2002-11-24 Why 105 kPa for 1 atmosphere of pressure? What reference or experiment would back this up? If it is just a random number, then why not choose 100 kPa?
There is also something to be said for 4�C. It is the temperature at which water has its maximum density of 1000 kg/m^3. John ----- Original Message ----- From: "James R. Frysinger" <[EMAIL PROTECTED]> To: "U.S. Metric Association" <[EMAIL PROTECTED]> Sent: Sunday, 2002-11-24 14:34 Subject: [USMA:23559] Re: atmosphere and gravity and more I found the homepage of the IUPAC. It's at http://iupac.chemsoc.org/dhtml_home.html Using their resources I found the following, *non-SI* definitions: ***standard atmosphere Pressure defined as 101 325 Pa and used as unit of pressure with the symbol atm. CODATA Bull., 1986, 63, 1; 1996, 68, 993 IUPAC Compendium of Chemical Terminology 2nd Edition (1997) ***standard pressure Chosen value of pressure denoted by p or p�. In 1982 IUPAC recommended the value 105 Pa, but prior to 1982 the value 101 325 Pa (= 1 atm) was usually used. G.B. 54; 1994, 66, 536 IUPAC Compendium of Chemical Terminology 2nd Edition (1997) ***STP Abbreviation for standard temperature (273.15 K or 0 �C) and pressure (105 Pa); usually employed in reporting gas volumes. Note that flow meters calibrated in standard gas volumes per unit time often refer to volumes at 25 �C, not 0 �C. See also standard conditions for gases. 1990, 62, 2217 IUPAC Compendium of Chemical Terminology 2nd Edition (1997) ***standard conditions for gases Temperature, 273.15 K (�C) and pressure of 10^5 pascals. IUPAC recommends that the former use of the pressure of 1 atm as standard pressure (equivalent to 1.01325 x 10^5 Pa) should be discontinued. See STP. 1990, 62, 2216 IUPAC Compendium of Chemical Terminology 2nd Edition (1997) So, this seems to be pretty much an IUPAC thing. The "standard atmosphere" brings in IUPAP, the other big player in the CODATA referred to in the first definition. "GB" refers to G.B. (Green Book) IUPAC Quantities, Units and Symbols in Physical Chemistry. Second Edition, Blackwell Scientific Publications, Oxford, 1993. Citations above without a CODATA or GB reference are to the Journal of Pure and Applied Chemistry. See http://www.iupac.org/publications/compendium/index.html for more details. While I'm at it, the homepage for IUPAP is at http://www.iupap.org/ Jim "James R. Frysinger" wrote: > > > Matthew Zotter wrote: > > > > 2002 NOV 24 SUN > > > > What society defined standard atmospheric pressure to be 101.325 kPa > > (I know the value came from 760 torr) and standard gravity to be > > 9.80665 m/s^2? Is standard room temperature 293.15K or 298.15 K or > > both? Do any of you know were I could get a thermometer that reads in > > kelvins. > "Standard Temperature and Pressure (STP)" was defined at one time by > the International Union of Pure and Applied Chemistry (IUPAC). Perhaps > they were joined in that by the IUPAP (same thing but for Physics). I > don't know if those are still accepted definitions with that field (or > fields if physics is included), but at least in physics I hardly ever > see that term used. The SI values for those defined parameters are > 101.325 kPa and 273.15 K. > > The SI brochure does not define STP. However, one sees those the > equivalent value for Standard Pressure in the appendix of the brochure, > specifically on page 123, clause 2.5, the entry for the 10th CGPM > Resolution 4 (1954). This is of course pre-SI, but I see nothing > abrogating it. Let's face it, the SI folks have pretty much gotten away > from defining standard values of anything except those needed to define > units (e.g., the definition of the candela). .... -- Metric Methods(SM) "Don't be late to metricate!" James R. Frysinger, LCAMS http://www.metricmethods.com/ 10 Captiva Row e-mail: [EMAIL PROTECTED] Charleston, SC 29407 phone: 843.225.6789
