7 6 SCIENCE PROGRESS 



intensity with that of other spectrum tubes containing known 

 quantities of helium, they actually succeeded in obtaining an 

 approximate measurement of the amount formed. 



Ramsay and Collie, introducing the means already described 

 to free the gas of last traces of carbon dioxide, succeeded in 

 enclosing it in a similar spectrum tube and mapping its spectrum. 

 This is distinct, establishing the emanation as a true element, 

 its general features resemble those of the other gases in the 

 argon series. 



Replacing the spectrum tube by a capillary tube of very fine 

 bore, whose volume measurements were determined subsequently, 

 Ramsay and Soddy made two measurements of the actual amount 

 of emanation produced. They used different capillary tubes and 

 obtained different results in the two cases. In the first experi- 

 ment there was a sudden large drop during the first day, the 

 contraction thereafter being roughly proportional to the decay 

 of activity. The gas completely disappeared by the end of a 

 month. On heating the tube helium was given off from the 

 walls and detected by its spectrum. In the second experiment 

 the initial volume was much smaller. There was no contraction, 

 but the gas expanded during a considerable time. 



An attempt to explain these differences was made some years 

 later by Ramsay and Cameron. On account of the sticktion of 

 the mercury in its passage through the phosphoric anhydride 

 tube they found it convenient to use a somewhat modified 

 apparatus, a sketch of which is shown in fig. 2 (reproduced 

 from the/. Chem. Soc. 1907, 91, 1907, by kind permission of the 

 Secretaries). The whole apparatus was arranged by the side of 

 a scale graduated in millimetres. The general arrangement was 

 the same as that shown in fig. 1. A side tube connected with a 

 second reservoir m was introduced ; the emanation, having been 

 isolated, was allowed to enter through the tap k, which was closed 

 after forcing mercury through it so as completely to clear the 

 tube of gas. The gas was forced up into the capillary tube and 

 its volume read at different pressures (by raising and lowering 

 the reservoir m, and noting the difference in the mercury levels). 

 This was repeated daily for some time. Two glass capillary 

 tubes were used, two sets of measurements being taken with 

 each. Their diameters were respectively 0*448 and 0*453 milli- 

 metres. For the two final measurements a silica tube of 0*208 

 millimetres diameter was taken. Silica and glass cannot be joined 



