6 Baker, hifluence of Moisture on CJicniical Change in Gases. 



containing the glass. Finally about 2 mg. of radium 

 bromide was heated in the mixture of gases. As soon as 

 the combining temperature was reached, the gases in the 

 radium bromide tube exploded. 



From these three experiments it is seen that as the 

 amount of ionization was increased, there was a rapid 

 increase in chemical action. 



The next experiment tried, illustrates one way in 

 which the ionization of a gas may bring about chemical 

 change. 



Hydrogen sulphide and sulphur dioxide can be 

 mixed at the ordinary temperature in presence of traces of 

 moisture, but in presence of liquid water, decomposition 

 takes place into sulphur and water. The gases were dried 

 before mixing by calcium chloride, which leaves about 

 4 mg. of water vapour per litre in the gas. After mixing, 

 a small open silica tube containing about 2 mg. of dried 

 radium bromide was introduced. After six hours no 

 apparent change had taken place in the gas ; there was no 

 deposit of sulphur on the sides of the jar, and it seemed at 

 first as if no action had been produced. On opening the 

 jar, however, an inrush of air was noticed, and the contents 

 were almost odourless. On heating the radium tube a 

 large quantity of water was driven off, and a copious 

 sublimate of sulphur was seen. The whole of the gaseous 

 contents of the jar had condensed in the small tube con- 

 taining the radium bromide. The explanation of this 

 action of radium bromide is probably simi^le. Water 

 vapour condenses on the ions emitted, liquid drops are 

 formed, and in them the chemical action takes place.* 



* I have invariably noticed ihal water collects in lubes containing radium 

 preparations exposed to undried air. The salts are not at all deliquescent^ 

 the crystals appearing quite sharp-edged under the microscope. 1 found 

 that lo mg. of radium bromide exposed to an atmosphere saturated at o" 

 for two days caused a deposition of water on its surface weighing 15 mg. 



