. The human body and health : an elementary text-book of essential anatomy, applied physiology and practical hygiene for schools . If, therefore, some bits ofwood be heated very hot in a claypipe while the top of the bowl iscovered with wet clay to keep out theair, the gases will go out through thestem, and as they issue may be lightedwith a match. After fifteen minutesheating, carbon, called charcoal, is leftin the pipe. In a similar way gas forlighting houses was formerly made byheating soft coal in iron boxes. Hydrogen.—This is present in nearlyall foods and composes two thirds ofwater. It
. The human body and health : an elementary text-book of essential anatomy, applied physiology and practical hygiene for schools . If, therefore, some bits ofwood be heated very hot in a claypipe while the top of the bowl iscovered with wet clay to keep out theair, the gases will go out through thestem, and as they issue may be lightedwith a match. After fifteen minutesheating, carbon, called charcoal, is leftin the pipe. In a similar way gas forlighting houses was formerly made byheating soft coal in iron boxes. Hydrogen.—This is present in nearlyall foods and composes two thirds ofwater. It is a colorless gas, and maybe easily made by pouring some weaksulphuric acid into a bottle containinga few nails or tacks. The iron pushesoff the hydrogen, which forms partof the acid, and the gas appears inbubbles (Fig. 17). It will pass outof a glass tube inserted through thecork, and will burn when a flame isapplied to it. This burning is theunion of the hydrogen with the oxygen of the air. As aresult water made of hydrogen and oxygen is appears in drops on a bottle held upside down atthe top of the Fig. 17. — Making hydro-gen. The bottle con-tains five nails andweak sulphuric the right of theflame of hydrogen atthe tip of the glass tubeare two drops of waterformed by the unionof the hydrogen com-ing out of the bottleand the oxygen in theair. PROPERTIES OF OXYGEN 31 Oxygen. — This is a colorless and odorless gas whichconstitutes one fifth of the air, one third of the water, andabout one fifth of the solid portion of all living lifeless compounds contain it. Oxygen may easily be prepared by heating together ina test tube black oxide of manganese and chlorate of pot-ash. To catch thegas, arrange a bentglass tube with itsone end through thecork in the test tubeand the other pass-ing just within themouth of a bottlefilled with waterand turned upsidedown in a dish ofwater (Fig. 18).The bottle is filledwith water at firstto expel the a
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