AIR PUMPS AND APPARATUS. 



217 



pressed into half its former bulk ; being pressed by one 

 additional atmosphere. 



Price, of the tube, graduated, with cap 



and stop-cock, - $5.00. 



Water Pump in Vacuo. (Fig. 224, opposite page.) This 

 represents an open top receiver with the common water 

 pump placed on the top ; the tube of the pump being within 

 the receiver, and the end immersed in a vessel of water. 

 On working the piston the water will readily flow ; but ex- 

 haust the air from the receiver, and when a good vacuum is 

 obtained the water cannot be raised by working the pump. 

 This shows that all the phenomena of suction and pumps 

 are not owing to the abhorrence of a vacuum in nature, but 

 to the pressure of the air. Price, $8.00. 



Fig. 223. Freezing Apparatus. Prof. Leslie's 



experiment of freezing water in vacuo, 

 by its own evaporation (Fig. 225) is 

 shown by a shallow glass vessel, as a 

 watch-glass, for containing the water 

 to be frozen, which is supported over 

 a wide glass basin, containing strong sulphuric acid, the 

 whole covered by a low receiver. When the air is exhaust- 

 ed from the receiver, the acid will absorb the vapor from 

 the water as rapidly as it is found, thereby abstracting the 

 sensible heat from the water, till congelation ensues. 

 Price, $1.50 and $2.00. 



Fig. 226. 



Freezing Apparatus with Thermo- 

 meter. (Fig. 226.) The same appa- 

 ratus as the last described, used un- 

 der the receiver with sliding rod, in 

 place of the low receiver, and having 

 a delicate thermometer with exposed 

 bulb dipping into the water, indicating 

 the gradual reduction of temperature 

 during the process. 



Price, $3.00. 



" with slide rod receiver, 



$5.00 and $7.00. 

 " thermometer only, $1.00. 

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