[ 8G1 ] 



XXVII. On the Expansion by Heat of Metals and Alloys. By A. MATTiuESSEy, F.B.S. 



Received June 20,— Head June 21, 1866. 



Is a memoir "On the Expansion by Heat of Water and Mercury"*, I described a 

 method of determining the expansion of bodies by weighing them in water at different 

 temperatures. This method was chosen on account of its yielding accurate results with 

 comparatively small quantities, for to purify large quantities of metal would entail 

 immense labour and expense ; so much so, in fact, that to purify sufficient quantities to 

 make bars for the determination of the linear expansion would be practically impossible. 

 On determining the expansion of the metals by this method, I found that they did 

 not expand regularly between 0° and 100°. The difference, however, between the rates 

 of expansion between 0° and 50° and 50° and 100° was found to be so gi-eat that part of 

 it might be possibly attributed to errors in the determination of the coefficients of expan- 

 sion of water, as the coefficients of expansion of the metals are comparatively small 

 when compared with those of water. Now, although the coefficient of expansion of mer- 

 cury when determined by this method agrees with Eegnault's value, yet on account of 

 this value being large, small errors in the water coefficients will not materially influence 

 it ; for the volume of water at 



4°=l-0000, at 100°=1-04316, 

 that of mercury at 



0°=1-0000, at 100°=1-01815, 



and that of copper, for instance, at 



0°=l-00000, at 100°=1004998, 



showing that the expansion of copper is very small compared with that of water or 

 mercury. 



This fact led me to make another series of check experiments by determining the 

 linear expansion of a certain copper bar, as described in the first part of my paper abo^e 

 quoted, and then weighing a piece of it, turned to the shape of a double cone, in water 

 at different temperatures. 



The following are the results obtained with the copper bar ; and it may here be men- 

 tioned that copper does not behave in one respect like glass. The glass rods, as there 

 shown, do not return directly to their original length after being heated to 100° and 

 cooled rapidly ; copper, however, does so ; for no differences in the coefficients were 

 observed after heating the rod to 100°, determining its expansion, alloMing it to stand 

 over night, and redetermining the coefficients. 



* Philosophical Transactions, 1866, Part I. 



MDCCCLXri. 6 A 



