HEAT OR CALORIC. 



2. Glass so heated by the friction of a cord, as to separate into 

 two parts, on being subjected to cold water. 



" Some years ago, Mr. Lukens showed me, that a small phial 

 tube, might be separated into two parts, if subjected to cold water, 

 after being heated by the friction of a cord made to circulate about 

 it by two persons alternately pulling in opposite directions. I was 

 subsequently enabled to employ this process, in dividing large ves- 

 sels, of four or five inches in diameter, and likewise to render it, in 

 every case more easy, and certain, by means of a piece of plank 

 forked like a boot jack as represented in the preceding figure 

 and also having a kerf, or slit, cut by a saw, parallel to, and nearly 

 equi-distant from, the principal surfaces of the plank, and at right 

 angles to the other incisions." 



" By means of the fork, the glass is easily held steady by the hand 

 of one operator. By means of the kerf, the string, while circulating 

 about the glass, is confined to the part, where the separation is de- 

 sired. As soon as the cord smokes, the glass is plunged into water, 

 or if too large to be easily immersed, the water must be thrown upon 

 it, This method is always preferable when the glass vessel is so open, 

 that on being immersed, the water can reach the inner surface. As 

 plunging is the most effectual method of employing the water, in the 

 case of a tube, I usually close the end which is to be sunk in the wa- 

 ter, so as to restrict the cooling to the outside." 



10 



iter, 



