Another method of obtaining the same result is to dissolve crystallized uranium nitrate in ether. Two layers of solution are formed, one ether and the other water coming from the water of crystallization. The aqueous layer is active, while the water layer is inactive. Similarly, by adding barium chloride solution to a solution of a salt of uranium and then precipitating the barium as sulphate, the activity is transferred to this precipitate. These experiments give proof of the formation and separation of a radio-active body by ordinary chemical operations. So, too, in the case of thorium salts a substance can be obtained by means of ammonium hydroxide which is several thousand times more active than an equal weight of the original salt. After standing a month, the separated material has lost its activity and the thorium salt has regained it. Here, again, there is the formation, separation, and loss of a radio-active body. Conclusions Drawn Now, these are ordinary chemical processes for the separation of distinct chemical individuals. The results, therefore, lead naturally to the conclusions: (1) it would seem that uranium and thorium are themselves inactive and the activity is due to some other substance formed by these elements; (2) this active substance is produced by some transformation in those elements, for on standing the activity is regained. This latter conclusion is startling, for it indicates a change in the atom which, up to the time of this discovery, was deemed unchangeable under the influence of such physical and chemical changes as were known to us. Search for New Radio-active Bodies The search for new radio-active bodies and the study of their characteristics has been systematically and successfully carried on. The bodies obtained in the above experiments were named uranium _X_ and thorium _X_, respectively. Further, it became clear from the investigation of uranium minerals that radium, polonium, actinium, and ionium originated from uranium. From thorium minerals a body was separated called mesothorium, which was analogous to radium. Both thorium and radium were found to give off a radio-active gas. The first lost half of its activity in less than one minute. The second was more stable and lost half of its activity in about four days. The name radium emanation was given to the latter and it was found chemically and physically to belong to the class of monatomic or noble gases, such as helium, argon, neon, etc., which had been discovered by Ramsay. In some cases the chemical action was determined and these new bodies were found analogous to well-known elements, as radium to barium, polonium to bismuth. The physical properties were investigated and, where possible, spectra were mapped and atomic weights determined.