Product Percentage proportion of total activity Radium 25 per cent. Emanation 17 „ Radium A 29 „ Radium B 0 „ Radium C 29 „ The products of radium and their radiation are graphically shown later in Fig. 95. =230. Active deposit of radium of slow transformation.= It has been pointed out (section 183) that a body, exposed in the presence of the radium emanation, does not lose all its activity for a long time after removal; a small residual activity is always observed. The magnitude of this residual activity is dependent not only upon the amount of emanation employed, but also upon the time of exposure of the body in the presence of the emanation. For an exposure of several hours in the presence of the emanation, the residual activity is less than one-millionth of the activity immediately after removal. An account will now be given of some investigations made by the writer[319] on the nature of this residual activity and the chemical properties of the active matter itself. It is first of all necessary to show that the residual activity arises in consequence of a deposit of radio-active matter, and is not due to some action of the intense radiations to which the body made active has been subjected.