In the above separations use was made of relationships to bismuth and barium. Similarly, by taking advantage of chemical relationship to the iron group of elements, another body was partially separated by Debierne, to which he gave the name actinium. Boltwood discovered in uranium minerals the presence of a body which he named ionium, and which is so similar to thorium that it cannot be separated from it. It, however, far exceeds thorium in activity.
The lead which is present in uranium and thorium minerals—apparently in fairly definite ratio to the amount of uranium and thorium—is found, on separation and purification, to possess radio-active properties. This activity is due to the presence of a very small proportion of an active constituent called radio-lead, which has chemical properties identical with those of ordinary lead. The bulk of the lead obtained from radio-active minerals differs in atomic weight from ordinary lead and appears also to be different according to whether its source is a thorium or a uranium mineral.
A large number of other radio-active substances have been separated and some of their properties determined, but these were found by different means and will be noted in their proper place. They number in all more than thirty. The sources or parents of these are the original uranium or thorium, and the products form regular series with distinctive properties for each member.
CHAPTER II
PROPERTIES OF THE RADIATIONS
The activity of these radio-active bodies consists in the emission of certain radiations which may be separated into rays and studied through the phenomena which they cause.
Ionization of Gases
One of these phenomena is the power of forming ions or carriers of electricity by the passage of the rays through a gas, thus ionizing the gas. The details of an experiment will serve to make the meaning of this ionization clear.