A balance method is described for accurately comparing quantities of radium by their γ-radiation, in which the ionisation due to the γ-rays is balanced against the constant ionisation due to uranium oxide. By observing the distance of the radium preparation from the ionisation chamber when a balance is obtained, the relative γ-ray activities of the two preparations can be determined with an accuracy of at least one part in 400. A method of calibration is given, and the corrections necessary to deduce the quantities of radium present are considered. Calculations are given showing the correction required to determine a quantity of emanation by comparison of its γ-ray activity with that due to a radium standard. The balance method was employed to determine the period of transformation of the radium emanation. The half value period was found to be 3.854 days. It was found experimentally that the γ-ray activity due to the radium emanation and its products reaches a maximum 255 minutes after the introduction of the emanation into a sealed tube. Calculations showed that under the experimental conditions the theoretical maximum should be reached after 255 minutes. It was found that the γ-ray activity of a radium preparation was not appreciably altered by exposure in a strong magnetic field.