. Radio-activity . t had longbeen known that radium compounds increased in activity for abouta month after their preparation, when they reached a steady has been shown (section 215), that this increase of activity isdue to the continuous production by the radium of the radio-active emanation, which is occluded in the radium compound andadds its radiation to that of the radium proper. It thus seemedprobable that the heating effect was in some way connected withthe presence of the emanation. Some experiments upon this pointwere made by Rutherford and Barnes*. In order to measure thesmal
. Radio-activity . t had longbeen known that radium compounds increased in activity for abouta month after their preparation, when they reached a steady has been shown (section 215), that this increase of activity isdue to the continuous production by the radium of the radio-active emanation, which is occluded in the radium compound andadds its radiation to that of the radium proper. It thus seemedprobable that the heating effect was in some way connected withthe presence of the emanation. Some experiments upon this pointwere made by Rutherford and Barnes*. In order to measure thesmall amounts of heat emitted, a form of differential air calo-rimeter shown in Fig. 98 was employed. Two equal glass flasks * Rutherford and Barnes, Nature, Oct. 29, 1903. Phil. Mag. Feb. 1904. 422 RATE OF EMISSION OF ENERGY [CH. of about 500 were filled with dry air at atmospheric flasks were connected through a glass U-tube filled withxylene, which served as a manometer to determine any variation. Fig. 98. of pressure of the air in the flasks. A small glass tube, closedat the lower end, was introduced into the middle of each of theflasks. When a continuous source of heat was introduced into theglass tube, the air surrounding it was heated and the pressure wasincreased. The difference of pressure, when a steady state wasreached, was observed on the manometer by means of a microscopewith a micrometer scale in the eye-piece. On placing the sourceof heat in the similar tube in the other flask, the difference inpressure was reversed. In order to keep the apparatus at aconstant temperature, the two flasks were immersed in a water-bath, which was kept well stirred. Observations were first made on the heat emission from 30milligrams of radium bromide. The difference in pressure observedon the manometer was standardized by placing a small coil of wireof known resistance in the place of the radium. The strength ofthe current through the wire was adjusted to give the sa
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