APPENDIX II. 145 



work, that is, in overcoming the pressure of the 

 atmosphere. In the second case, both the combus- 

 tible and the supporter of combustion are in the 

 solid condition, whilst a considerable proportion of 

 the products of combustion are gases. The genera- 

 tion of the latter cannot take place without the per- 

 formance of external work, for every cubic inch pro- 

 duced must obviously, in overcoming atmospheric 

 pressure, perform an amount of work equivalent, in 

 round numbers, to the lifting of a weight of 15 Ibs. 

 to the height of one inch. In performing this work 

 the gases are cooled, and consequently less heat is 

 communicated to the water of the calorimeter. 

 Nevertheless, the loss of heat due to this cause is 

 but small. Under the actual conditions of the 

 experiments detailed below, its amount would only 

 have increased the temperature of the water in the 

 calorimeter by 0'07 C. Even this slight error is 

 entirely eliminated by the final correction which we 

 have now to consider. 



It is well known that the decomposition of 

 chlorate of potash into chloride of potassium and 

 free oxygen is attended with the evolution of heat. 

 If a few grains of peroxide of manganese, or better, 

 of peroxide of iron, be dropped into an ounce or two 

 of fused chlorate of potash which is slowly disen- 

 gaging oxygen, the evolution of gas immediately 

 proceeds with great violence, and the mixture be- 

 comes visibly red hot, although the external applica- 

 tion of heat be discontinued from the moment when 

 the metallic peroxide is added. The latter remains 

 unaltered at the close of the operation. It is thus 



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