YovNQ—Vii.poirr- Pressures, iSfc, of Tkirtij Pure Substances. 393 



stand as the iron tube. The screw can be turned by means of the circular 

 handle, E, and the capacity of the iron vessel thus increased or diminished. 



Each of the vertical branches, 

 like tlie liorizontal tube, is provided 

 with a steel ring and perforated 

 screw, and through each screw and 

 ring passes a thick-walled glass tube 

 of about 1-5 mm. internal diameter, 

 kept in position by an enlargement 

 which presses against a leather 

 waslier fitting the bottom of the 

 screw. Each of these stufiSng-boxes 

 contains a well-greased, perforated, 

 cylindrical india-rubber stopper, 

 which rests on a greased leather 

 washer, fitting the upper side of the 

 steel ring. The glass tubes are 

 closed above, but open below ; they 

 are all graduated in millimetres 

 G and carefully calibrated ; two of 

 them serve as air-manometers. The 

 internal diameter of one of them, 

 F, which serves for the measurement 

 of moderate pressures, is the same 

 throughout ; that of the lower end 

 of the other, Q, which is intended 

 for high pressures, is much greater, 

 so that this tube is provided with 

 a reservoir of relatively great capa- 

 city. The third or " experimental " 



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