Dear Jim and All, Re: Matthew Zotter's original question
This is a reverse chronology and refers only to pressure. Could you check if I've got this right, please? 2002 The 'standard conditions for gases' now implies a pressure of 100�000�pascal. This is the IUPAC standard but not necessarily the IUPAP standard. 1993 IUPAC defined 'standard conditions for gases' with a pressure of '10^5�pascals'. 1990 IUPAC reported that the pressure 10^5 Pa was usually employed in reporting gas volumes for 'STP', the abbreviation for standard temperature and pressure. 1986 CODATA defined a 'standard atmosphere' as having a pressure of 101�325�Pa. 1982 IUPAC recommended the value 10^5 Pa for atmospheric pressure. 1954 The 10th CGPM declared 101 325 Pa to be the pressure of a 'standard atmosphere' for general use. 1948 The 9th Conf�rence G�n�rale des Poids et Mesures defined 101 325 newtons per square metre as the standard atmosphere for accurate work in thermometry (the old 760 mm of mercury). *** It looks a lot like the CGPM simply converted 760 mm of mercury (mmHg) to 101�325�newtons per square metre (with a somewhat dubious precision of six significant figures). In turn, it looks a lot like 760 millimetres of mercury was a casual rounding of 30 inches of mercury to a metric measure (30 inches x 25.4 mm/inch = 762 millimetres) Which leaves us with Matthew Zotter's original question, 'What society defined standard atmospheric pressure ... ' I suppose that the original meteorologists simply looked at the range of pressures on their charts (at sea level) and guessed that 30 inches of mercury was somewhere near the middle. If we did the same experiments today � with a manometer* calibrated in pascals we would guess that the value 100�000 pascals was somewhere near the middle of the range. Doesn't it take a long while to make a simple change. Cheers, Pat Naughtin CAMS Geelong, Australia * I avoided the use of the word barometer because I did not want to get embroiled in a discussion about machines that measure bars!
