Page:Radio-activity.djvu/45

 there be shown that polonium, that is, the radio-active constituent mixed with the bismuth, is a distinct chemical substance, which is allied in chemical properties to bismuth, but possesses some distinct analytical properties which allow of a partial separation from it.

The polonium, if obtained in a pure state, should initially be several hundred times as active as pure radium. This activity, however, is not permanent; it decays with the time, falling to half value in about six months.

The absence of any new lines in the spectrum of radio-active bismuth is to be expected, for, even in the most active bismuth prepared, the active matter exists in a very small proportion.

21. The discussion of the nature of polonium was renewed by the discovery of Marckwald that a substance similar to polonium can be separated from pitchblende; the activity of this substance, he stated, did not decay appreciably with the time. The method of separation from the bismuth chloride solution, obtained from uranium residues, was very simple. A rod of bismuth or antimony, dipped in the active solution, rapidly became coated with a black deposit which was intensely active. This process was continued until the whole of the activity was removed from the solution. The active deposit gave out only easily absorbed rays, and in that respect resembled the polonium of Mme Curie.

The active substance was found to consist mainly of tellurium, and for this reason Marckwald gave it the name of radio-tellurium. In later work, however, Marckwald has shown that the active constituent has no connection with tellurium, but can always be separated completely from it by a simple chemical process.

In order to obtain a large amount of the active substance, 2000 kilos. of pitchblende were worked up. This yielded 6 kilos. of bismuth oxychloride, and from this was separated 1·5 grams of radio-tellurium. The tellurium present was precipitated from a hydrochloric acid solution by hydrazine hydrochloride. The precipitated tellurium still showed some activity, but this was removed by repeating the process. The active matter then