Page:Radio-activity.djvu/40

 new radio-active bodies. Although these show distinctive radio-active properties, so far none of them have been purified sufficiently to give a definite spectrum as in the case of radium. One of the most interesting and important of these substances was discovered by Debierne while working up the uranium residues, obtained by M. and Mme Curie from the Austrian government, and was called by him actinium. This active substance is precipitated with the iron group, and appears to be very closely allied in chemical properties to thorium, though it is many thousand times more active. It is very difficult to separate from thorium and the rare earths. Debierne has made use of the following methods for partial separation:

(1) Precipitation in hot solutions, slightly acidulated with hydrochloric acid, by excess of hyposulphite of soda. The active matter is present almost entirely in the precipitate.

(2) Action of hydrofluoric acid upon the hydrates freshly precipitated, and held in suspension in water. The portion dissolved is only slightly active. By this method titanium may be separated.

(3) Precipitation of neutral nitrate solutions by oxygenated water. The precipitate carries down the active body.

(4) Precipitation of insoluble sulphates. If barium sulphate, for example, is precipitated in the solution containing the active body, the barium carries down the active matter. The thorium and actinium are freed from the barium by conversion of the sulphate into the chloride and precipitation by ammonia.

In this way Debierne has obtained a substance comparable in activity with radium. The separation, which is difficult and laborious, has not yet been carried far enough to bring out any new lines in the spectrum.

18. After the initial announcement of the discovery of actinium, several years elapsed before any definite results upon it were published by Debierne. In the meantime, Giesel had independently obtained a radio-active substance from pitchblende which seemed similar in many respects to the actinium of Debierne.