116 Immerffe Force of Steam. [Book II. 



which compreffcs it. Its force in refitting compref- 

 fion, when it is accumulated to a certain degree, is 

 however greater than that of gunpowder, or of any 

 power widi which we are acquainted. Steam is there- 

 fore one of the moft potent and mod dangerous agents 

 in nature. A fmall quantity of water thrown upon 

 boiling oil, or introduced among metals while in fu- 

 fion, produces the moft formidable effects. The wa- 

 ter finks towards the bottom in the oil, where being 

 converted into vapour, by the force of its expanfion it 

 caufes a moft violent ebullition and explofion, and 

 throws the heated fluid about with incredible velocity. 

 Hence in cafting iron or copper velTels, if the fmalleft 

 particle of humidity is contained in the mold, or if the 

 metal meets with any liquid in its paflage from the 

 furnace to the mold, it will be exploded with the ut- 

 moft hazard to the workmen from the burning metal. 

 We iiave an inftance recorded in the Philofophical 

 Tranfac~lions, of the burfting of one of Papin's digeft- 

 crs containing a pint of water, which demonftrates the 

 amazing expanfive force of vapour. The report on 

 the burfting of the veffel was heard at a confiderable 

 diftance by a maid fervant who was milking the cows 

 in an adjacent field, and the fervants within faid it 

 fhook the houfej the veflel flew in a direct line acrofs 

 the room, and Ihivered an inch plank of oak in pieces: 

 what is moft extraordinary, no traces of water were to 

 be found in any part of the room ; the fire was how- 

 ever completely extinguifhed *. 



The force of the common fleam engine is well 

 known f ; and an inftance recorded by Mr. Jones in 



his 



* Phil. Tr. Abr. vol. viii. p. 465. 



f In thefe machines, the fteam is conveyed into a large cylin- 

 der or barrel of iron, in which a very heavy pifton of the fame 



metal 



