Mr Potter on the Specific Heats of Metals, Sfc. 77 



by the other mode, and also that they did not immediately con- 

 sider the possible effect of their cylinder of silver, and of the 

 bulb of the thermometer necessary to be used. As the matter 

 stands, their table will be found to contain as great a propor- 

 tion of error as any published on the subject. 



In the method of determining the specific heats of solids not 

 acted upon chemically by water, by immersing them in a known 

 weight of that liquid at another temperature, and then noting 

 the resulting temperature, it is clear that we have two ways of 

 performing the experiment, — the one where the solid is hotter 

 than the fluid, and the other the reverse ; and the attendant 

 errors, when we compare the results, are, as might be expect- 

 ed, generally in opposite directions, and may thus be rendered 

 serviceable in pointing out the precautions necessary to be used, 

 and the allowance to be made in deducing the correct deter- 

 minations. 



The great source of error in all experiments of this descrip- 

 tion is the alteration in temperature of the materials during 

 the process of the experiment; for it is necessary that either the 

 fluid or the solid body be at a temperature much above that 

 of the air and surrounding objects. From the capacity of 

 water for equal weights being so much greater than that of the 

 metals, the influence of the alteration in temperature in pro- 

 ducino- error is much greater when the cold metal is immersed 

 in tepid water than in the other way ; and greater dexterity 

 and more precautions are required. 



In some of my first trials I used a vessel of tin-plate to con- 

 tain the water, and obtained the following results : — 



Specific heat deduced Specificheat deduced 



Quantity from immersing the from immersing the 



of the metal at 212° in an metal at 55° in an 



metal used, equalwcightofwuter equalweightof water 



at common temps. at about 103° 



For equal For equal For equal For equal 

 weights. bulks. weights. bulks. 



Hard steel, life. 1U oz .1026 .800 



Speculum 



