CHAPTER V. 



SIMULTANEOUS ELECTRIC AND VOLUMETRIC GRADUATION OF THE COLOR TUBE. 



1. The lyrohUm stated. — After graduating the color tube in terms of the volume 

 inilux })er second of air saturated with phosphorus emanation, it is next necessary 

 to investigate corresponding data for the degree of ionization of air as related to 

 the color effect. Indeed both graduations may be made simultaneously by passing 

 a known volume of saturated air per second through a suitably constructed tul)ular 

 condenser, and observing coincident values of the electrical leakage of the latter 

 and the color of the enclosed steam jet. Clearly the colors of the tube will each 

 correspond to a definite electrical curient passing through the condenser. More- 

 over, while the volumetric equivalent of a given color is dependent on the degree 

 of saturation of the phosphorus emanation conveyed by the current of air, the 

 electric equivalent should be independent of it. The final graduation cannot at 

 once be carried out, however; for in the case of the color tube constructed and used 

 as below, the nuclei are injected into the air current maintained by the steam jet. 

 An arbitraiy element is thus introduced, and the results will only be comparable 

 when all observations refer to a tube the action of which has been left quite undis- 

 turbed. True, thei'e seems to be no objection to putting a vane anemometer into 

 the influx pipe (enlarged) of the color tube, in which case the arbitiary factor 

 would be specified ; and othei' methods of eliminating the factor will be indicated, 

 but the data following refer to the earlier methods of experiment. 



2. Apparatus.— In figure 1, CC' is the color tube, with the jet j, the ther- 

 mometer T, and the influx pipe C", bent for convenience. KL is the tubular con- 

 denser, consisting as shown in detail in figure 2, of a brass tube (/, .6 centira. in 

 internal diameter and effectively 50 ceutims. long, surrounding a steel rod a, .318 

 centim. in diameter, coaxially. Rod and tube are separated symmetrically through- 

 out by the short hard-rul)ber tubes, I, at each end, fitting over the rod and within 

 the tube, snugly. Thus the cylindiical shell (air space) is but .141 centim. thick 

 and 50 centim. long, and the condenser is adapted to bring to bear a high potential 

 gi-adient (the shell of aii' being as thin as admissible in consideration of flexure) 

 along a considei'able length of air column conveying phosphorus nuclei. The out- 

 side of the condenser (figure 1) is permanently put to earth, while the rod inside is 

 in metallic connection with the electrometer needle, as suggested in the figure at E. 

 A suitable key is added (see figure 1, Chapter IV., at S 1) in order to conveniently 

 charge the rod. Upwards of 300 volts were applied. Notwithstanding its slender 

 dimensions, no difficulty attended the use of the condenser. 



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