upon it. Then a disk is cut out about three quarters of an inch greater in diameter 

 than the original circle. The paper is punctured over the entire surface included 

 within the inner line, and then with scissors little gashes are made from the outer 

 circumference inward, so as to permit of folding the edge of the disk inwardly. A 

 little gum tragacanth, or paste, is then applied to these upturned edges, the disk is 

 then inserted into the jar and pasted securely over the cyanide by means of the up- 

 turned flaps. A jar thus charged will last for a long time if kept stoppered when 

 not in use. Cyanide has a tendency to liquefy in the presence of moisture, and it 

 is well therefore to take care to keep the jar closed when not in use. It must, how- 

 ever, be borne in mind that the fumes of hydrocyanic acid (prussic acid), which 

 are active in producing the death of the insect, will not be given off in sufficient 

 volume unless there is a small amount of moisture in the jar, and in very dry cli- 

 mates the writer has sometimes found it necessary to moisten the bottom of the jar 

 with a drop or two of water. Jars also may be charged with lumps of carbonate 

 of ammonia, but as this substance bleaches the wings of insects, especially those 

 which are green in color, its use is not strongly recommended. Figure 5 on Plate 

 D shows a jar prepared for use. 



When a butterfly has been caught in the net it is apt to flutter about and 

 struggle violently, thus injuring its wings. It is well therefore as soon as the in- 

 sect has been captured to take hold of it at the point where the wings join the body. 



13 



