OXYGEN J 



CHEMISTRY. 



sia 



OXYGEX. 



THIS elementary body is of the utmost importance in 

 the economy of nature. It forms |ths of all water on 

 the face of the globe. The atmosphere which we breathe 

 contains one-fifth of its bulk of oxygen ; and all the earths, 

 oxides of metals, organic substances of nearly every kind, 

 have it as one of their constituents. In its entire absence, 

 the very existence of animated nature would cease. The 

 earth would become a barren wilderness : every one of its 

 productions would fail, and chaos would reign over the 

 fair face of nature once more. To its gradual combination 

 with other substances, we owe the natural heat of plants 

 and animals. When such combinations take place more 

 rapidly, we obtain our artificial heat, as in the combustion 

 of wood, coals, and other fuel. 



To its action on metals is due the development of that 

 wonderful agent, Electricity, as seen in voltaic batteries, 

 vad in the vast laboratory of the mineral kingdom. All 

 -ur sources of artificial li^ht depend on it ; and, indeed, it 

 is the " one thing needful" in almost every phase of our 

 existence, happiness, an.l comfort. 



The chemist recognises its properties in the form of a 



gas ; and in this state oxygen is heavier than the air its 



specific gravity being 1 -ill air=l'000 ; it hence follows 



100 cubic inches will weigh 34 grains. Its equiva- 



hydrogen being 1-00, is 8 '00 ; and it combines, by 



volume, with that gas in producing water in the proportion 



of one of oxygen to two of hydrogen. It assumes the 



liquM or solid state when in combination with other 



bodies, as in water and the metallic oxides. 



IB following pages, we shall not follow the plan 

 nsually adopted in scientific works, because we shall 

 introduce a considerable variety of experiments, having 

 for their object the elucidation of the facts we mention. 

 In so doing, we expect that our readers wish to become 

 practically acquainted with the subject, and we shall 

 endeavour to assist them as much as possible in that 

 respect. We have already described many kinds of 

 apparatus which will be required, and shall afford de- 

 scriptions of others which may be necessary for special 

 purposes. 



Oxygen may be procured, for experimental purposes, 

 from various sources, some of which we shall fully de- 

 scribe. Amongst these are the following : 



rimeitt 5. Introduce some powdered black 

 oxide of manganese into an iron tube closed at ono end, 

 or into a gun-barrel, and into the open end of either 

 vessel fit a pewter tube, so that its other end may dip 

 beneath water. Apply heat, as of a common fire-place, 

 to that part of the iron tube containing the manganese. 

 After a short time, a quantity of gas will be given off, 

 which, on being collected by means of the pneumatic 

 trough and gas jars,* will be ready for experimental 

 purposes. 



When a large quantity of oxygen is required, a mercury 

 bottle and bent tube are used ; the vessel being but half 

 filled with the oxide of manganese. The arrangement 

 has already been described, together with a convenient 

 kind of gas-holder, t 



Experiment 6. Into a small-sized glass retort,}; 

 introduce some of the black oxide of manganese, and 

 then add sufficient strong sulphuric acid to make the 

 whole of a thick creamy consistence. Rest the bulb of 

 the retort on a ring-stand, and allow its stem to dip 

 below the water in a pneumatic trough. Apply a gentle 

 heat to the mixture, and in a short time oxygen will be 

 pi ven off, which may be collected in the usual manner. 

 The mode of conducting this and similar processes for 

 making gases, is illustrated in the following engraving ; 

 in which, however, a bent tube is added to the stem of 

 the retort, instead of dipping it beneath the water in the 

 trough. 



Oxygen may be obtained by heating other metallic 

 oxides, Ac. ; but the following mode is always ad|>t,-.l 

 when very pure oxygen is required ; aud unless the gas 



9e antr, p. 304 ; fig. 9. 

 t Ante, p. SOS ; Fig. L 

 VOD I. 



t A'nt^, p. 304 ; Fi*. 12 and 13. 

 t Ante, p. 3(16 ; Fig. 3J. 



is wanted in very large quantities, it is altogether, per- 

 haps, the beat source for all purposes. 

 Fig 35. 



Experiment 7. Mix one part of chlorate of potass 

 with half its weight of black oxide of manganese : in- 

 troduce this into a retort, and apply the heat of a spirit- 

 lamp or gas-furnace. In a short time the whole mass 

 will become incandescent, and oxygen will be rapidly 

 given off, which may be collected in the usual way. 

 Some little care is required, as if too great a heat be 

 suddenly applied, the gas is given off witli so much 

 violence as to become unmanageable. By means of the 

 mercury bottle aud this mixture, we ha~e frequently 

 made thirty cubic feet in less than half-an-hour. 



We should here warn those of our readers who are 

 unacquainted with the nature of chlorate of potass, that 

 although by itself it is a perfectly harmless substance, it 

 gives rise to dangerously explosive substances when 

 mixed with other articles. Amongst these are sulphur, 

 phosphorus, and sulphuric acid ; and, to a slighter extent, 

 many organic substances, such as sugar, <tc. , have a 

 similar effect. It should therefore be kept by itself ; 

 and to prevent any risk of admixture, the experi- 

 mentalist should make a considerable quantity of the 

 mixture of the salt and oxide of manganese, which he 

 may keep by him, ready for use, in a glass bottle. This 

 may be labled " oxygen mixture ;" and when wo use 

 this term in our future pages, it will be in reference to 

 this compound. 



In heating the mixture, the oxide of manganese is not 

 decomposed. It merely affords points of contact, by 

 means of which the heat spreads more rapidly through 

 the salt, and saves time. That such is effected, may 

 be noticed by the following experiment. 



Experiment 8. Heat some chlorate of potass alone 

 in a small retort or test-tube, ntted with a bent tube, 

 by means of the spirit-lamp. The salt will melt, and 

 will give off oxygen slowly. 



Instead of retorts, a Florence flask and bent tube|| 

 may always be employed. This is the most economical 

 mode of procedure, as the fracture of the flask is of no 

 consequence, from its trifling value. It is well that our 

 readers should diminish, as much as possible, the ex- 

 penses of their experiments; and, at the same time, 

 thereby acquire a knack of substituting one arrangement 

 for another. 



By heating nitre in a similar manner to that adopted 

 with chlorate of potass, oxygen may be obtained. 

 There is, however, one objection to this plan ; which is, 

 that a considerable quantity of nitrogen is given off at 

 the same time ; which, of course, injures its purity. 

 Another source of oxygen, which is necessarily quite 

 pure, is that of the decomposition of water by means of 

 voltaic electricity, which has been already fully de- 

 scribed ;1T but the practical difficulties and expense* 

 preclude its us.e in ordinary circumstances. 



A sufficient quantity of oxygen having been prepared, 

 and collected in gas jars or bottles,** the following ex- 

 periments may be tried, which will exhibit some of its 

 leading properties. 



Experiment 9. Dip a lighted taper into a jar of 



|| See ante, p. 304 ; Fig. 3. H Anl Section 3, " Electricitj." 



Ante, p. SW ; Fig. 8. 



2s 



