218 CHEOME ALUM AND CHROMIUM CHLORIDE. 



are daxk greenish blue, very opaque to the visible 

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

 a layer ^ inch thick, which was still so dark that 1 

 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. 



JJ '^' 55 »5 5? 



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

 of carbon. 

 „ 4. All but three „ „ 



„ 0. 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. 



