. Radio-activity . perature observed will obviously depend uponthe size and nature of the vessel con- _ taining the radium. During their visit to England in1903 to lecture at the Royal Insti-tution, M. and Mme Curie performedsome experiments with ProfessorDewar, to test by another method therate of emission of heat from radiumat very low temperatures. This methoddepended on the measurement of theamount of gas volatilized when aradium preparation Avas placed insidea tube immersed in a liquefied gasat its boiling point. The arrange-ment of the calorimeter is shown inFig. 97. The small closed Dew
. Radio-activity . perature observed will obviously depend uponthe size and nature of the vessel con- _ taining the radium. During their visit to England in1903 to lecture at the Royal Insti-tution, M. and Mme Curie performedsome experiments with ProfessorDewar, to test by another method therate of emission of heat from radiumat very low temperatures. This methoddepended on the measurement of theamount of gas volatilized when aradium preparation Avas placed insidea tube immersed in a liquefied gasat its boiling point. The arrange-ment of the calorimeter is shown inFig. 97. The small closed Dewar flask A contains the radium in a glasstube R, immersed in the liquid to be employed. The flask A issurrounded by another Dewar bulb B, containing the same liquid,so that no heat is communicated to A from the outside. The gasliberated in the tube A is collected in the usual way over water ormercury, and its volume determined. By this method, the rateof heat emission of the radium was found to be about the same in. Fig. 97. * Runge and Precht, Sitz. Ah. Wiss. Berlin, No. 38, P. Curie, Societe de Physique, 1903. XIl] RATE OF EMISSION OF ENERGY 421 boiling carbon dioxide and oxygen, and also in liquid interest attaches to the result obtained with liquidhydrogen, for at such a low temperature ordinary chemical ac-tivity is suspended. The fact that the heat emission of radiumis unaltered over such a wide range of temperature indirectlyshows that the rate of expulsion of a particles from radium isindependent of temperature, for it will be shown later that theheating effect observed is due to the bombardment of the radiumby the a particles. The use of liquid hydrogen is very convenient for demonstrat-ing the rate of heat emission from a small amount of 0*7 gram of radium bromide (which had been prepared only10 days previously) 73 of gas were given off per minute. In later experiments P. Curie (loc. cit.) found that the rate ofemission of hea
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