studies of phosphorescence; of SHORT DURATION. I I I 



than i per cent) of MnS0 4 , dissolved in water, was added to the ZnCl 2 

 solution and the whole brought to the boiling point. An equal volume of 

 sodium silicate, as the flux, was then added and the whole evaporated to 

 dryness. On being exposed to the spark, faint green phosphorescence 

 could be seen. It was then placed in a porcelain crucible and heated to a 

 bright red for 2 hours. When cool it showed pale green fluorescence when 

 exposed to the spark, and when the exciting source was cut off it was found 

 to have considerable bright green phosphorescence. A sample of the 

 powder at this point was kept and marked ZnCl 2 No. 1. The remainder 

 of the powder was heated to a bright red for 3 hours and when cool showed 

 both fluorescence and phosphorescence of greater intensity than did ZnCl 2 

 No. 1. A sample of this was saved and marked No. 2. The remaining 

 powder was heated 2 hours at a bright red; on examination when cool it 

 was found to have lost some of its original phosphorescent intensity. This 

 was marked ZnCl2 No. 3. 



CdCk+xMnSOi Substituting CdCl 2 for ZnCl 2 , but giving it exactly 

 the same treatment, it was found that it was necessary to heat the compound 

 at a bright red for 3 hours before the phosphorescence was very intense, and 

 that subsequent heating had no marked effect on its phosphorescent in- 

 tensity when exposed to the spark. The fluorescence was pink and the 

 phosphorescence dark red. 



CdSOi + xMnSOi. Some CdS0 4 was dissolved in water with a small 

 trace of MnS0 4 and the whole heated to dryness without adding the flux. 

 The resulting white powder showed pale yellow fluorescence, and an orange 

 yellow phosphorescence of much longer duration than the zinc compounds. 



ZnSOi + xMnSOi. ZnS0 4 substituted for CdS0 4 and treated in the 

 same way resulted in a white powder which showed pink fluorescence and 

 bright red phosphorescence, but the intensity was too small to be measured 

 by the method used. 



Some "chemically pure" calcium sulphide was purchased with the view 

 of trying to prepare compounds of CaS and MnS0 4 , but it was found to be 

 already an active phosphorescent compound having a brownish-red color. 



Two large pieces of willemite, showing brilliant green phosphorescence 

 with the iron spark, were studied. It was found that their rates of decay 

 were not the same. The sample having the slowest decay was marked 

 willemite No. 5. The sample having the very rapid decay was crushed 

 into a line powder, a sample made into a screen and marked willemite No. 1 . 

 Part of the powder was heated to a bright red heat in a porcelain crucible for 

 45 minutes. This was marked willemite No. 2. The remainder of the 

 powder was heated for 2 hours at a bright red, and marked willemite No. 3. 



One ZnCl 2 -f-.vMnS0 4 sample made by W. S. Andrews, Schenectady, 

 N. Y., was also studied. 



For purposes of study, screens were made by placing the phosphorescent 

 powder on small squares of heavy dark brown cardboard, the cards having 

 been covered first with white "zapon" varnish. 



Among the preparations just described was one of cadmium sulphate 

 and manganese sulphate made by simply evaporating to dryness a water 

 solution of the two salts. After studying this compound it was put aside 

 for several months and when taken up later for further work it had lost 



