218 CHROME ALUM AND CHROMIUM CHLORIDE. 
are dark greenish blue, very opaque to the visible 
light-rays, but transparent to the ultra-violet. I used 
a layer 3 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 
” 
9 
2. 
4. 
carbon. 
” 2” 9 
Exp. 3. Most of the ants were under the bisulphide 
of carbon. 
All but three 35 5 
All ” ” 
2 
5. 
I now took chromium chloride instead of alum. 
Exp. 1. 
” 
” 
” 
2. 
Most were under the bisulphide of carbon. 
All 2” 29 od 
. Almost all ’,, Pn 55 
. About three-fourths were under the 
chromium chloride. 
5. All were under the chromium chloride. 
6. About two-thirds ‘3 5 
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 ,, ss ss 
11. All under the chrome alum. 
12. 
3 bisulphide of carbon. 
