536 
MR. T. J. BAKER ON THE THERMO-CHEMISTRY 
the calorimeter at the instant the mercury passed the upper mark, and Avithdrawing 
it at the instant it passed the lower. 
It was found to evolve 457'4 calories. 
A similar experiment was now performed with the sidjstitution of 550 grammes of 
the solution for water, and the specific heat was calculated. 
The results of three determinations were :— 
(i.) ‘752 (ii.) '755 (iii.) '755. 
The mean of these values is ‘754. 
The water equivalent of the calorimeter and all its contents was therefore 
(550 X ’754)+ 16 = 430'7 grammes. 
Correction for Radiation. 
Since the excess of temperature of the calorimeter above its surroundings at the 
end of an experiment was usually about 1° C. only, the correction necessary for 
radiation during the short period occupied l^y the dissolution of the metal was alwavs 
very small. 
The temperature was read every half minute from the beginning of an experiment. 
The maximum was usually reached after one and a-half or two minutes had elapsed, 
the greater part of the rise in temperature occurring during the first half minute. 
The readings were then continued for several minutes, as the temperature slowly 
fell, and the rate of cooling per half minute was found. 
It was assumed that during the first half minute of the rise in temperature there 
would be no sensible radiation loss, as a certain interval of time would elapse before 
the exterior of the calorimeter attained the temperature of its contents. 
The radiation correction was therefore calculated by multiplying the rate of 
cooling by the number of half minutes, less one, occupied by the rise in temperature. 
This correction was usually less than ’5 per cent, of the observed rise in 
temperature. 
Heat of Dissolution of Copper in Ammonium Ferric Chloride Solution. 
The copper was prepared exactly as for the experiments with chlorine water, and 
was introduced into the calorimeter on a paraffined-paper tray after it had been 
moistened with a very little water. 
