218 CHEOME ALUM AND CHROMIUM CHLORIDE. 



are dark greenish blue, very opaque to the visible 

 iight-rays, but transparent to the ultra-violet. I used 

 a layer inch thick, which was still so dark that I 

 could not see the ants through it ; and for comparison, 

 a solution 1 inch thick of bisulphide of carbon, moving 

 them after each observation as before. 



Exp. 1. The ants were under the bisulphide of 



carbon, 

 o 



>5 J) 55 



Exp. 3. Most of the ants were under the bisulphide 



of carbon. 



4. All but three 



,, 5. All 



I now took chromium chloride instead of alum. 

 Exp. 1. Most were under the bisulphide of carbon. 

 ,, 2. All ,, ,, 



3. Almost all 



4. About three - fourths were under the 



chromium chloride. 



5. All were under the chromium chloride. 

 6. About two-thirds 



7. About one-half under each. 

 8. All under the bisulphide of carbon. 

 9. About three-fourths under the bisulphide 



of carbon. 



10. About half 



11. All under the chromium chloride. 

 12. bisulphide of carbon. 



