of freezing at a distance^ 73 



and the apparatus, though admirably adapted to the purpose 

 for which it is designed, is large and costly. I have therefore 

 thought the little instrument I am about to describe may pos- 

 sess some interest, as affording a readier and more simple 

 mode of exhibiting so amusing and instructive an experi- 

 ment. 



Let a glass tube be taken, having its internal diameter about 

 i of an inch, with a ball at /^ 

 each extremity of about one Q^ 

 inch diameter; and let the ^^ 

 tube be bent to a right angle at the distance of half an inch 

 from each ball. One of these balls should contain a little* 

 water, and the remaining cavity should be as perfect a vacuum 

 as can readily be obtained. The mode of effecting this is well 

 known to those who are accustomed to blow glass. One of 

 the balls is made to terminate in a capillary tube, and when 

 water admitted into the other has been boiled over a lamp for 

 a considerable time, till all the air is expelled, the capillary 

 extremity, through which the steam is still issuing with vio- 

 lence, is held in the flame of the lamp till the force of the 

 vapour is so far reduced, that the heat of the flame has power 

 to seal it hermetically. 



When an instrument of this description has been success- 

 fully exhausted, if the ball that is empty be immersed in a 

 freezing mixture of salt and snow, the water in the other ball, 

 though at the distance of two or three feet, will be frozen 

 solid in the course of a very few minutes. The vapour con- 

 tained in the empty ball is condensed by the common opera- 



• If the ball be more than half full, it will be liable to burst by the expansion of 

 water in freezing. 



MDCCCXIII. L " 



