235 



215 



100 



192 



176 



.1119 



237 



225 



105 

 Mean 1'OS 



348 Prof. W. H. Bragg on the Ionization of 



Volts Pressure 



per cm. in cm. Temperature. El. EI (air). Ratio. 



Carbon Dioxide. 



1000 At.rao. 20 



72 

 31 



Nitrous Oxide. 

 1000 Atmo. 29 210 229 1'05 



Oxygen. 

 1000 Almo. 20 247 220 TOO 



Nitrogen. 

 1000 Atmo. 19 211 224 '96 



Of the measurements recorded in the above tables, those 

 for acetylene, ethylene, carbon dioxide, and nitrous oxide were 

 made some time ago. But they are probably quite correct 

 enough to rank with the rest, which have for the most part 

 been made recently, since they are not affected by tempera- 

 ture and initial recombination difficulties. The measurements 

 most likely to contain error are those of the alcohols and 

 methyl iodide, the latter because I have been unable from 

 lack of material to repeat the one somewhat ancient determi- 

 nation, the former because for some reason the alcohols are 

 very difficult to manage in my apparatus. They are apt to 

 cause — particularly methyl alcohol — very large normal leaks, 

 though other vapours, such as benzene, have no such effect. 

 I believe the cause to be connected with the presence of 

 minute particles of fluff, which bridge across the walls of the 

 ionization chamber, being stretched along the lines of force. 

 Although the apparatus is guarded with plugs of glass-wool, 

 yet things of this sort seem to find their way into the chamber 

 at times, and it is possible that the methyl alcohol sets them 

 free from the sides or base of the apparatus to which they 

 are fastened by traces of grease. I have only once had the 

 apparatus in perfect working order with methyl alcohol : at 

 that time I had gone over the working parts with a magni- 

 fying glass to find and remove every foreign particle, and 

 had washed the whole apparatus out with methyl alcohol 

 itself. These good conditions lasted only a short time, and 

 unfortunately a second cleansing process was not equally 

 effective. 



I must point out that the results for benzene and acetylene 

 are now close together. In the preliminary paper I believed 

 them to differ considerably, and used them as an illustration 

 of the want of direct connexion between the energy spent and 



