Portable Poivder-prsof. 199 



mined, bccaufe it expreffcs the weight which ferved for its graduation, and. the inftrument 

 may liicewife be ufefully applied far weighing fuch bodies as fall within the limits of its fcale. 



The little attention I paid to render this inftrument public, and the prejudice which, in 

 moft cafes, gives a preference to things brought from foreign countries, have caufed it to be 

 defignated as the Englifli or German powder-proof; but the fail is, that I invented it my- 

 felf in Burgundy, where, in the time of the academy of Dijon, it was confidercd as the beft 

 inilrument, on a fmall fcale, for determining the ftrength of gunpowder. 



Defcription. Plate IX. fig. I. A. A perfpedive view of the inftrument. B. C. A fpring 

 bended into an angle. D. A fmall cannon of brafs, containing exa£liy a gramme of fine 

 gunpowder (15J grs). E. Arc of divifion graduated into kilogrammes (nearly albs and 

 a quarter avoirdupois each), terminating in a fcrew, which ferves as the breech-pin to the 

 cannon. F. A cap, which may be confidered as the proje6lile. It clofes the mouth of 

 the fmall cannon, upon which it prefles with a force equal to four kilogrammes. 'I'his 

 ftopper is firmly fixed to one of the fpring radii, by means of a nut at the oppofite end of its 

 branch or tail. G. A piece of hard brafs wire fixed to a projeflion, rivetted into one of the 

 radii, by means of a fmall fcrew. H. An index of woollen cloth, or leather, which Aides 

 by a gentle friflion upon the wire, when the branches of the fpi ing are preffed together by 

 the inflammation of the powder. This index remains at the place to which it has been 

 pufhed, and fhews precifely the diftance to which the fprings have been made to approach. 



Method of ufing this inftrument. i. The two extremities of the fpring are to be preflld- 

 together, in order to feparate the cap from the mouth of the fmall cannon. 2. Powder is 

 poured either by means of card or paper into the cannon, fo as exadly to fill it; the ftopper is 

 then fuffered to apply itfelf gently to the muzzle, and clofe it exaftiy, without leaving any 

 grain of powder between them. 3. The circular piece of cloth, or leather, which ferves as 

 the index, muft be moved into conta£t with that branch of the fpring, to which the tail 

 of the ftopper is fixed. 4. Priming being then put into the fmall pan of the cannon, it mult 

 be difcharged, holding the inftrument fufpended by the ribband or ftring which is pafTcd 

 through the angular bend. 



The effcdls of the explofion are, that the powder occupying a greater fpace by its inflam- 

 mation, drives back the ftopper, which carries with it that branch of the fpring in which its 

 tail is firmly fixed. This branch cannot move relatively to the other, which is alfo moved by 

 the recoil of the gun, without driving before it the fmall index piece, and the fpace through 

 which this is carried will fliew the force of the powder. 



The arcs moved through by the explofion of difterent famples of powder, will ftiew, by the 

 numbers of their graduations, the comparative forces of each. There is a ftar marked on 

 the graduated arc which ftiews the force of powder of a medium quality, in order that t!ie 

 •relative value of any faoiple, with regard to that medium, may be known. The friction 

 cf the index is the only friction to which this inftrument is fubjedj and this is fo flight, that 

 it may be confidered as nothiri'^. The index itfelf may be eafily renewed when worn out- 



D d 2 It 



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