264 



SCIENTIFIC AMUSEMENTS. 



presses upon the lever and makes it move so as to register on the 

 scale (a, c) the increase in length. 



Expt. 311. Apparent Contraction on Warming. Fit into 

 the mouth of a 6 or 8 ounce flask or bottle of thin glass a perforated 

 india-rubber cork, through which a piece of quill glass tubing (a, b, 

 fig. 119) passes air-tight. Fix a paper scale 

 to the tube, take out the cork and tube, fill 

 the flask quite full with water tinted with 

 indigo, black or red ink, or other convenient 

 coloured liquid, and insert the cork again so 

 that the liquid is pressed up in the tube to 

 some convenient point on the scale, a. Pro- 

 vide a saucepan full of hot water and dip the 

 flask into it, holding it by the glass tube ; the 

 first effect of the heat will be to make the level 

 of the liquid in the stem or tube drop a 

 quarter of an inch or more, making it appear 

 as though the heat produced contraction. 

 What really takes place, however, is that the 

 heat first causes the glass to expand, so that 

 the flask becomes a little bigger and holds 

 more fluid ; after a few seconds the heat pene- 

 trates through the glass into the water and 

 causes it to expand, when the liquid begins to 

 rise in the stem towards b. On taking the 

 flask out of the hot water the opposite effects 

 are produced ; for a few seconds the water rises 

 in the stem after withdrawal, because the chill- 

 ing action of the air first affects the glass of the flask, causing it to 

 contract and squeeze the liquid upwards ; but as soon as the water 

 inside begins to cool, the liquid begins to sink again in the stem. 



Expt. 312. To show that Solids do not expand all alike. 

 Just as quicksilver and glass do not expand equally, so is there 

 observed a greater or less difference in the rate of expansion of all 

 solids. Thus bars of iron, copper, glass, and other substances, 

 when heated in the same way in the arrangement described in Expt. 

 310 (fig. 118), will cause the index to move over very different 

 amounts of space ; the increase in length which a copper rod will 

 undergo will be found to be about half as much again as that 

 indicated with an iron rod, which again will be greater than that 

 shown by a glass rod ; on the other hand, a rod of lead or zinc 

 (not heated so highly as to melt) will expand nearly twice as 

 much as one of copper heated to the same extent. 



Expt. 313. Curving of Compound Metallic Bars on Heating. 



Fig. 119. Measure- 

 ment of Expan- 

 sion (liquid). 



