HYDROGEN. 



257 



FlG - 33. bottom of the bottle, and is ter- 



minated externally by a funnel 

 for introducing the acid, whilst the 

 other is the exit tube, by which 

 the hydrogen escapes. With an 

 ounce or two of zinc in it, the 

 bottle is two-thirds filled with 

 water, and the undiluted acid 

 added from time to time by the 

 funnel, so as to sustain a con- 

 tinued effervescence. No gas es- 

 capes by the funnel tube, as its 

 extremity within the bottle is 

 always covered by the fluid. To produce large quantities, a 

 half-gallon stone- ware jar may be mounted as a gas bottle, 

 with a flexible metallic pipe fitted to the cork, as the exit tube. 

 This gas may be collected, like oxygen, either in jars over 

 the pneumatic trough, or in the gas-holder. The first jar or two 

 filled will contain the air of the gas-bottle, and therefore must 

 not be considered as pure hydrogen. One ounce of zinc is 

 found to cause the evolution of 615 cubic inches of hydrogen. 



Properties. Hydrogen gas thus prepared is not absolutely 

 pure, but contains traces of sulphuretted hydrogen and carbonic 

 acid, which may be removed by agitating the gas with lime- 

 water or caustic alkali. It has also a particular odour, which 

 is not essential to hydrogen, as the gas evolved from the amal- 

 gam of sodium, acted on by pure water without acid, is per- 

 fectly inodorous. An oily compound of carbon and hydrogen, 

 which appears to be the cause of this odour, may be separated 

 in a sensible quantity from the gas prepared by iron, by trans- 

 mitting it through alcohol. Of the pure gas, water does not 

 dissolve more than 1| per cent, of its bulk. Hydrogen has 

 never been liquefied by cold or pressure. 



Hydrogen is the lightest substance in nature, being sixteen 

 times lighter than oxygen, and 1 4.4 times lighter than air ; 

 100 cubic inches of it weigh only 2.14 grains. Soap bubbles 

 blown with this gas ascend in the atmosphere ; and it is used, 

 as is well known, to inflate balloons, which begin to rise when 

 the weight of the stuff of which they are made and the hydrogen 

 together, are less than the weight of an equal bulk of air. A 

 light bag is prepared for making this experiment in the chamber, 



