EXPANSION 



319 



If the density of water at 39 be called 1 '00000, 



at 212 iC becomes . . . . . 0-9548, 

 and its volume has increased to . . 1-04734 ; 

 at 77 it becomes . . ' * . ' . 9973587, 

 and its volume has increased to only . 1 '00265, 



which, though one-fourth of the whole range of temperature, is only ^ of the total 

 expansion. Water at 60 F. has a specific gravity of . 0-9991253, 



and has increased in volume from 39 to . 1 "00008, 



which is only about i of the total expansion to 212, with g ? 5 of the total range of 

 temperature. 



All gases expand the same quantity by the same increase of temperature, which 

 from 32 to 212 F. =ifg = | of its initial volume, or 100 volumes become 1-375. For 

 each degree of F. the expansion is ~. 



When dry air is saturated with moisture, its bulk increases, and its specific gravity 

 diminishes, because aqueous vapour is less dense than air, at like temperatures. 



The following Table gives the multipliers to be employed for converting one volume 

 of moist gas at the several temperatures, into a volume of dry gas : 





Lavoisier and Laplace arrived, after an extensive series of experiments, at the two 

 important conclusions following : 



1st. All solid bodies -whatever, being gradually heated from the temperature of 

 melting ice to that of boiling water, and then gradually cooled from the temperature 

 of boiling water to that of melting ice, will be found to have exactly the same dimen- 

 sions at the same temperature during the process of heating and cooling ; the gradual 

 diminution of bulk in cooling corresponding exactly with the gradual increase of bulk 

 in heating. 



2nd. G-lass and metallic bodies gradually heated from the temperature of melting 

 ice to that of boiling water, undergo degrees of expansion proportional to those of 

 mercury at the same temperature ; that is to say, between the limits just mentioned, 

 the expansion of the solid corresponding to two degrees of the thermometer, is twice 

 the expansion which corresponds to one degree, the expansion which corresponds to 

 three degrees is three times the expansion which corresponds to one degree, and so 

 on ; the quantity of expansion being multiplied in the same proportion as the number 

 of degrees through which the thermometer has risen is multiplied. See HEAT, 

 Watts 's ' Dictionary of Chemistry.' 



Experiments by Fresnel, Forbes, Powell, Trevelyan, and Tyndall have a tendency 

 to prove that heat occasions a repulsion between the particles of matter at small dis- 

 tances. If a heated poker is laid slantingly on a block of lead at the ordinary tem- 

 perature, it will commence to vibrate, first slowly, and will increase with such rapidity 

 as to produce a musical note, which continues for some time, usually changing to an 

 octave at the termination. These results would appear to prove a movement amongst 

 the particles constituting the bar. 



Some remarkable examples of expansion are furnished by the influence of sunshine 

 on the Britannia Tubular Bridge. 



The most interesting effect is that produced by the sun shining on one side of the 

 tube, or on the top, while the opposite side and bottom remain shaded and compara- 

 tively cool ; the heated portions of the tube expand, and thereby warp or bend the tube 

 towards the heated side, the motion being sometimes as much as 2^ inches vertically 

 and 2 inches laterally. 



While the tubes were supported on the temporary piers on the beach, these motions 

 were easily observed. An arm carrying a pencil was fixed on the south side of the 



