CHAPTER III. 

 EXPANSION OF LIQUIDS, 



Volume Expansion of Liquids U-Tube Method applied to Mercury Dulong and 

 Petit Kegnault Expansion of other Liquids by Specific Gravity Bottle By 

 Dilatometer Matthiessen's Hydrostatic Method The Expansion of Water 

 Hope's Apparatus Apparatus of Joule and Playfair Results. 



Volume Expansion Of Liquid. Since liquids have no definite 

 shape of their own, their dimensions depend on the containing vossel. 

 We are, therefore, only concerned with their volume expansion as the 

 temperature rises. 



The most obvious mode of observing the expansion of a liquid is to 

 enclose it in a vessel such as a thermometer bulb, and to note the chango 

 in level of the liquid in the stem as the temperature rises. If we know 

 the expansion of the bulb and stem we can deduce the expansion of the 

 liquid. For suppose, at a given temperature, the liquid reaches to a 

 certain mark on the stem. On raising the temperature the internal 

 capacity of bulb and stem increases, but in general the volume of the 

 liquid increases still more, so that it not only occupies the increased 

 space in the vessel, but also rises in the stem. Its total increase of 

 volume is therefore : increase of volume of bulb and stem to first level 

 + additional volume of stem between first and second levels, and when 

 we know these we can determine the increase in volume of the liquid. 



The linear expansion of the bulb and stem may be measured directly, 

 and the volume expansion is approximately three times as great. Chappuis 

 (Travaux et Mdmoires du Bureau International, 1907) has used this method 

 with a weight thermometer to determine the expansion of mercury. But 

 it is not satisfactory, as we cannot assume that the expansion of the bulb is 

 the same in all directions. Practically there is only one method of accu- 

 rately gauging the internal volume of a vessel, and this consists in finding 

 the weight of a liquid of known specific gravity filling it. Thus, if o> be the 

 weight filling it at one temperature and p is the specific gravity of the gaug- 

 ing liquid used, w/p is the volume. If at a higher temperature the weight is 

 <i>' and the specific gravity of the gauging liquid is />', the volume is u'/p'. 

 So that <j)/p has expanded to w'//o'. The problem of determining liquid 

 expansion in general, therefore, resolves itself into that of determining 

 the specific gravity of some one gauging liquid through the range of 

 temperature over which the expansion is required. This specific gravity 

 must be determined independently of the containing vessel. 



U-Tube Method. The best method yet devised for this purpose is 

 a special application of the U-tube hydrometer. As a simple illustration, 

 let us suppose that two glass tubes are fixed vertically with their upper 

 ends open and their lower ends joined by narrow horizontal tubing. A 

 short length of indiarubber tubing, having a pinch-cock upon it (Fig. 21), 

 is inserted in the horizontal tube. 



