J88 ^^W MERCURIAL AlH-WMT, 



broken to pieces to put into the lime kiln, and quite clean, 

 nearly of a fjze, and alraolt without any chalk powder mixed 

 with them. 



I remain, &c. 

 Sorcthampton, Jan, 22, 1 800. 



V. 



Defer iption of a mercurial Air-pump, of unlimited exhavjiing 

 Poiver, with a Wooden Pijton, working in a Wooden Cylinder, 

 ^ Sfc, By Sir A, N. Edelcrantz, 4^* ^c. Communicated 



by the Author, 



ConftruAion of aIaVING refided a long time in a place, where no ma* 



•n air pump in thematical inftrument maker could be had, I was obliged to 



4ualfpace is left, contrive fome method of conftruding an air-pump, in which 



common workmen and common materials could be er^ployed, 



Beiides which, as in almoft all former conftrudions of this in-. 



iirument, a fmall fpace exifls in fome part of them, where the 



air remains condenfed, &nd confequently a limit is fixed to the 



expanfion, I was defirous, if poffible, to remove this feemingly 



material, though in good pumps infinitely fmall defed. Thefe 



confiderations led me many years ago to a contrivance, of which 



the following fliort defcription may give a notion, referving a, 



more detailed one, with a more particular account of its effeds, 



to a future publication. 



Defcription with A B C D, Plate XII. is a folid piflon of wood, cylindrical or 



a drawing. fquare, * moving up and down in a fimilar wooden box or tube. 



It operates by ^ * » * ' 



mercury raifed E F G H, by means of rack-work at H. The pifton fills the 

 and lowered m a ^^^ j„ j^g whole length as exadly as poffible, without touching 



wooden pipe, by . -.-^. -oi^i -r. i r i 



a plug, and the and producmg friction agamit the tides. i*or that purpole the 

 upper communi- pjfton is guided at the lower end by an iron rod KI, fixed in 

 receiver is made ^^^^ bottoiTi of the box and entering the pifron, and at its upper 



through ati iron part by a roller, which runs along the inner furface of the bar- 



*^°^ * rel. The cavity of the wooden box extends through the canal 



F Mf to the iron cock O, and communicates at M with a per- 



* I have, m the execution, preferred the fquare form, as raor« 

 eafy to make exaft and equal in its whole length* 



f All the wooden parts are made of ftrong oak, and are covered 

 with a good refinous yanViQi, to prevent the ahforption of mercury: 



pepdicular 



