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 *cussed, point to the conclusion that the emanation is of high molecular weight. There can thus be no doubt that the helium is derived from the emanation of radium in consequence of changes of some kind occurring in it.

These results were confirmed later by other observers. Curie and Dewar performed the following experiment: A weight of about ·42 gr. of radium bromide was placed in a quartz tube, and the tube exhausted until no further gas came off. The radium was then heated to fusion, about 2·6 c.c. of gas being liberated in the process. The tube was then sealed, and some weeks afterwards the spectrum of the gas liberated in the tube by the radium was examined by Deslandres and found to give the entire spectrum of helium. The gas, liberated during the initial heating of the radium, was collected and found to contain a large amount of emanation, although the gas had been passed through two tubes immersed in liquid air. The tube containing these gases was very luminous and rapidly turned violet, while more than half of the gases was absorbed. The spectrum of the phosphorescent light was found to be discontinuous, consisting of three nitrogen bands. No sign of the helium spectrum was observed, although helium must have been present.

Himstedt and Meyer placed 50 mgrs. of radium bromide in a U tube connected with a small vacuum tube. The tube was carefully exhausted and then sealed off. The spectrum of hydrogen and carbon dioxide alone was observed for three months, but after four months the red, yellow, green and blue lines of the helium spectrum were visible. The slow appearance of the helium spectrum was probably due to the presence in the tube of a considerable quantity of hydrogen. In another experiment, some radium sulphate which had been heated to a bright red heat in a quartz tube was connected with a small vacuum tube. After three weeks, some of the lines of helium were clearly seen, and increased in brightness with time.

268. Connection between helium and the α particles. The appearance of helium in a tube containing the radium emanation may indicate either that the helium is one of the final