608 M. Regnault on the Specific Heat of Simple Bodies, 



a metallic polish. In short, selenium exhibits, in this modifica- 

 tion, the metallic character as decidedly as tellurium. 



Vitreous selenium may be maintained many hours at a tempera- 

 ture of 90 degrees without undergoing the isomeric modification. 



Metallic selenium is a better conductor of heat than vitreous 

 selenium. This fact is easy of demonstration when the specific 

 heat is determined ; with vitreous selenium, the time required 

 before the thermometer of the calorimeter attains its maximum 

 temperature is two or three times as long as with metallic selenium. 



Some selenium, melted at a temperature of 300 degrees, was 

 thrown into very cold water ; it solidified in large intertwined 

 threads, having a very hard and vitreous fracture. The substance 

 exhibited the same aspect as when allowed to cool in the air after 

 fusion. 



Vitreous selenium does not lose its characteristic properties by 

 being pulverized. I placed selenium, recently powdered, in a 

 glass tube, in the axis of which was a mercurial thermometer, 

 and arranged the tube in the oven for specific heats kept at a 

 temperature of 100 degrees. When the thermometer had reached 

 97 degrees, it mounted suddenly and with great rapidity until it 

 reached 160 degrees. The substance had changed its aspect : it 

 had agglomerated, and had assumed the metallic appearance. 



Selenium, precipitated in the state of red powder from its 

 solutions, belongs to the vitreous modification. To assure my- 

 self of this, I dissolved 50 grms. of selenium in nitric acid ; then 

 after having evaporated it to dryness and redissolved it in water, 

 I precipitated the selenium by a current of sulphurous acid. The 

 precipitate, quickly washed with water, was dried in vacuo. The 

 pulverulent selenium was heaped up in a glass tube round the 

 bulb of the thermometer, and the tube placed in the oven heated 

 to 100 degrees. At about 94 degrees the thermometer assumed 

 a very rapid upward march till it reached 150 degrees. The sub- 

 stance was aggregated together in several metallic gray masses, 

 and had separated from the thermometer. In consequence of 

 the latter circumstance, the thermometer had not reached a 

 higher point. 



The following are the experiments which I made on the spe- 

 cific heat of metallic selenium : — 



Mean .... 0-07616. 

 The atomic weight of selenium is 49 J . The product of the 



