=209. Radiations from Thorium products.= It has been shown in the last section that the activity of thorium, by successive precipitations with ammonia, is reduced to a limiting value of almost 25 per cent. of the initial activity. This “non-separable activity” consists of α rays, the β and γ rays being altogether absent. According to the disintegration theory, this is an expression of the fact that the initial break-up of the thorium atom is accompanied only by the expulsion of α particles. We have seen in section 156 that the thorium emanation also gives out only α rays. In the active deposit, thorium A gives out no rays, while thorium B emits all three types of rays. Some hours after separation, Th X gives out α, β, and γ rays, but the appearance of β and γ rays is probably due to the thorium B associated with it. The β and γ ray activity of Th X is much reduced if a current of air is continuously aspirated through a solution of Th X to remove the emanation. It seems likely that if the emanation could be removed as fast as it was formed, so as to prevent the formation of thorium B in its mass, Th X itself would give out only α rays: but, on account of the rapid rate of change of the thorium emanation, it is difficult to realize this experimentally. =210. Transformation products of Thorium.= The transformation products of thorium and the rays emitted by them are graphically shown below (Fig. 81). [Illustration: Fig. 81.] A table of the transformation products of thorium is shown below, with some of their physical and chemical properties. Product Time to be λ (sec)⁻¹ Radiations Physical and half chemical transformed properties Thorium α rays Insoluble in ammonia Th. X 4 days 2·00 × α rays Soluble in 10⁻⁶ ammonia Emanation 54 secs. 1·28 × α rays Inert gas, 10⁻² condenses −120° C.