Paper prepared with sulphate of manganese is an excellent test for ozone, and changes brown rapidly by the oxidation of the proto-salt of manganese, and its conversion into the binoxide of the metal. Ozone is also prepared by pouring a little sulphuric ether into a quart bottle, and then, after heating a glass rod in the flame of the spirit lamp, it may be plunged into the bottle, and after remaining there a few minutes ozone may be detected by the ordinary tests. NITROGEN, OR AZOTE. [Greek: _Nitron_], nitre; [Greek: _gennaô_], I form; [Greek: _a_], privative; [Greek: _zôê_], life. Symbol, N; combining proportion, 14. Also termed by Priestley, _phlogisticated_ air. In the year 1772, Dr. Rutherford, Professor of Botany in the University of Edinburgh, published a thesis in Latin on fixed air, in which he says:--"_By the respiration of animals healthy air is not merely rendered mephitic_ (i.e., charged with carbonic acid gas), _but also suffers another change. For after the mephitic portion is absorbed by a caustic alkaline lixivium, the remaining portion is not rendered salubrious; and although it occasions no precipitate in lime-water, it nevertheless extinguishes flame and destroys life._" Such is the doctor's account of the discovery of nitrogen, which may be separated from the oxygen in the air in a very simple manner. The atmosphere is the great storehouse of nitrogen, and four-fifths of its prodigious volume consist of this element. [Page 103] _Composition of Atmospheric Air._ Bulk. Weight. Oxygen 20 22.3 Nitrogen 80 77.7 --- ---- 100 100. The usual mode of procuring nitrogen gas is to abstract or remove the oxygen from a given portion of atmospheric air, and the only point to be attended to, is to select some substance which will continue to burn as long as there is any oxygen left. Thus, if a lighted taper is placed in a bottle of air, it will only burn for a certain period, and is gradually and at last extinguished; not that the whole of the oxygen is removed or changed, because after the taper has gone out, some burning sulphur may be placed in the vessel, and will continue to burn for a limited period; and even after these two combustibles have, as it were, taken their fill of the oxygen, there is yet a little left, which is snapped up by burning phosphorus, whose voracious appetite for oxygen is only appeased by taking the whole. It is for this reason that phosphorus is employed for the purpose of removing the oxygen, and also because the product (phosphoric acid) is perfectly soluble in water, and thus the oxygen is first combined, and then washed out of a given volume of air, leaving the nitrogen behind. _First Experiment._