THE TRANSFORMATION OF ELEMENTS 75 



the radium solution ; this is known to take place to a slight 

 extent. The excess of hydrogen, however, is extremely useful 

 in enabling the emanation to be separated from admixed gases. 



The test-tube g, containing these gases, is transferred to the 

 mercury trough h, and forced through the inverted syphon, 

 made of capillary tubing, and through the three-way tap into the 

 burette 1. At the top of the burette a little moist potassium 

 hydroxide has been previously melted to the glass ; this absorbs 

 any trace of carbon dioxide. A spark from a coil is passed 

 through the gas by means of the platinum wires at j. Immediate 

 recombination takes place, and only the excess of hydrogen and 

 the emanation remain, but in a moist condition owing to water 

 formed by the explosion. The apparatus above the three-way 

 tap is completely exhausted of air by a second pump, connected 

 through the tap m. This tap is then closed, and the three-way 

 tap opened. The reservoir k is raised and the gas forced 

 through the three-way tap and the small bulb l containing 

 phosphoric anhydride, in order to dry it completely. The 

 mercury is then raised to n, and the three-way tap closed. 

 Liquid air is poured into the cup q; the bulb p cools quickly 

 to — 185 , the emanation condensing within, while hydrogen 

 remains gaseous at this temperature. After about five minutes 

 the tap m is opened, and the hydrogen is completely pumped 

 away. It has been found repeatedly that even at — 185 the 

 emanation has a slight vapour pressure ; pumping must not 

 be carried to excess or else emanation is lost. If the work 

 is carried on in the dark, the pumping is stopped when the 

 bubbles passing down the fall-tube of the pump commence 

 to phosphoresce a little. The tap m is then closed and the 

 mercury level raised to o to prevent leakage through m. 

 During the whole of this time the cup q is kept filled with liquid 

 air. After m is closed, the liquid air is allowed to evaporate, 

 whereupon the emanation regains its gaseous condition and 

 can be examined. 



Using a somewhat similar method, Ramsay and Soddy suc- 

 ceeded in freeing the emanation from most of its impurities and 

 forcing it into a minute spectrum tube such as r in fig. 1, which 

 was then sealed off and examined. They were unsuccessful in 

 obtaining the spectrum of the emanation ; a trace of carbon 

 dioxide masked it. On the other hand, they obtained the spec- 

 trum of helium, which rapidly grew brighter. By comparing its 



