CONSTRUCTION OF VENTILATORS AND FLOORS 117 



the cyanide dropped in. The trap-door is closed 

 quickly and is covered immediately with a piece of 

 cloth (blanket is best), and dirt hurriedly thrown 

 over the whole business. This prevents any of the 

 gas from escaping, and makes the building absolutely 

 air-tight, which is necessary. The gas fills the exca- 

 vation and rises through the loose floor, permeating 

 through the trees, filling the entire inside of the 

 house. In our building we treat about five thousand 

 trees at a time. For fall deliveries we treat the stock 

 as it comes from the field to the packing-ground. For 

 spring delivery we treat them as we take them from 

 the healing grounds to the packing-grounds. The 

 cost of our building did not exceed $50 complete. ' ' 



