338 



Mr. J. Dewar on the Physical 



bath (C), and the palladium dropped in. This arrangement of 

 the calorimeter is very convenient in a small chemical labora- 



tory, where uniformity of temperature cannot be easily com- 

 manded. The constancy of the radiation in the calorimeter 

 makes the correction for cooling very exact. 



The same arrangement of the calorimeter is employed for re- 

 gistering very small amounts of heat by placing in A bisulphide 

 of carbon or chloroform, packing the middle and outer compart- 

 ments of the tin vessel full of pounded ice, and covering the 

 exposed surface with sawdust. The thermometer is now pro- 

 vided with a thin sheet-copper stirrer, instead of the india-rubber 

 one formerly used. The rate of cooling is in this case deter- 

 mined once for all for a range of 5° above zero, and plotted in 

 a curve. Erom this curve the correction for the radiation is de- 

 termined for all subsequent experiments. 



Two series of experiments were made. In the first series bar, 

 and in the second plate palladium was used, three different hy- 

 drides* of each. The experimental results are given in Tables 

 II. and III. 



In the case of the bar the specific heat of the occluded hy- 

 drogen increased as the charge diminished, the extreme values 

 being 3*79 and 5*05. Similarly with the plate the values are 

 greater, and have a wider range, viz. from 3*93 to 5*88. These 

 results are calculated in each case for the heat given to the 



* In this paper the term hydride is not used in its strict chemical sense, 

 but as a convenient abbreviation. 



