. Radio-activity . thecoefficient of diffusion of the emanation into air is found to havea value, lying between that of two known gases A and B, it isprobable that the molecular weight of the emanation lies betweenthat of A and B. Although the volume of the emanation given off from radiumis very small, the electrical conductivity produced by the emanationin the gas, with which it is mixed, is often very large, and offersa ready means of measuring the emanation present. Some experiments have been made by Miss Brooks and thewriter* to determine the rate of the diffusion of the radium emana-* Eut
. Radio-activity . thecoefficient of diffusion of the emanation into air is found to havea value, lying between that of two known gases A and B, it isprobable that the molecular weight of the emanation lies betweenthat of A and B. Although the volume of the emanation given off from radiumis very small, the electrical conductivity produced by the emanationin the gas, with which it is mixed, is often very large, and offersa ready means of measuring the emanation present. Some experiments have been made by Miss Brooks and thewriter* to determine the rate of the diffusion of the radium emana-* Eutherford and Miss Brooks, Trans. Roy. Soc. Canada 1901, Chem. News 1902. 270 RADIO-ACTIVE EMANATIONS [CH. tion into air, by a method similar to that employed by Loschmidt*in 1871, in his investigations of the coefficient of inter-diffusionof gases. Fig. 56 shows the general arrangement. A long brass cylinderA B, of length 73 cms., and diameter 6 cms., was divided into two Electrometer Batjery ^ ■k ^ t B I[L ||_A_. Electrometer Eadium Fig. 56. equal parts by a moveable metal slide S. The ends of the cylinderwere closed with ebonite stoppers. Two insulated brass rods, aand h, each half the length of the tube, passed through the ebonitestoppers and were supported centrally in the tube. The cylinderwas insulated and connected with one pole of a battery of 300volts, the other pole of which was earthed. The central rods couldbe connected with a sensitive quadrant electrometer. The cylinderwas covered with a thick layer of felt, and placed inside a metalbox filled with cotton wool in order to keep temperature con-ditions as steady as possible. In order to convey a sufficient quantity of emanation intothe half-cylinder A, it was necessary to heat the radium slide S was closed and the side tubes opened. A slowcurrent of dry air from a gasometer was passed through a platinumtube, in which a small quantity of radium compound was emanation was carried with the air
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