Abstract
The measurements on the growth of radium in the three uranium solutions purified by Mr. T. D. Mackenzie between three and four years ago have shown that in all the growth of radium is proceeding at a rate proportional to the square of the time within the error of measurement. The methods of testing have been improved and the ordinary error is not greater than 10-12 gram of radium. This result indicates the existence of only one long-lived intermediate product in the series between uranium and radium. The period of average life of this body, calculated on the assumption that no other intermediate bodies exist, is 18,500 years in the case of the oldest solution for which data are available over a period from the end of the third to the end of the fourth year from purification. But for the solution prepared last, over a period from the end of the second to the end of the third year, the period indicated is about half again as long as in the first experiment. Indeed, had this solution grown radium at the same rate, with reference to the square of the time, as the older solution has been doing during the past year, more radium should have been formed than the total amount now actually present. This suggests the existence of at least one new intermediate product in the series "Uranium A" with a period comparable to the time observations have been in progress. From a mathematical investigation of the effect of such a body on the rate of growth of radium, it is concluded that it would not, if it existed, appreciably alter the production of radium according to the square of the time over the period accurate observations have been made, even were the period of the new body as great as four years. But its existence would vitiate the calculation of the period of the direct parent of radium according to the simple formula neglecting short-lived products. Other evidence on the problem is contained in the next paper (Rays and Product of Uranium X).