REPORT OF THE SOCIETY • 71 



Chemical Substances Used. 



The more useful chemical substances that have given promising results when 

 applied for the purpose of killing weeds are as follows: — Sulphuric acid, iron sul- 

 phate, copper sulphate, common salt, caustic soda, sodium arsenite, carbolic 

 acid, orchard heating oil, and fuel oil. 



Sulphuric acid or oil of vitriol. Owing to its corrosive effect on the spraying 

 apparatus this chemical can only be used in a fairly weak solution. The propor- 

 tions vary from 3 to 10 per cent of acid and the spray is applied at the rate of 60 

 to 134 gallons per acre. It has no injurious action on wheat, oats, or barley crops. 

 It should be applied when the weed has from 3 to 5 leaves. The solution is 

 effective 3 or 4 hours after application and has a fertilizing effect on the soil. 



Iron Sulphate or Copperas or Green Vitriol. — A solution varying in strength 

 from 15 to 20 per cent is usually employed; this strength may be obtained by 

 dissolving 100 pounds of the sulphate in 52 gallons of water, which quantity is 

 sufficient to spray one acre. It has no injurious effect on grain crops or grasses or 

 peas but cannot safely be employed with a bean crop. A 20% solution is too strong 

 to use in a field of flax, considerable injury resulting when that strength is applied 

 to flax 5 inches high. Grain crops should always be sprayed before the plants 

 have "headed" or come into ear. 



Copper Sulphate or Bluestone or Blue Vitriol. — ^This may be used wherever 

 iron sulphate is recommended but in a much weaker solution. From 8 to 12 pounds 

 of copper sulphate are used to 52 gallons of water; 50 to 75 gallons of the solution 

 are applied per acre. 



Common Salt or Sodium Chloride. — ^This is one of the easiest and safest 

 sprays to use. A 20% solution is generally employed; 150 pounds to 60 gallons 

 of water will spray one acre. The chief drawback to the too frequent use of this 

 chemical is that, it may permeate the soil to such an extent as to check the growth 

 of other plants before it is finally washed out by rain. 



Caustic Soda or Sodium Hydrate. — A 5% solution (2 pounds in 4 gallons of 

 water) is employed but as this chemical is likely to kill all other vegetation it 

 can only be used on waste ground or on ground that is not intended to be used until 

 the chemical has been washed out of the soil. 



Sodium Arsenite. — ^This is used at the rate of 1^ to 2 pounds in 52 gallons 

 of water per acre. It is very poisonous and great care is necessary in its use; the 

 powder is dangerous to health if inhaled. 



Carbolic Acid is used chiefly for the destruction of plants growing on waste 

 ground, the strength of solution employed varying from 12^% upwards. 



