hours, their initial activities in the solid state were 460 for the not heated portion and 420 for the heated one; the difference between the two portions was therefore not considerable. But if the two products do not remain for a sufficient length of time in solution—if, for example, they are evaporated to dryness, immediately after solution—the not heated product is much more active than the heated one; a certain time is necessary in the dissolved state for the effects of heating to disappear. A product of activity 3200 was heated, and its activity thereby reduced to 1030. This product and a similar portion which had not been heated were simultaneously dissolved, and the two then immediately evaporated to dryness. The initial activity was 1450 for the not heated portion, and 760 for the heated one.
Fig. 13.
In the case of solid radium salts the capacity for exciting induced radio-activity is largely affected by heating. During heating radium compounds give off a larger amount of emanation than at the ordinary temperature; but on being cooled to the ordinary temperature, not only is their radio-activity much less than before heating, but their capacity for inducing activity is much diminished. During the time that follows the heating, the radio-activity of the product increases, and may even exceed the original value. The induction capacity is also partially re-established; however, after prolonged heating to redness, this capacity is almost entirely destroyed without spontaneous re-appearance afterwards. The induction capacity may be restored to the radium salt by dissolving it in water, and drying it in the oven at a temperature of 120°. This seems to have the
