16 A MANUAL OF WEEDS 
must be exercised in its use. Do not inhale the powdered drug 
when making the solution, or the spray as it is delivered; keep to 
the windward side while working with it. The formula for the 
_ solution is one pound of the drug in three to nine gallons of water. 
White arsenic is cheaper than Arsenite of soda, but needs to be 
combined with twice its weight of Sal soda in order to be readily 
soluble in water; the formula being, one pound of White arsenic, 
two pounds of Sal soda, three to nine gallons of water. These 
arsenical compounds are the chief ingredients of all commercial 
weed-killers, and are used on walks, roadways, tennis courts, and all 
places, where the complete and lasting extirpation of all plant 
growth is required. 
