266 Wadsworth — Determination of Specific 



stant temperature will, I think, be found especially reliable 

 and convenient. 



In the method of mixtures the body whose specific heat is 

 to be determined is first raised to a known temperature, then 

 immersed in a known quantity of water and the rise of temper- 

 ature of the water noted. In the operation it is of course 

 necessary that the water be held in some form of vessel which 

 will be heated in common with the water, and which in turn 

 will heat the surrounding air by radiation. However, taking 

 first the theoretical case and supposing no heat lost by radia- 

 tion, but all used in raising the temperature of the water, the 

 containing vessel and the thermometer used to indicate the 

 rise in temperature, we have the well-known equation 



sx{T-0)xw=zMc{0-t)+M'c'{e-t)+M"c"($-t) (1) 

 where s _ _ is the specific heat of the body under experiment ; 

 io.. " weight " " " 



T-. " temperature " " before immersion ; 



M__ " weight of water in the calorimeter; 

 c . _ " mean specific heat of the water for the interval 



0-t; 

 t _. " temperature of the water before the body w is 



added ; 

 .. " temperature of water, vessel and body after 

 equalization has taken place ; 

 M', c' .. are the weight and specific heat of the vessel contain- 

 ing the water, i. e., the calorimeter; 

 M", c" ' .. " weight and specific heat of the thermometer. 



This formula is generally simplified by putting m'c' -\-Wc" = 

 Wc, where W is the water equivalent of the calorimeter, viz : 

 the amount of water which for a given rise in temperature, 

 6 — t, will absorb the same amount of heat as the calorimeter 

 and the thermometer will absorb. 



Making this substitution and solving for s we get 

 (M + W)c(0-t) 

 "--—^jJT^O) ' [Z) 



Xow in practice the quantities M, W, w, 0, t and T, must all 

 be observed (<?, we have determined for us with great accuracy); 

 it is therefore necessary to consider the causes and the magni- 

 tude of the error involved in each of said operations. 



Firsts w. This can be observed with great accuracy because 

 it is generally so small that it can be determined on a delicate 

 balance. It is moreover practically a constant for most bodies, 

 viz : (unaffected by oxidation, heat, etc.), so that no correction 

 is necessary.* 



* A mean of two weighings, one taken before, the other after the determina- 

 tion, should be used to avoid any error due to loss by oxidation, etc. Volatile 

 liquids or substances otherwise affected by heat and contact with hot air are, of 

 course, placed in suitable bulbs of metal or glass for the determination. 



