. Radioactive transformations . d byhim in his measure-ments. The percentageof uranium in the min-eral under considerationwas first determined bychemical analysis. Aknown weight of thefinely powdered mineralwas placed in a glassvessel A (Fig. 39), andsufficient acid intro-duced to dissolve it. The acid was thenboiled until the mineralwas completely dis-solved, and the emana-tion mixed with air was collected on the top of the column ofwater in the tube D. This emanation was then introduced intoa closed electroscope of the type shown in Fig. 6, page 29, whichwas first exhausted. Air was then int
. Radioactive transformations . d byhim in his measure-ments. The percentageof uranium in the min-eral under considerationwas first determined bychemical analysis. Aknown weight of thefinely powdered mineralwas placed in a glassvessel A (Fig. 39), andsufficient acid intro-duced to dissolve it. The acid was thenboiled until the mineralwas completely dis-solved, and the emana-tion mixed with air was collected on the top of the column ofwater in the tube D. This emanation was then introduced intoa closed electroscope of the type shown in Fig. 6, page 29, whichwas first exhausted. Air was then introduced until the gasinside the electroscope was at atmospheric pressure. On ac-count of the excited activity produced by the emanation, therate of discharge of the electroscope did not reach a maximumuntil about three hours after the introduction of the emana-tion. The rate of movement of the gold leaf of the elec-troscope was taken as a measure of the amount of emanationpresent. The emanations of thorium or actinium, released. 154 RADIOACTIVE TRANSFORMATIONS from the mineral at the same time as the radium emanation,had, on account of the rapid decay of their activity, completelydisappeared before the introduction of the radium emanationinto the electroscope. This process was repeated for all theminerals examined. Boltwood observed that some minerals had considerable eman-ating power, i. e., the minerals lost some of their emanationwhen in the solid state. Under these conditions, the amountof emanation released by solution and boiling of the mineralwould be less than the equilibrium amount. The proper correc-tion was made by sealing up a known weight of the mineral in atube for one month and then measuring with the same electro-scope the amount of emanation which collected in the air abovethe mineral. The sum of the two amounts gives the trueequilibrium quantity of emanation corresponding to the radiumpresent in the mineral. The results obtained by Boltwood are shown in the fo
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