UNIT OF PRESSURE 



43 



culty is now increased by the frequent technical use of this word to 

 designate the pressure of a kilogram per square centimeter. The 

 growing tendency toward the adoption of the c.g.s. system suggests 

 the use of a consistent unit for this dimension also. Might not the 

 pressure of a dyne per square centimeter be suitably called a bar? 

 (Greek /?a/>?, pressure, weight.) This suggestion is made because the 

 practical use of a unit is always much facilitated by a definite verbal 

 designation. In this case, the pressure of a megadyne per square cen- 

 timeter would be called a megabar, a name no more cumbrous than 

 atmosphere, and far more definite. This unit, though unnamed, has 

 long been advocated by Ostwald as a more scientific one than the 

 present standard. 1 The megabar is 1,000/980.6 = 101.98 per cent, of 

 a kilogram per square centimeter, or 101.98/1,033.2 = 98.703 per cent. 

 of an atmosphere, or the pressure measured by 7^.01=5 centimeters of 

 mercury at o C, at sea level, and 45 of latitude. This pressure is 

 more nearly the average atmospheric pressure at the laboratories of the 

 world than the arbitrary atmosphere usually taken. A megabar, act- 

 ing through the volume of a cubic centimeter or milliliter, performs a 

 megerg of work, or one-tenth of a joule. For the convenience of pos- 

 sible users of the new results, all are tabulated below on the basis of 

 each one of these three standards of pressure. 



Table of Compressibilities at 20 C. 

 The values given below are multiplied by io 5 in order to economize space. 

 Brackets signify partial extrapolation. 



1 Grundriss allgem. Chem., p. 54 (1899). 



