Since the uranium is thus continuously radiating energy from itself, w — Radio-activity

"Mme Curie has utilized the coloration of the crystals of radiferous barium as a means of controlling the final process of purification. The crystals of salts of radium and barium deposited from acid solutions are indistinguishable. The crystals of radiferous barium are at first colorless, but in the course of a few hours, become yellow, passing to orange and sometimes to a beautiful rose color. The rapidity of this coloration depends on the amount of barium present. Pure radium crystals do not color, or at any rate not as rapidly as those containing barium. The coloration is a maximum for a definite proportion of radium, and this fact can be utilized as a means of testing the amount of barium present. When the crystals are dissolved in water the coloration disappears."

"Both polonium and radium exist in infinitesimal quantities in pitchblende. In order to obtain a few decigrammes of very active radium, it is necessary to use several tons of pitchblende, or the residues obtained from the treatment of uranium minerals. ...M. and Mme Curie were indebted for their first working material to the Austrian government, who generously presented them with a ton of the treated residue of uranium materials, from the State manufactory."

"Since the preliminary announcement of the discovery of radium, Giese has devoted a great deal of attention to the separation of radium, polonium, and other active bodies from pitchblende. ...Using the method of fractional crystallization of the bromide instead of the chloride he has been able to prepare considerable quantities of pure radium. By this means the labor of final purification of radium has been much reduced. He states that six or eight crystallizations with the bromide are sufficient to almost completely free the radium from the barium."

"The polonium prepared by Mme Curie differs from the other radio-active bodies in several particulars. In the first place the radiations include only very easily absorbable rays. The two penetrating types of radiation given out by uranium, thorium, and radium are absent. In the second place the activity does not remain constant, but diminishes continuously with the time. Mme Curie found that the polonium lost half its original activity in the course of eleven months."

"Mme Curie has made successive determinations of the atomic weight of the new element with specimens of steadily increasing purity. ...In these experiments about 0.l gram of pure radium chloride has been obtained by successive fractionations. The difficulty involved in preparing a quantity of pure radium chloride large enough to test the atomic weight may be gauged from the fact that only a few centigrams of fairly pure radium, or a few decigrams of less concentrated material, are obtained from treatment of about 2 tons of the mineral from which it is derived. ...Runge and Precht have examined the spectrum of radium in a magnetic field, and have shown the existence of series analogous to those observed for calcium, barium, and strontium. These series are connected with the atomic weights of the elements in question, and Runge and Precht have calculated by these means that the atomic weight of radium should be 258--a number considerably greater than the number 225 obtained by Mme Curie by means of chemical analysis. Marshall Watts, on the other hand, using another relation between the lines of the spectrum, deduced the value obtained by Mme Curie. Considering that the number found by Mme Curie agrees with that required by the periodic system, it is advisable in the present state of our knowledge to accept the experimental number rather than the one deduced by Runge and Precht from spectroscopic evidence."

"Radium is extracted from pitchblende by the same process necessary to separate barium, to which it is very closely allied in chemical properties. ...The chloride of radium is less soluble than that of barium and can be separated from it by the method of fractional crystallization."