. The principles of chemistry . the gasholder into the cylinder through b. 17 When it is required to prepare hydrogen in large quantities for filling balloons,copper vessels or wooden casks lined with lead are emi^loyed ; they are filled with scrapiron, over which dilute sulphuric acid is poured. The hydrogen generated from a numberof casks is carried through lead pipes into special casks containing water (in order to coolthe gas) and lime (in order to remove acid fumes). To avoid loss of gas all the joints aremade hermetically tight with cement or tar. In order to fill his gigantic balloon (o
. The principles of chemistry . the gasholder into the cylinder through b. 17 When it is required to prepare hydrogen in large quantities for filling balloons,copper vessels or wooden casks lined with lead are emi^loyed ; they are filled with scrapiron, over which dilute sulphuric acid is poured. The hydrogen generated from a numberof casks is carried through lead pipes into special casks containing water (in order to coolthe gas) and lime (in order to remove acid fumes). To avoid loss of gas all the joints aremade hermetically tight with cement or tar. In order to fill his gigantic balloon (of25,000 cubic metres cajmcity), Giftard, in 1878, constructed a complicated apparatus forgiving a continuous supply of hydrogen, in which a mixture of sulphuric acid and waterwas continually run into vessels containing iron, and from which the solution of ironsulphate formed was continually drawn off. When coal gas, extracted from coal, isemployed for filling balloons, it should be as light, or as rich in hydrogen, as Ilu. 23.—Gasholder. THE COMPOSITION OF AVATER, HYDROGEN 129 Hydrogen, besides being contained in water, is also contained inmany other substances,^^ and may be obtained from them. As examplesof this, it may be mentioned (1) that a mixture of formate of sodium,CHNaOo, and caustic soda, NaHO, when heated to redness, formssodium carbonate, ISTaoCOa, and hydrogen, H.,; >^ (2) that a number oforganic substances are decomposed at a red heat, forming hydrogen,among other gases, and thus it is that hydrogen is contained in ordinarycoal gas. Charcoal itself liberates hydrogen from steam at a high tempera-ture ; 20 ii3ut the reaction which here takes place is distinguished by acertain complexity, and will therefore be considered later. The properties of hydrogen.—Hydrogen presents us with an exampleof a gas which at first sight does not differ from air. It is not sur-prising, therefore, that Paracelsus, having discovered that an aeriformsubstance is obtain
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