112 



SCIENTIFIC AMUSEMENTS. 



other ; invert the jar, and instantly apply a light ; the hydrogen 

 will take fire and burn, possibly with a slight explosion if any air 

 is mixed with it during collection (compare Expt. 

 207), but without doing any damage. Kefill 

 the jar with hydrogen from the generator, and 

 set it again on the table, but this time mouth 

 upwards; after the lapse of a minute apply a 

 lighted taper, to the jar, when nothing whatever 

 will occur; the taper, if lowered into the jar, 

 will burn, but no firing of gas in the jar will 

 take place (provided sufficient time has elapsed), 

 because all the hydrogen will have floated up- 

 wards and escaped, its place being taken by 

 ordinary air. Balloons made of thin material, or 

 soap bubbles, filled with hydrogen will be buoyed 

 Fig. 59. Hydrogen up and ascend in the air, because of this action 

 collected by Dis- (Expt. 307). 



placement. Expt 10 6. Another Illustration. Fill a jar 



with hydrogen as before ; hold a second jar of the same size (as 

 shown in fig. 60), and pour the hydrogen upwards from the first 



jar into the second, by gradually 

 depressing the former as indicated. 

 After the jars have been thus held 

 for half a minute, separate them, and 

 apply a light to each. The gas in 

 the upper jar will burn with a slight 

 explosion, as some air is sure to have 

 got mixed with it during the trans- 

 fer ; whilst that in the lower jar 

 will not burn at all, again sho wing- 

 that the lighter hydrogen has floated upwards. 



Expt. 107. Diffusion of Hydrogen into the Air. Fill two 

 jars with hydrogen as before, and place them on a shelf in a cup- 

 board, each upon a tripod stand, mouth downwards, so that the air 

 has free access to the mouths of the jars. Apply a light to the 

 mouth of one jar, and the hydrogen will burn ; if the light be 

 applied by thrusting up a candle at the end of a wire, or a long 

 wax taper, well into the jar, the taper will light the hydrogen at 

 the mouth of the jar, but will be itself extinguished inside (fig. 

 61), because the hydrogen gas present cannot keep up the same 

 chemical changes going on in the candle flame that will take place 

 in the air. By cautiously lowering the candle again so as to with- 

 draw it from the jar slowly, it may be relit by the burning- 

 hydrogen as it emerges. 



Fig. 60. Hydrc 



upwards. 



poured 



