OF ARTS AND SCIENCES. 



71 



contrived by him for excluding the action of atmospheric air 

 during the process of filtration. By means of it, this process 

 may be conducted either in a confined portion of air, in 

 vacuo, or in any gas. 



" It is frequently important in chemical analysis to conduct the pro- 

 cess of filtration either in vacuo or in a neutral gas, and especially 

 in an atmosphere free from carbonic acid. In order to overcome 

 certain difficulties, I have been led to contrive an apparatus for this 

 purpose, which I believe to be superior to all others now in use, both 

 on account of its simplicity and its cheapness. The complete appa- 

 ratus is represented in Fig. 1, and some of its parts enlarged appear 

 in Fig. 2. It consists of a wide-mouthed glass bottle, into the neck of 



which is ground with emory a funnel (a. Fig. 2), having a short but 

 large spout. This funnel is made sufficiently thick to resist the at- 

 mospheric pressure, and its rim is ground so that it may be closed 

 air-tight by a glass plate, or by a brass plate, connecting with an air- 

 pump. Within this outer funnel the common filtering-funnel is 

 placed, resting loosely against its side so as to allow a free passage of 

 air. In order to wash the precipitate, a glass plate having a hole an 

 inch and a half in diameter drilled through its centre {d, Fig. 2) is 

 substituted for the covering-plate. Through this passes the tube of the 

 washing-bottle (/, Fig. 2). The washing-bottle is made in the ordi- 

 nary way, except that it is fitted with a cork, which projects about an 



