Specific Velocities of Ions in the Discharge from Points. 81 



Except in those experiments marked " curves," the " double- 

 position" method was used. 



The hydrogen in the case of Tube A was less pure than 

 that used in Tube B. It was obtained from commercial 

 hydrochloric acid and zinc, and was passed through strong- 

 sulphuric acid and over phosphorus pentoxide. In the other 

 experiments the hydrochloric acid was pure, and the gas was 

 passed through tubes of caustic potash, sulphuric acid,, 

 phosphorus pentoxide, and glass-wool, in that order. In all 

 cases a very slow stream of gas passed through the dis- 

 charge-tube during the experiments at a pressure greater 

 than that of the atmosphere by a few centimetres of water. 



The ring used in Tube A was the brass ring used before 

 with air, cleaned and slightly vaselined on its surface. In 

 Tube B. I, in every table a flat ring of brass, 1 millimetre 

 thick, was embedded in the ebonite so that its inner edge 

 was flush with the inner surface of the tube. By this device 

 the whole pressure of the wind is measured on the pressure- 

 gauge, but against this has to be set the disadvantage that 

 conduction over the inner surface of the tube becomes 

 appreciable for smaller distances between point and ring than 

 in the other arrangement. The ring in experiments II. to 

 V. was an exact copy in platinum of the ring used in Tube A, 

 and was never vaselined. This also applies to all the tables. 



The point was usually of fine platinum wire cut obliquely 

 with scissors to a very sharp end, and sheathed, except a 

 millimetre or two at the end, with glass. In a few of the 

 experiments this was replaced by aluminium, filed sharp, 

 but the change did not cause any certain difference in the 

 results. 



Carbon Dioxide. 



, 



n. 



V+. 



V-. 



V. 



V-/V+ 



~j. 



z. r 





12 



15 



0-76 



0-86 



0-81 



113 



6-0 



20 



Tube A. 



1-6 



11 



0-82 



091 



0-88 



115 



31 



04 



Tube B.I. 



07 



11 



0-81 



0-92 



0-86 



113 



,„ 



, 



,, ,, 



11 



18 



0-85 



0-92 



0-88 



1-08 



62 



3-2 



Tube B. II. 



_. 



113 





0-83 



0-925 



0-88 



Ml... 



Weighted 



means for Tube B only. 



As regards the condition and arrangement of the apparatus 

 and the production of the gas, the same remarks apply here 

 as in the case of the hydrogen table, except that for zinc is 

 to be read marble and for caustic potash water. In II. also 

 the length of phosphorus pentoxide was nearly quadrupled, 



Phil. Mag. S. 6. Vol. 1. No. 1. Jan. 1901. G 



