EXHAUSTING MACHINE. ^5 



cover I on it. On openin;r M, the mercury will descend 

 bj' the tnbe, and leave the i-eceiver exhausted. By shutting 

 the cock N, the vacuum is rendered more secure. 



A small degree of contrivance will adapt this apparatus Contrivances 

 to every experiment, which can be performed with the com- ^Iff^^'^l^^j '* ^°. 

 mon air pnrap. If we wish to experiment on fluids, they r m-nts, as oa 

 may be enclosed in a fiask of the form of fijy. 3. The screw ^ ' 

 at its bottom must be perforated so as to permit the descent 

 of the mercury when it is iixed in G. A ground stopper of 

 glass, e, is to be placed in the neck of the flask, c, after it is 

 filled with the liquid to be subjected to experiment : the flask 

 is to be screwed to the plate A, and when the receiver is 

 exhausted, the stopper is to be witlidrawn by the sliding 

 wire, fig. 4, which with its ground plate is to be substituted 

 for I. The length of the stopper of the flask will afford 

 room for the expansion of the liquid. 



When we wish to exhibit the pressure of the atmosphere Pressure of the 

 by means of the apparatus, ^g.5, till both jars, and exhaust atmosphere 

 them ; force down the flat button, which is screwed on the end 

 of the sliding wire, till it covers the orifice of the small jar, 

 and then let the atmospheric air into the outer receiver, by 

 the cock K. The small receiver will adhere to the plate. 



By similar slight changes in the other usual apparatus of 

 an air pump, they may be adapted to the exhausting ma- 

 chine. 



The advantages of an apparatus, such as I have now de- Advantages of 



scribed, over the air-pump, seem to me of considerable ^^'^ ^.P'^^.'"^'"* 



descrioeu, 

 consequence. 



1. The vacuum will be much more perfect; being only 

 aflfected by the small quantity of air adhering to the mer- 

 cux'y, or by the conversion of the mercury into vapour, 

 which is as much as possible obviated by the cock N, 



2. There will be a great saving of manual labour. 



3. Exhaustion will be more quickly performed than by 

 the common pump. 



4. It is more simple than the pump, and less liable to be 

 deranged. 



5. The expense of this machine will not exceed, I a:ppre- Not expensive. 

 hend, that of one of the best air pumps, while it exhausts 



more perfectly. Where nice chemical experiments are con- 

 VoL. XXI— -Sept. 1808. F ducted. 



