Fig. 10.
A diagram of the visible lines of the spectrum of the elements Radium and Helium—when rendered incandescent by electric ‘sparking’ in a glass tube: kindly prepared for this book by Mr. Frederick Soddy of the University of Glasgow. The position of the chief great lines of the solar spectrum are marked on the lowest horizontal line. On the upper line the wave-lengths of the rays occupying the position indicated, are given. The figure 72 means that the wave-length of the ray occupying this position when refracted by the prism of the spectroscope is, as measured from crest to crest of the undulation, seven hundred and twenty millionths of a millimetre. It is generally written 720·0 µµ.
Lines exist at the ultra-violet end of the spectrum which can be photographed but do not affect the eye—that is to say are invisible. On the other hand the lines of the red end of the spectrum do not produce a photographic effect. Consequently a ‘photographed’ spectrum such as that given in the next figure ([fig. 11]) differs in the lines presented both at the red and the violet ends from the visible series of lines. The two (visible and photographed spectra) agree only from wave-length 587·6 µµ to wave-length 447·2 µµ.
The two spectra given in fig. 10 show how great is the difference in the position and number of the bands of Radium and Helium—yet as shown in the next figure ([fig. 11]) the ‘emanation’ from Radium actually is transformed into Helium.
The atomic weight was determined in the usual way by precipitating the chlorine in a solution of radium chloride by means of silver. None of the precious element was lost in the process, but the Curies never had enough of it to venture on any attempt to prepare pure metallic radium. This is a piece of extravagance no one has yet dared to undertake. Altogether the Curies did not have more than some four or five grains of chloride of radium to experiment with, and the total amount prepared and now in the hands of scientific men in various parts of the world probably does not amount to more than sixty grains at most. When Professor Curie lectured on radium four years ago at the Royal Institution in London he made use of a small tube an inch long and of one-eighth bore, containing nearly the whole of his precious store, wrenched by such determined labour and consummate skill from tons of black shapeless pitch-blende. On his return to Paris he was one day demonstrating in his lecture room with this precious tube the properties of radium when it slipped from his hands, broke, and scattered far and wide the most precious and magical powder ever dreamed of by alchemist or artist of romance. Every scrap of dust was immediately and carefully collected, dissolved, and re-crystallized, and the disaster averted with a loss of but a minute fraction of the invaluable product.
Thus, then, we have arrived at the discovery of radium—the new element endowed in an intense form with the new property ‘radio-activity’ discovered by Becquerel. The wonder of this powder, incessantly and without loss, under any and all conditions pouring forth by virtue of its own intrinsic property powerful rays capable of penetrating opaque bodies and of exciting phosphorescence and acting on photographic plates, can perhaps be realized when we reflect that it is as marvelous as though we should dig up a stone which without external influence or change, continually poured forth light or heat, manufacturing both in itself, and not only continuing to do so without appreciable loss or change, but necessarily having always done so for countless ages whilst sunk beyond the ken of man in the bowels of the earth.