Fill a deep glass jar with carbonic acid, and ascertain its presence with a lighted taper; if a beaker glass to which a string is attached is let down into the vessel and drawn up, and then inverted over a lighted [Page 159] taper, the utility of this simple plan is at once rendered apparent; the beaker glass represents the empty bucket, and can be let down and pulled up full of carbonic acid until a sensible change in the condition of the atmosphere is produced. The best plan, however, is to set the air in motion by heat obtained from burning matter, or even a kettle of boiling water, lowered by a cord, and this fact is well shown by putting a small flask full of boiling water, and corked, at the bottom of the deep glass jar containing the carbonic acid gas, which rises like other gases when sufficiently heated, and passing away, mixes with the surrounding air. (Fig. 149.) [Illustration: Fig. 149. A. Deep jar containing carbonic acid gas, which is being removed by the little glass bucket. B. Jar containing corked flask of boiling water on a pad; the heated gas rises and the cold air descends to take its place.] _Thirteenth Experiment._ Carbonic acid gas dissolved in water under considerable pressure, forms that most agreeable drink called soda-water; the gas is not only useful in this respect, but has been applied most successfully by Mr. Gurney to extinguish a fire on a gigantic scale, which had been burning for years in the waste of a coal mine in Scotland. The same gas, generated suddenly by the combustion of a mixture of nitre, coke dust, and clay, or plaster of Paris, in vessels of a peculiar construction, has formed the subject of a patent by Phillips, since merged into the Fire Annihilator Company. The instrument is peculiarly adapted for shipping, and might, if properly used, be the means of saving many ships and valuable lives. (Fig. 150.) Its practical value is established by the test of actual use: in the streets, by the Leeds Fire Brigade, and by firemen of the Fire Annihilator Company, temporarily stationed at Liverpool and Manchester. The Fire Annihilator has been formally recognised by the Government Emigration Commissioners, who introduced into the Passengers' Act, 1852, in §24, the alternative, "_Or other apparatus for extinguishing fire_," with distinct reference to this invention, and subsequently by formal order authorized their officers to pass ships carrying Fire Annihilators. [Page 160]