122 Prof. Regnault on the Specific Heat of some Simple Bodies. 



Several experiments made in this way have given very discord- 

 ant results. The reason is, that at a low temperature boron 

 absorbs and condenses a large quantity of air, which it disen- 

 gages often with a brisk effervescence the moment the basket is 

 immersed in the calorimeter. To avoid this source of error it 

 would have been necessary to press the amorphous boron in a 

 brass cylinder, which was then hermetically closed. I tried in 

 fact to make the experiment in this way ; but boron in this pure 

 state of division is such a bad conductor of heat, that the water 

 of the calorimeter only assumes its maximum temperature after 

 a lengthened immersion; and that renders the determination very 

 uncertain. 



I then decided to heat the boron in the water- bath. The 

 pulverulent boron was strongly pressed in a very thin brass 

 cylinder, which was closed with a circular leaden cover to pro- 

 tect the substance completely from the action of the air. The 

 brass vessel was suspended in the bath of fig. 1, the reservoir of 

 the thermometer occupying the central space of the vessel. I 

 soon found that the thermometer rose much more rapidly than 

 when the vessel contained another substance ; after some time 

 it even exceeded the temperature of 100°. I thought at first that 

 this arose from the boron undergoing at this temperature one of 

 those allotropic modifications which M. Deville has mentioned; 

 but I have since found that this increase of temperature simply 

 arises from a brisk absorption of oxygen by the boron, which 

 takes place at about 100°, and changes it into boracic acid. This is 

 soon seen by digesting in the water of the calorimeter the boron 

 which filled the basket. This water, filtered, gave on evaporation 

 a notable quantity of boracic acid, which certainly arose from an 

 oxidation which the boron had experienced in the bath, spite of 

 the precautions which had been taken to isolate the surrounding 

 air; for the boron had been repeatedly washed with distilled 

 water, and then dried in vacuo over sulphuric acid before being 

 compressed in the circular vessel. 



This second method of experimenting presents therefore an 

 important source of error, and confidence cannot be placed in its 

 results. I nevertheless transcribe the elements of the three 

 experiments made in this manner : — 





I. 



II. 



III. 



M . . 



20^-14 



19^22 



18& r -88 



P • • 



1^-1451 



1«"1451 



lg r 1451 



T . . 



104°-1Q 



99°-70 



101°-55 



& . . 



. 10°-41 



14°-19 



15°- 14 



A0' . . 



2°-0771 



l°-5934 



1°-6315 



A . . 



422^30 



422? r -30 



422^30 



