TRANSITION TEMPERATURES OF THE HYDRATES OF Na2SO4, Na2HPO4, AND KF AS FIXED POINTS IN BIOMEDICAL THERMOMETRY.

Abstract

The hydrate transition temperatures of Na//SO//4 multiplied by (times) 10H//2O to Na//2SO//4, KF multiplied by (times) 2H//2O to KF, and Na//2HPO//4 multiplied by (times) 7H//2O to Na//2HPO//4 multiplied by (times) 2H//2O were established using ACS grade salts as 32. 374 degree C, 41. 422 degree C, and 48. 222 degree C, respectively. A simple and reliable procedure involving inexpensive materials was used to realize these transitions as temperature fixed points. Each transition temperature was attained within 30 minutes of hydrate initiation and remained constant to within plus or minus 0. 002 degree C for more than 10 hours if the mixture was stirred. The established transition temperatures were sensitive at the 0. 001 degree C level to the amount of impurities, so the materials used should be of the highest quality available. These systems fill a gap in the existing spectrum of temperature standards and should be useful in biomedical laboratories for calibrating thermometers.