for the Pressure of Uglily compressed Steam, Gases, %c. 37 



Description, Sfc. 



Considerable difficulty has been experi- 

 enced in acertaining in a satisfactory man- 

 ner the exact pressure of highly condensed 

 gases or fluids. 



The usual method of accomplishing this 

 object is by the rising of a column of mer- 

 cury in a glass tube hermetically sealed at 

 the top; the tube being previously filled 

 with air at the ordinary pressure of the at- 

 mosphere. For as the mercury rises by the 

 pressure of the gas, the air confined in the 

 tube above the surface of the mercury will 

 be compressed to the same degree as the gas 

 itself, making proper allowance for the weight 

 of the column of mercury. But it happens 

 that when fluids are required to be com- 

 pressed to 30 or 40 atmospheres, it becomes 

 necessary to have the tube of the mercury 

 gauge of very great length, say from 30 to 

 45 feet, otherwise the divisions of the upper 

 part of the scale will be much too small for 

 useful reference ; but this great length ren- 

 ders the apparatus exceedingly inconvenient 

 for practical purposes. 



The accompanying drawing represents a 

 gauge on an improved principle, which it is 

 expected will be found much more conveni- 

 ent and correct than the gauge in common 

 use. The gauge consists of two small cylin- 

 drical chambers A and B, and the glass 

 tube C. The communication between the 

 two is by the small tube d, which reaches 

 nearly to the bottom of the lower chamber. 

 The glass tube C we will suppose to be 

 about eight feet long : the chamber B is to 

 be filled with mercury as high as the line cc; 

 the tube e is to admit the compressed gas 

 or fluid, which acting on the surface of the 

 mercury forces it up the tube d, which after 

 filling the chamber A will rise in the tube C. 

 Now, supposing the apparatus to be pre- 

 viously rilled with air of the common atmo- 

 spheric pressure, and that the chamber A 

 be equal to ID times the capacity of the 



tube 



