344 ^'1^ Efcapement.-^Furnace for Fvjiin, 



experiment proved in favour of the crank; though with the common efcapemcnt, well ad' 

 jufted, I kept the pendulum in motion for fome days, with as fmall a power as I could 

 with ihe crank ; yet the fame fma]! power with the commoa efcapement was not fufficient 

 to maintain the motion fojong as it was with this crank. The weight here ufed for this 

 eight-day piece, whieh has kept it going for about fix months without once failing, is 451b* 

 It has in it an allowance of more than half for the lofs of power from foulnefe, or other ac- 

 cidents ; for three pound was fufficient to work, the clock for feveral weeks when firft put. 

 together. 



IV. 

 Defcript'ion of the Furnace of PoTT^ 



Ta Mr. Nicholson. 



M, 



Sir, 



-UCH has been faid on the theory and conftru£tion of chemical furnaces, and many in- 

 genious contrivances have been made on that head, efpecially for philofophlcal purpofes and' 

 experiments in the fmall way ; yet, to my knowledge, there is none by which in fo fimple a 

 manner, and moderately fmall fize, the heat caa be increafed to fuch intenfity as by Pott's 

 furnace. — I mean Pott the famous Pruffian chemift, which, though his refearches on the- 

 more fimple earths and ftones were chiefly confined to their degree of fufibility, or alfo of 

 their being fire-proof, may neverthelefs be confidered as the father and forerunner of thofe 

 admirable analyfes of mineral fubftances, for which the prefcnt period is indebted, after 

 Margraf and Gellert, to Gerhardy Jchard, D'Jrcet, and efpecially to Klaproth and 

 Vaitqueltn. 



That furnace, it feems, has been long fince forgotten ; and perh«ps it may be of fervice to 

 the chemical public to be again put in mind of it. Qn this account I fend a drawing, and 

 tranflation of the defcription, which Pott himfclf publirtied of his furnace. If you are of the 

 fame opinion, and think it may be agreeable to the readers of your valuable and ufeful 

 Journal, you are requefted to- infert it. 



Sir, your humble obedient fervant, 

 i^tk Offdier, 1799» N. N. 



yfy Account of Pottos Furnace, given by himfelf. 



When I affirmed in my treatife on the Lithogeogmfif*, that the culinary and common 



* John Henry Pott's Lilbogtognofia, or chemical enquiries into the nature of the common more fimple 

 ftones and earths, etc. 4to. Berlin, 1784, Continuat. id. By the Ihape of this furnace, it appears that its 

 iniidc, after being coated, has the form of the cavity of an egg, or nearly elliptical, which was thc.favourite 

 flkape with JJo/ri'Aai'r, for furnaces intended to produce a ftcong heat. 



fires 



