1911-12.] 
Experiments in Radioactivity. 
393 
XXVII.— Experiments in Radioactivity ; the Production of the 
Thorium Emanation and its Use in Therapeutics : Thorium 
X. By Dr Dawson Turner. 
(Read June 3, 1912. MS. received June 14, 1912.) 
The thorium emanation is given off more or less freely from the compounds 
of thorium, the best source, according to Professor Soddy, being a prepara- 
tion of radiothorium in a moist condition. The important members of this 
group from the medical point of view are mesothorium, thorium X and its 
emanation. 
The presence of the emanation can by shown by the ionising effect in 
discharging an electroscope, by the phosphorescence it imparts to zinc sul- 
phide, and by its behaviour as a gas. The ionising effect can be produced 
at a considerable distance, and in consequence after a certain lapse of time. 
At a distance of ten feet there is a delay of about half a minute before the 
leaves begin to fall; when once the fall has begun, it continues steadily 
until the leaves are discharged. Experiments were performed to ascertain 
whether the presence of an electrified wire gauze screen placed between the 
source of the emanation and the electroscope would produce any recognis- 
able effect. At first it appeared that when the screen was negatively 
electrified the rate of discharge was accelerated and vice versa, the rate of 
discharge being three seconds when the screen was negatively electrified, 
five seconds when unelectrified, and ten when positively electrified. On 
surrounding the electroscope with an earthed conductor this difference 
disappeared, so that the effects previously observed must have had an 
electrostatic origin. A powerful magnetic field interposed between the 
source of the emanation and the electroscope was also found to produce no 
recognisable effect. 
There are various methods of preparing the active thorium compounds 
for therapeutic use. 
1. By inhalation. In this case the medicament would enter the body 
by the lungs. 
2. By ingestion. 
3. By baths containing a solution of thorium X. It is found in bath 
treatment that considerable quantities of the active substance enter the 
body by inhalation as well as through the skin. 
