306 SxMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. $2 



Zinc oxide. 



1. When prepared by burning thoroughly in O2, it showed an intense 



green fluorescence: W6(S9o) ; Tfi(6i3); 84(649). 

 Oxide became cofifee-colored and sticky: Tf 1(614). 

 Oxide permanently discolored yellow during fluorescence : 



W6(590) ; W7. 

 White color and power to fluoresce restored by heating: Tf 1(616). 

 Oxygen is released during the fluorescence: W6(59o) ; Tfi(6l3). 

 No chemical change occurs large enough to detect by balance: 



Tfi(6i4). 

 Oxide can be discolored and power to fluoresce be removed by 



intense pressure: Tf 1(615). 



2. Chemically precipitated oxide shows little or no fluorescence : 



W6(S90); Tfi(6i6). 

 Oxide may be purified chemically until it will no longer fluoresce : 



Sm3(623, 628). 

 Minute traces of cadmium oxide caused it to show an intense 



green fluorescence: Sm3(628). 

 Flakes or smoke from burned Zn show no fluorescence unless 

 heated: 83(390). 

 Explanation offered is that pure ZnO does not fluoresce except when 

 it contains some other oxide in solid solution : 

 8m3(623, 628); cf. Tf2. 

 Metallic Oxides in General. 



Pure oxides, chemically obtained, do not fluoresce: Sm2(707) ; 



8m3(62S, 628, 633); Ew3(303). 

 Oxides obtained by burning the metal may fluoresce: Ew3(303). 

 Oxides containing other oxides in solid solution may fluoresce: Sm2(707) ; 



8m3(625, 628, 633). 

 Fluorescence the same in either H- or O2: Ew3(303). 

 Fluorescence in General. 84(649). 



Temporary. All substances soon lose capacity to fluoresce in canal rays : 



Ari(326); 8m2(7o6) ; W6(59o) ; W7. 

 Extremely sensitive to minute quantities of impurity: Sm2(7io). 

 Superficial: Ari(326); Sm2(7o6). 



Spectrum. As fluorescence dies down spectrum bands widen out and 

 finally disappear in a continuous spectrum : 8m2(707, 711 'i. 



5. CHARGE CARRIED BY THE RAYS. 



Rays Positively Charged for the most part. 



Shown by the direction of the magnetic and electrostatic deflection (see 



below): Tmi(52i); 8m4(iio). 

 Shown by the positive charge received by a Faraday cylinder or electrode 



struck by the rays, cathode being earthed : Prni ; 



Wi; W3(446); Ewi(i7S) ; Bgi(692); W5(524, 251); 



Ln2(i98); W9(67i) ; Aui ; Fi(i53); Pryi. 

 Note. — In order to give the true current carried by the rays, charge 



received by an electrode must be corrected for two 



secondary effects elsewhere described, viz : 



