250 Apparatus and Processes. 



cylinder, B, with the bore of which it has a corresponding aperture. 

 The brass cylinder is about three inches in diameter, and six inches 

 in height, being inserted at its lower end into a block of wood as a 

 basis. This cylinder receives below, a screw, which supports a cop- 

 per tube, C, of about two inches in diameter, so as to have its axis 

 concentric with that of the cylinder, and to extend about four inches 

 above the plate. The copper tube, thus supported, is closed at the 

 upper termination by a cup of copper, of a shape nearly hemispher- 

 ical, and soldered at the upper edge, to the edge of the tube ; so 

 that the whole of the cavity of the cup, is within that of the tube. 

 Hence the bottom o( the cup is accessible to any body, not larger 

 than the bore of the tube, without any communication arising be- 

 tween the cavity of the tube, and that of any receiver placed upon 

 the plate, over the cup and tube, as in the figure. 



Into the side of the cylinder supporting the plate, a valve cock is 

 screwed, by means of which, and a flexible leaden tube, a communi- 

 cation with an air-pump is opened, or discontinued, at pleasure. 



The cup being first covered with a portion of the vitrified boracic 

 acid, as anhydrous as possible, and finely pulverized, the potassium is 

 introduced, and afterwards covered with a further portion of the 

 same acid, two parts of the potassium being used for one of the acid. 

 A large glass receiver is now to be placed on the plate, secured by 

 rods A, A, concentric with the tube and cup ; from the heat of which 

 the glass is to be protected by a bright cylinder of sheet brass, S, 

 placed around it so as to be concentrical with the receiver and tube. 



The apparatus being so prepared, and the receiver exhausted of air 

 by means of the air pump, an incandescent iron is introduced 

 through the bore of the tube, so as to touch the bottom of the cop- 

 per cup. In a short time a reaction commences, which aiding the 

 influence of the hot iron, renders the cup and its contents red hot. 

 A deep red flame appears throughout the mass, after which the reac- 

 tion lessens, and the heat declines. 



When the cup has become cold, the air is admitted into the receiv- 

 er, and the contents are washed with water. If any of the acid has 

 escaped decomposition, it may be removed by boiling the mass with 

 a solution of potash or soda. After this treatment and due desicca- 

 tion a powder will remain, having the characteristic color and proper- 

 ties of boron. 



