these in the presence of water give, as we already know, nitric acid and nitric oxide, so that in the presence of an excess of water and oxygen the whole of the nitric oxide is easily and directly converted into nitric acid. This reaction of the re-formation of nitric acid from nitric oxide, air, and water, 2NO + H 2 O + O 3 = 2HNO 3 , is frequently made use of in practice. The experiment showing the conversion of nitric oxide into nitric acid is very striking and instructive. As the intermixture of the oxygen with the oxide of nitrogen proceeds, the nitric acid formed dissolves in water, and if an excess of oxygen has not been added the whole of the gas (nitric oxide), being converted into HNO 3 , is absorbed, and the water entirely fills the bell jar previously containing the gas. It is evident that nitric oxide in combining with oxygen has a strong tendency to give the higher types of nitrogen compounds, which we see in nitric acid, HNO 3 or NO 2 (OH), in nitric anhydride, N 2 O 5 or (NO 2 ) 2 O, and in ammonium chloride, NH 4 Cl. If X stand for an atom of hydrogen, or its equivalents, chlorine, hydroxyl, &c., and if O, which is, according to the law of substitution, equivalent to H 2 , be indicated by X 2 , then the three compounds of nitrogen above named should be considered as compounds of the type or form NX 5 . For example, in nitric acid X 5 = O 2 + (OH), where O 2 = X 4 , and OH = X; whilst nitric oxide is a compound of the form NX 2 . Hence this lower form, like lower forms in general, strives by combination to attain to the higher forms proper to the compounds of a given element. NX 2 passes consecutively into NX 3 —namely, into N 2 O 3 and NHO 2 , NX 4 (for instance NO 2 ) and NX 5 .