In the rather simple working up of the raw material containing radium, the treatment of barium has in the main been followed. Subsequently, the utilization of certain differences in solubility has permitted fractional crystallization and we have thus learned of a special spectrum of radium. But it is questionable whether the spectrum reaction can claim a decisive weight. For a substance, which in so minute proportions has been extracted from so complex a material as the residuals of Joachimsthal, the spectrum might readily prove deceptive. There seems to be very little correspondence between the spark-spectrum for radium obtained by Demarcay, and the flame spectrum described by F. Giesel, while the reddish-orange lines in the radium bromide spectrum, as well as the red coloration which this substance imparts to the flame, make it not impossible that some alkaline earths may have remained in the final residue examined. Besides, no radium compounds have been sufficiently investigated, nor have any chemical reactions been detected specifically peculiar to radium. The determination of its atomic weight has been decisive in recognizing radium as a distinct element, especially as this atomic weight was found to be exceptionally high.
Radium lead has been examined chemically more thoroughly, and yet no noteworthy differences have been discovered between its reactions and those of common lead. Only a great difference in atomic weight seemed to exist. The atomic weight of radiolead was determined by ascertaining the amount of sulphuric acid in its sulphate. It was found to contain 41.85 per cent, of SO4, while lead sulphate contains only 31.71 per cent.
Assuming that radiolead is quadrivalent like thorium and uranium, its atomic weight from the above analysis would be 260.2, that of lead only 206.9. But this determination seems of doubtful correctness, because the sulphate obtained has not been heated to a beginning redheat, but has only been dried to 400-420 degrees. At so low a temperature experience has shown it is impossible to remove all adherent sulphuric acid, so that it is not strange that a higher per cent, of sulphuric acid remained. The atomic weight of radiolead can not be deduced from such determinations. Also the supposed discovery of other elements (such as the much hunted for ekamanganese of Mendelejef) can not be established upon the result of such faulty determinations.
Indeed the chemical researches made can not be considered sufficient, however much we may admire the other researches made on the radioactivity of matter. Even the results obtained by fractioning can only be used with extreme caution, because they may lead easily to false conclusions. When the discovery of spectrum analysis had excited the scientific world as it is to-day excited by that of radioactivity, it was
