218 BENJ. PIKE'S, JR., DESCRIPTIVE CATALOGUE. 



Fig. 223. 



Wollastons Chryophorus in Vacuo. The cliryophorus 

 in this arrangement (Fig. 227, as above) has a circular piece 

 of brass, truly ground on the under side, and fitting the 

 open top receiver, and also having in the centre a block of 

 wood, well varnished, to render air-tight and surrounding 

 the tube of the chryophorous ; by this contrivance one of 

 the balls may be introduced within the receiver, and a va- 

 cuum obtained. 



To use : cover the interior ball with a sponge, or cotton, 

 which may be tied on, and wet it well with ether ; turn all 

 the water in the upper ball. On exhausting the receiver, the 

 vapor in the interior ball of the chryophorus will be con- 

 densed by the evaporation of the ether, which will produce 

 evaporation from the surface of the water in the upper ball, 

 which vapor continues to condense, producing continual 

 evaporation from the surface of the water in the upper ball, 

 till the water therein is frozen. To prevent injury to the 

 pump from ether entering therein, a cup is placed on the 

 plate to receive any drops from the sponge. 



Price, $5.00. 



The Flint and Steel in Vacuo. In the best construction 

 of this instrument (Fig. 228) a gun lock is supported in a 

 brass frame, and attached by a pillar to the centre of the 

 pump plate ; the lock has a brass arm terminated in a small 

 cup at one end, and at the other fixed to the lever of the 



