A very instructive experiment is performed by heating a good mass of tartrate of lead in a glass tube which is hermetically sealed, and being placed on an iron support, is then covered by a capped air jar with a sliding rod and stamper, the whole being arranged in a plate containing water. When the stamper is pushed down upon the glass the latter is broken (Fig. 107), and the air gradually penetrates to the finely divided lead, when ignition occurs, and the oxygen is absorbed, as demonstrated by the rise of the water in the jar. On the same principle, if a bottle is filled about one-third full with a liquid amalgam of lead and mercury, and then stopped and shaken for two hours or more, the finely divided lead absorbs the oxygen and leaves pure nitrogen. Or if a mixture of equal weights of sulphur and iron filings, is made into a paste with water in a thin iron cup, and then warmed and placed under a gas jar full of air standing on the [Page 105] shelf of the pneumatic trough, or in a dish full of water, the water gradually rises in the jar in about forty-eight hours, in consequence of the absorption of the oxygen gas. _Third Experiment._ Nitrogen is devoid of colour, taste, smell, of alkaline or acid qualities; and, as we shall have occasion to notice presently, it forms an _acid_ when chemically united with oxygen, and an alkali in union with hydrogen. A lighted taper plunged into this gas is immediately extinguished, while its specific gravity, which is lighter than that of oxygen or air, is demonstrated by the rule of proportion. Weight of 100 cubic Weight of 100 cubic Specific inches of air at 60° Unity. inches of nitrogen at gravity of Fahr., bar. 29.92 in. 60° Fahr., bar. 29.92 in. nitrogen. 30.829 : 1 :: 29.952 : 971