Isotherms of CO 2 between 0° and 150° and pressures from 16 to 250 atm (Amagat densities 18-206)

Abstract

In a previous publication* results of measurements were given of the dielectric constant of CO 2 under pressure. In the calculation of the Clausius-Mosotti function, ε-1/ε+2. 1/ d , from these results and the isotherm data as published by Amagat doubt arose as to the reliability of the latter, and isotherrn measurements have therefore been carried out up to 3000 atm at the same temperature at which the dielectric constant was measured. The results will be given in series of papers, of which the present one describes the measurements up to 250 atm. In this range the method published in previous papers could be used. The apparatus is shown diagrammatically in fig. 1. A is the glass piezometer containing the gas under investigation. It is enclosed in the steel vessel C, which contains some mercury, the remainder being filled with oil. The piezometer consists of a large reservoir B and several small reservoirs connected by narrow capillaries. Through each of these capillaries is sealed a platinum wire, and these all make contact with another platinum wire wound round the outside of the capillary and connected to an insulated lead E through the top of the steel vessel. The volumes from each of the contact to the top of the tube are calibrated by weighing with mercury, using the method described by Michels and Gibson. The volume of gas with which the piezometer is filled is determined separately at 25° and a pressure of about 1 atm, as described by Michels, Wouters, and de Boer. The steel vessel is placed in a thermostat, the temperature of which is electrically regulated in the way previously described by the authors. The temperature is read with thermometers divided in hundredths of a degree and compared with thermometers calibrated at the P. T. R. (Berlin). They were totally immersed in the thermostat and read with the help of a periscope. For the isotherm measurements, pressure is applied to the oil through D, forcing the mercury up inside the piezometer and compressing the gas till the mercury surface makes contact with the platinum wires. This contact is indicated by a drop in the electrical resistance of the platinum wire wound round the capillary. The equilibrium pressure, at which contact is made, is measured with a pressure balance. Corrections must be applied for the height of the mercury column inside the glass piezometer and the hydrostatic head of the oil. From the data thus obtained for p, v , and T, the isotherm can be calculated if the total amount of gas contained in the piezometer is known in standard units.