and on the Isomeric Modifications of Selenium. 491 



undergone by the calorimeter, on account of perturbations pro- 

 duced by external causes. This modification exercises, however, 

 little influence on the results. 



The method of proceeding was as follows : — 



1. The variation of temperature A^, which the calorimeter 

 underwent from disturbing causes alone, was observed during 

 three minutes, the water being continually agitated by means of 

 a small stirrer which formed part of the apparatus. 



2. The calorimeter was placed rapidly under the oven, in 

 which the little basket containing the substance experimented 

 upon had been raised to a temperature accurately determined, 

 and about 100 degrees. The basket was then quickly lowered 

 into the water of the calorimeter, and this was then returned 

 to its original position in front of the telescope which served for 

 reading the thermometer. It took half a minute to place the 

 calorimeter beneath the oven, and to make the necessary ar- 

 rangements for lowering the basket ; during this time the calo- 

 rimeter underwent a variation of temperature similar to that 

 which had occurred in the same time during the first period. 

 The lowering of the basket only required a few seconds ; and as 

 this basket was immediately agitated, the water assumed in less 

 than a minute its maximum temperature when the substance 

 was a good conductor of heat. At the end of the fourth minute 

 the calorimeter was brought to its first position, and its tempe- 

 rature might be read off^. 



3. From minute to minute the temperatures of the calorimeter 

 and of the surrounding medium were observed till the seventh 

 minute. 



4. Lastly, an observation was made of the variation of tempe- 

 rature which the calorimeter underwent from disturbing causes 

 alone during the three succeeding minutes, that is, from the 

 seventh to. the tenth. 



Representing by — • 

 A, the value in water of the calorimeter with its appendages, 



that is, the immersed part of the thermometer and the little 



agitator j 

 M, the weight of the substance submitted to experiment ; 

 p, the value in water of the basket ; 

 T, the temperature indicated by the thermometer of the oven, 



corrected for that portion of the column which is outside ; 

 ^', the temperature of the calorimeter at the end of the seventh 



minute ; 

 A^, the elevation of temperature observed between the end of 



the third minute and that of the seventh ; 

 A^', the elevation which it would have undergone if it had not 



been influenced by disturbing causes ; 

 2K2 



