EXPERIMENTS OF DULONG AND PETIT. 81 



2. It has been found by geologists, that where 

 beds of bituminous coal have been perforated by 

 mineral veins, (which were originally the con- 

 duit pipes for the escape of volcanic heat,) it has 

 been changed into coke, or nearly pure carbon. 



3. That beds of anthracite are confined chiefly 

 to mountainous regions; whereas inflammable 

 coal belonging to the same geological epoch, is 

 found in vast quantities between horizontal strata 

 of sandstone and shale. But I must return from 

 this digression to the immediate subject of in- 

 quiry. 



After all attempts to ascertain the specific heat 

 of bodies had proved discordant and fallacious, 

 a series of experiments was undertaken by MM. 

 Dulong and Petit, the object of which was to 

 discover what relation existed between the atomic 

 weights of various bodies and their capacities for 

 caloric. The result of their researches was, that 

 the specific heat of water was nearly three times 

 that of sulphur and several of the metals, in which 

 it was about one half less than in some other 

 elements, four times less than in others again, such 

 as phosphorus and iodine, while in carbon it was 

 nearly six times less than in water, or as 0*169 

 to I'OOO. They also found that there was no 

 uniform relation between the quantities of caloric 

 evolved during the combustion of different bodies, 

 and the specific heat of their resulting products, 

 the capacity of which was often the same before 

 as after the process. Yet they maintained that 



G 



