The coefficient of diffusion _K_ of the emanation into the liquid can be obtained from the same equation used to determine the diffusion of the thorium emanation into air, $$ p = p₀ e^{-\sqrt {\frac {λ} {K} x}} $$ . where λ is the constant of decay of activity of the radium emanation and _x_ the depth of the layer of water from the surface. Putting $$ a = \sqrt {\frac {λ} {K}} $$, it was found that for water α = 1·6, for toluol α = ·75. The value of λ expressed in terms of a day as the unit of time is about ·17. Thus the value of _K_ for the diffusion of the radium emanation into water = ·066 cm.² / day. The value of _K_ found by Stefan[260] for the diffusion of carbon dioxide into water was 1·36 cm.²/day. These results are thus in harmony with the conclusion drawn from the diffusion of the radium emanation into air, and show that the radium emanation behaves as a gas of high molecular weight. Condensation of the Emanations. =165. Condensation of the emanations.= During an investigation of the effect of physical and chemical agencies on the thorium emanation, Rutherford and Soddy[261] found that the emanation passed unchanged in amount through a white-hot platinum tube and through a tube cooled to the temperature of solid carbon dioxide. In later experiments the effects of still lower temperatures were examined, and it was then found that at the temperature of liquid air both emanations were condensed[262]. If either emanation is conveyed by a slow stream of hydrogen, oxygen, or air through a metal spiral immersed in liquid air, and placed in connection with a testing vessel as in Fig. 51, no trace of emanation escapes in the issuing gas. When the liquid air is removed and the spiral plunged into cotton-wool, several minutes elapse before any deflection of the electrometer needle is observed, and then the condensed emanation volatilizes rapidly, and the movement of the electrometer needle is very sudden, especially in the case of radium. With a fairly large amount of radium emanation, under the conditions mentioned, a very few seconds elapse after the first sign of movement before the electrometer needle indicates a deflection of several hundred divisions per second. It is not necessary in either case that the emanating compound should be retained in the gas stream. After the emanation is condensed in the spiral, the thorium or radium compound may be removed and the gas stream sent directly into the spiral. But in the case of thorium, under these conditions, the effects observed are naturally small owing to the rapid loss of the activity of the emanation with time, which proceeds at the same rate at the temperature of liquid air as at ordinary temperatures.