58 INFRA-RED TRANSMISSION SPECTRA. 



1.8 n, beyond which the transmission drops rapidly to a minimum at 2.9 [i, 

 previously found. Using this larger dispersion, there appear to be no 

 absorption bands up to 1.9 /*. The study of zinc sulphide is of interest in 

 connection with luminescence of one form of this substance known as 

 Sidot blende. In their study of the rapidity of decay of phosphorescence 

 in Sidot blende, when subjected to infra-red rays, Nichols and Merritt 1 

 found that the rate of decay was the most rapid when exposed to infra-red 

 rays of wave-length 0.9 n and of wave-length 1.37 [i. From this it would 

 seem that the screen of Sidot blende possessed broad absorption bands 

 with maxima in the region of 0.9 p. and 1.37 ll. The luminescence of 

 Sidot blende appears to be due to some metal dissolved in it. From the 

 foregoing experiment on sphalerite (ZnS) it appears that these absorption 

 bands are not due to the ZnS, but rather are to be sought for in the dis- 

 solved metal (see cobalt glass) , and in the cement, in case a glue is used to 

 secure the powder in the form of a " screen." The present study of colored 

 glasses gives us some idea of what to expect in solutions of metals (oxides 

 of metals?) in glasses; while the phenomenon maybe further complicated 

 by the molecular structure of ZnS, which in the form of Sidot blende 

 may have absorption bands not found in sphalerite. 



1 E. L. Nichols and E. Merritt: Phys. Rev., 25, p. 362, 1907. 



