EXPERIJWENTS WITH IONIZED AIR. 15 



used to test the persistence of X-ray dust in the pipes D. The I'esidts are as 

 follows, the time of transfer being found by the phosphorus pellicle. 



The Jet being of the usual pattern, it will be seen that dust due to phosphorus 

 and to the X-rays is about equally persistent, being supposedly of the same nature 

 in both instances, namely, ionized aii'. The dusting activity of phosphorus is here 

 far stronger, however, as the colors show. 



19. Differential experiments with long tubes. — A few tests with the differ- 

 ential appai-atus, figures 2 and 4, may here be referred to, the connecting pipe, ]), 

 being about 50 feet long. If the near tube, (I) or A, is opaque (steam at high 

 pressure), the far tul)e, (11) or A', shows a gray field not quite opaque. The dust 

 producer (P), active in (I), will not be so in (II). If the latter be supplied with its 

 own jet, phosphorus will again color the field. If the tube length is 34 feet the 

 result is not materially changed. For 14 feet of tube length both become opaque, 

 but no color is seen in (II), only a less degree of darkness. For 5 feet of tube 

 length, the colors are the same in both apparatus, but muddy and dull in the 

 second. Yellow brown in (I) becomes opaque in (II). No congested tube will 

 produce the yellows of the first order, nor any colors brilliantly. The distribution 

 of particles has become irregular as to size. A stimulated draft would be needed. 



20. Ultraviolet ionizers. — Results with ultraviolet light failed in all instances 

 except with the wide vessel, which was not tried. Sparks of a Holtz machine 

 screened by a quartz window showed no darkening of the tube, wherever applied. 

 The sparking apparatus is given in figure 21, the terminals being of zinc and the 

 window, a, of cj^uartz. 



