The author distinguished between fixed CO2, assumed to be in the form of bicarbonate and carbonate ion, and unfixed CO2, assumed to be in the form of CO2(aq) and H2CO3(aq).The author found that the fixed dissolved carbon dioxide did not vary with temperature while the unfixed dissolved carbon dioxide decreased as temperature increased. He summarized these results in the following table.
The carbon dioxide solubilities in water correspond to mole fraction solubilities of 5.83 x 10-4 and 3.02 x 10-4 at one atm assuming the density of water and the CO2 saturated solutions have the same value.
a The common name of the electrolyte is diammonium citrate.
b Added by the compiler. The Kelvin temperatures are not intended to represent an accuracy, but to reproduce the Fahrenheit temperatures.
c The pH given for water (c2/mol L-1 = 0) means pH of water saturated with carbon dioxide. According to the author the measurements showed that saturating water with CO2 under the ambient barometric pressure in the temperature range of 80 to 140 °F yielded a pH of 4.2 ± 0.1.The ammonium citrate solutions of certain pH's were prepared as follows:
At pH 4 the solution was prepared from an equimolar mixture of citric acid and diammonium citrate to contain 11.1 g/L of monoammonium citrate, and its pH was adjusted upward to pH 4 by adding ammonia.
At pH5 the solution was primarily diammonium citrate and was prepared by dissolving 12 g of diammonium citrate per liter.
At pH 6 and at pH 7 ammonia was added to the pH 5 solution. At pH 7 the salt was in the form of triammonium citrate.
All solutions were initially prepared to contain 12 g diammonium citrate per liter (0.053 mol L-1).
d The values for the solubility of CO2 in water are at a total pressure of 1 atm (101.3 kPa). The carbon dioxide in ammonium citrate solutions was measured at a barometric pressure of 730 mmHg (0.960 atm or 97.3 kPa).