and on the Isomei'ic Modifications of Selenium. 509 



mean specific heat by the atomic weight is 37*39. This product 

 is comprised within the limits which we have found for other 

 simple bodies. 



To determine the specific heat of vitreous selenium, I could 

 not use the ordinary apparatus, because the substance undergoes 

 its isomeric transformation at 93 degrees. I used the apparatus 

 represented by fig. 2, the trough being filled with hot water. 

 The water of this trough was kept stationary by means of a gas 

 lamp j it was constantly agitated by means of the palette agi- 

 tator m up q. 



Selenium recently melted was cast in the small brass vessel, 

 fig. 1 j this vessel was placed in the middle of the tube AB, 

 where it was maintained by the help of two silk threads attached 

 to the upper and lower base of the vessel, in order to move it 

 readily in lowering the thermometer. 



Weight of selenium . ISSs'-S 185k^-6 



Weight of brass vessel . 81^-2 S\^'2 



T 87°-285 77°'338 



& 19°-49 17°-93 



M 4°-4333 3°-7614 



A 422°-54 422°-54 



c 0*1036 0-1026 



Mean .... 0*1031. 

 The specific heat which we have thus found for vitreous sele- 

 nium is much greater than that which we have obtained for 

 metallic selenium, which only amounts to 0*07616. But this 

 may arise from the fact that vitreous selenium is much more 

 easily softened by heat than metallic selenium, and that at the 

 temperature of 80 or 90 degrees it already contains a consider- 

 able part of its latent heat of fusion. 



In order to decide if selenium possesses different specific heats 

 in its two isomeric states, it was necessary to determine them at 

 very low temperatures, at which neither of the two varieties of sele- 

 nium undergoes a perceptible softening during the period of the 

 temperature to which they are subjected. The selenium was 

 previously melted in the ordinary mould ; it was then in the form 

 of a large cylinder, having in the direction of its axis an aperture 

 in which was placed the bulb of the mercurial thermometer em- 

 ployed to indicate the temperature. The cylinder attached to its 

 two silk threads was kept in the middle of the tube A B, fig. 2 ; 

 and the vessel C D E F was filled with a cooling mixture formed 

 of ice and crystallized chloride of calcium, which was continually 

 agitated. The cooling of the thermometer was followed till it 

 reached its minimum, at which it usually remained ten minutes. 

 At this moment the calorimetric experiment was made. The 

 following are the results obtained with vitreous selenium and with 

 metallic selenium : — 



