MATERIALS EXISTING IN WATER. 35 



every nine parts bj weight of water converted into steam 

 and decomposed, one part of hydi-ogen escapes as gas, while 

 eight parts of oxygen enter into combination with the iron of 

 the tube. 



32. Hydrogen gas, as has already been mentioned (14), 

 unites with nitrogen to form ammonia, and constitutes 

 three pounds in every 17 lbs. of that compound. It is, 

 like oxygen, destitute of colour, taste, or smell. It has not 

 been found in nature except in combination with some other 

 body. It is most inflammable, though, strange to say, not 

 capable of supporting combustion: thus, if we fill a bottle 

 with this gas and introduce into it a lighted candle, the flame 

 will be extinguished, but the gas itself, where it is in contact 

 with the air at the mouth of the bottle, will take fire and hum 

 with a pale yellow fiame, so that the candle will be relighted as 

 we withdraw it from the bottle.* Oxygen gas, it will be 

 remembered, possesses properties exactly the reverse of those 

 just described; it is, unlike hydrogen, a powerfal supporter 

 of combustion but cannot itself be inflamed. 



33. Hydrogen gas is the lightest body in nature, a hun- 

 dred cubic inches of it weighing only about 2\ grains, while 

 the same quantity of air would weigh 30 grams ; therefore 



* Hydrogen gas may be conveniently prepared by placing some cut- 

 tings of the metal zinc, or even a few iron nails in a bottle, furnished with 

 a tube as before described, and pouring upon them some oil of vitriol 

 ililuted with three or four times its bulk of water ; the water is decom- 

 posed, and hydrogen gas separates from it, escaping through the tube, 

 and may be collected in a vessel over water, or in a bladder provided 

 with a stop-cock. It may even be prepared, when no proper apparatus 

 can be procured, by placing the materials described in a common ale 

 i^lass, and covering the glass with the hand or a piece of moistened card 

 pai>er to detain the gas. In collecting the gas over the water-trougli, 

 so as to prevent its being mixed with the common air which the bottle 

 contains, fill a receiver twice the size of the gas Iwttle, and allow the 

 impure gas to escape before collecting for experiment. Ex. — Place in a 

 half-pint bottle about half an oz. of cuttings of zinc, half fill the bottle 

 with water, and pour in vitriol until the gas comes off briskly, then 

 dose the bottle with a sound cork through which a gas-jet or a bit of 

 the tul>e of a clay pipe has been inserted, and allow the action to go on 

 for a few minutes to ensure the escape of the common air contained in the 

 bottle ; apply a light to the jet, and the gas will inflame and continue to 

 bum with a pale yellow flame. Hold over the flame a saucer, and the 

 burning hydrogen given off from the decomposed water will seize upon 

 oxygen from the air, water will be reproduced, and the saucer will bt- 

 covered with moisture. 



c2 



