262 SCIENTIFIC AMUSEMENTS. 



carbon dioxide gas will escape vigorously (Expt. 99) and gradually 

 fill the basin. Blow a soap bubble with cold air from a bladder, 

 or render one blown by the breath slightly heavier than air by 

 attaching to it a light car, as in Expt. 307, so that it will sink 

 when detached from the blowing pipe ; let it fall on to the centre 

 of the basin of carbon dioxide, when it will remain suspended, 

 floating on the sea of heavy gas in the basin, just as a hollow india- 

 rubber ball would on the surface of a tub of water (fig. 115). 



7. Effects of Heat upon Bodies other than Change of 

 State and Production of Chemical Action. 



CHAPTER XIX. 

 EXPANSION AND CONTRACTION. 



When a body becomes warmer it generally becomes larger, 

 although there are some exceptions to this rule ; the ascent of the 

 quicksilver in a thermometric tube on heating it has already been 

 explained (Expt. 28) to be due to the fact that whilst the glass 

 case becomes larger or expands by heat, the quicksilver expands 

 more rapidly, and therefore occupies more space. 



Expt. 310. To show that Metals Expand on Heating. A 

 simple arrangement for showing this consists of a brass or copper 

 ball (fig. 116) suspended by a wire and turned to such a size that 

 when cold it will just drop through a horizontal ring fixed so as 

 to stand on three legs. Heat the ball for a short time in the 

 flame of a Bunsen lamp or spirit lamp ; it will then be found too 

 large to pass through the ring. If left a while standing on the 

 ring it will by and by drop down through it, partly because as it 

 cools it becomes smaller, and partly because the ring becomes 

 heated by touching it, and consequently expands and becomes 

 wider. Fig. 117 represents another arrangement for illustrating 

 the same thing, consisting of a bar of metal with a gauge of such 

 size that the bar can just fit in when cold, but is too large to do 

 so when hot. 



Fig. 118 illustrates an arrangement for making a determination 

 of the amount of increase in the length of a bar when it is 

 heated ; a bar of metal (t) is held in a flame in such a way that 

 one end is firmly clamped by a screw (v) whilst the other presses 



