INFINITESIMAL QUANTITIES RAMSAY. 



221 



the vessel in a solid state. Consequently, we can easily separate tlie 

 two, removino; the liydrogen with the pump. The emanation then 

 remains entirely j^ure. 



I shall begin by giving jou an idea as to how we set about meas- 

 uring the volume of the emanation. In the first place, one nmst avoid 

 all contact between the emanation and the grease of the pump-tap, 

 for fear that the resulting carbonic acid ma}^ make the gas impure. 

 We avoid all danger of this kind by seaUng the explosion-tube with 

 mercury; but in order to guard against this contamination, we leave 

 the hydrogen with the emanation for tliree hours in a small tube 

 whose upper part contains some caustic potash melted upon the walls. 

 This period having ela})scd, the products of the disintegration of the 

 emanation have reached their maximum, for ra- 

 diums A, B, and C have but a short life, changing 

 into D, which is without radio-activity. It being 

 necessary, for reasons which will appear later on, 

 to measure the j- rays at this j uncture, with the 

 aid of an electroscope we determine the emana- 

 tion's power of discharge. 



In figure 1 we see the small tube a. We see also 

 a reversed siphon closed by a kind of glass cap. 

 The cap being raised and the tube placed above, 

 the gases enter the apparatus through the capil- 

 lary tube h, narrow at the upper end, to prevent 

 the mercury from entering too rapidly. 



But before introducing the gas it is necessary 

 to ernpty the apparatus. Opening the tap and 

 lowering the reservoir / we connect the pump 

 with the apparatus. We remove all air and by 

 means of the reversed siphon admit some hydro- 

 gen, which must remain for a night in the appa- 

 ratus in order to displace atmospheric air adher- 

 ing to the walls. This displacement is accelerated by heating in the 

 flame the tubes 1c, i, j, I, m. In the morning the apparatus is again 

 pumped empty. The reservoir/ is raised in order to make the mercury 

 ascend above the tap h, and the tap is shut. At noon the measurements 

 of radioactivity will have been made, and we introduce the hydrogen 

 with the emanation, replacing the cap, which, sealed with mercury, 

 has no need of grease to make the joint air-tight. The gases can not 

 come into contact with the tap, which is protected by the mercury. 



You can see a tube i containing some pieces of caustic baryta. 

 This arrangement is for two purposes: First, to dr}^ the gas; secondly, 

 to remove ever}^ trace of carbonic acid wliich may have escaped the 

 action of the potash. The gas is left in the tube for half an hour to 

 make sure that neither moisture nor carbonic acid remain. 



FiG.l. 



