Abstract
Full constructional details are given for an effusion cell in Armco iron, which in conjunction with a calibrated glass spring and cathetometer has been used to measure the vapour pressure over solid ferric chloride in the temperature range 100-200° C. The chief advantage claimed for the cell is that the effusion orifices, in interchangeable push fit end-caps, are of the form of true circular knife edged holes with easily determined dimensions.