<2Q<2 IMPROVED AIR PUMP. 



Dcfcription of for an experimental philofopher to clean an inftrument which, 



Mendeiffohn's being thus complicated, is not only rendered intricate, but is 



improved air- r J 



pump. a 'f° difficult to be put together again. Being defirous, there- 



fore, to amplify this inftrument, I adopted the conftru6tion 

 here defcribed, by which it is capable of being put together 

 in lefs than half an hour when cleaned, and requires that 

 operation very feldom. 



I fubmit to the judgment of your fcientific readers how far the 

 prefent inltrument anfwers its dell red purpofe. I have rejected 

 that tube which, in common air-pumps, leads from the valves 

 to the receiver, together with the cock that ierves to fhut this 

 pipe: the 'receiver is placed immediately upon the valves, 

 thefe being put on the top of the cylinders, which, confe- 

 quently, required the rackwork and pinion to be underneath, 

 and inverted the whole inftrument. See the adjoining draw- 

 ing, Plate VI. where A B and C D reprefent the two cy- 

 linders of glafs ground and polithed infide. E and F are the 

 two valves that allow the cylinders to communicate with the 

 receiver O through two very fliort canals AB and C D (Fig 2, 

 Plate VII) and the cock G. Two other valves that open into 

 the atmofphere are within the covers i and k, as may be feen in 

 Fig. 1, where e repreients one of them. M N is the receiver- 

 plate of glafs ground flat ; P Q a barometer-gauge, upon 

 the plan of the firft Torricellian tube, as the eafieft to conftrucl 

 and the mod infallible in its effects. It will be found to be 

 here quite out of the way„fecure from being broke by accident, 

 and the mod in fight. H K and I L are two brafs pillars that 

 fupport the whole. R S V W the ufual rackwork, having a 

 double winch I in, which, upon trial, will be found preferable to 

 a fingle one. 



It will now be neceffary to fiiew how this pump acts, in 

 which it will be fufficient to explain the aftion of one cylinder, 

 becaufe the other is in all parts alike. E is a conical metallic 

 valve, from which a canal goes through the cock G up to the 

 receiver, as is feen in Fig. 1 and 2, Plate VII. where all the 

 parts are marked with the fame letters. E T is a fteel rod 

 going through a leather box in the pifton U. The top of this 

 rod is fixed to the valve E, and its bottom part Hides in a 

 fmall hole with an allowance of 0,1 inch up and downward, 

 consequently the valve E can move no farther. When the 

 pifton defcends, it firft opens the valve by puthing the rod to 



the 





