110 SCIENTIFIC AMUSEMENTS. 



jar or "beaker," and half fill it with carbon dioxide from the 

 generator ; this is accomplished by passing the flexible tube to the 



bottom of the jar, and 

 testing the atmosphere 

 inside the jar with a 

 lighted candle, removing 

 the supply of gas when 

 the level of the carbon 

 dioxide is almost half- 

 way up the jar, i.e., 

 when the candle burns 

 freely in the upper part 

 of the jar, but is extin- 

 guished on lowering into 

 the lower half. Fill a 

 bladder with air, and tie 

 a tobacco pipe into the 

 mouth, and then blow a 

 soap bubble from the air 

 in the bladder (Chapter 

 Tier. 58. Pouring Carbon Dioxide from one Jar X VIIL). Shake off the 

 to another. 1111 ./ 



soap bubble from the 



pipe over the jar; the bubble, being a little heavier than air 

 when filled with cold air, not with warm breath, will descend; 

 but when it reaches the stratum of carbon dioxide in the lower 

 part of the jar, it will fall no further, but will remain apparently 

 floating half-way up the jar, because, although heavier than 

 air, the soap bubble is lighter than the same bulk of carbon dioxide, 

 and consequently behaves exactly as a cork would do if dropped into 

 a jar half full of water ; being heavier bulk for bulk than the air in 

 the upper half of the jar, the cork falls downwards through the air ; 

 but when it meets the water, being lighter bulk for bulk than water, 

 the cork falls no further, but floats on the surface of the water. 



Carbon dioxide gas is formed in Nature in a variety of ways, 

 more especially though the action of heat upon limestone and 

 similar calcareous matter underground, for which reason the gas 

 often escapes from the soil in volcanic regions ; and in consequence 

 of the decay and oxidation of vegetable matter. Moreover, during 

 fermentation of saccharine matter (Expt. 189), as in the brewing 

 of beer, and the production of wine from grape juice, &c., carbon 

 dioxide is largely formed. On account of the high density of 

 the gas, it consequently tends to accumulate in caves and hollows 

 in the earth, artificial wells and shafts of mines, brewer's vats, &c. ; 

 so that any one going down into such a cavity is liable to be 



