CHEMICAL HERBICIDES 15 
no effect and require that it be done over again. It is necessary 
that sprays shall be fine, like a fog or a mist, in order to be effectual ; 
for drops only roll off the leaves as rain would do, and small drops 
merely make large ones. 
Carbolic acid (Phenol). This can be used only on small areas 
because of its cost. The crude acid may be used in full strength to 
saturate the soil about the perennial roots of such plants as Milk- 
weed and Canada Thistle. It does not corrode metals and can be 
used with any sort of can or pump. When diluted with water it 
needs to be constantly shaken in order to make a good mixture. 
It is quick in action, but not lasting. The treated plants, if deeply 
rooted, often recover and send up new shoots. 
Caustic soda (Sodium hydrate, or Sodium hydroxide). To be 
used where one does not mind killing out all plant growth for a 
season. Better than Carbolic acid for killing Poison Ivy, Spread- 
ing Dogbane, or any other woody and deep-rooted plants. Apply 
in strong solution, preferably in hot, dry weather, and, when the 
noxious growth is killed, water the bare spots frequently so as to 
assist the chemical to leach away. 
Oil of vitriol (Sulfurte acid). This can be handled only in glass 
vessels. It is not used as a spray, but is applied directly to indi- 
vidual plants that are particularly hardy and pernicious. Very 
great care is necessary in its use, as it destroys everything that it 
touches; if accidentally spilled it may make painful “burns” on 
the flesh or eat holes in clothing. It is not recommended, as other 
chemicals are very nearly as effective and are very much less 
dangerous to handle. 
Corrosive sublimate (Bichloride of mercury). Make a solution 
in proportions of one ounce of the drug to six gallons of water. 
Though fatal to the weeds, this, too, is not to be recommended for 
any general use because of its extremely poisonous nature. Its 
cost is also much greater than less dangerous chemicals. 
Kerosene. Crude petroleum. Either of these will kill plants, 
and the former is usually always at hand in the farm household. 
They have the merit of being safe to handle, but are relatively 
more costly than other herbicides. The saturated soil remains 
sterile longer than with applications of caustic soda or carbolic acid. 
Arsenite of soda. This is a very active poison, and extreme care 
