216 CHEMISTRY OF FARM PRACTICE 



Carbon bisulphide (082) when partially decomposed by 

 standing is a vile-smelling liquid which vaporizes at ordinary 

 temperatures. Its use in the field is limited, being mainly 

 confined to the control of certain root-infesting plant lice. 

 It is extensively used for the control of insects in granaries. 

 In tight cribs it is best applied on top of grain or corn at 

 the rate of 6 pounds to 100 bushels applied when the tem- 

 perature is above 65 F. 



Hydrocyanic acid gas (HCN) is prepared by treating 

 potassium cyanide with excess of sulphuric acid; 2KCN 

 +H2SO4 = 2HCN+K2SO4. This gas is very poisonous 

 and its use is not advised. When used, the proportion of 

 1 pound of the potassium cyanide, 2 pounds of sulphuric acid 

 and 4 pounds of water gives a rapid evolution of the gas. 

 Care must be exercised not to inhale the extremely poisonous 

 fumes. 



163. Fungicides. Bordeaux mixture is prepared from 

 copper sulphate (CuSO-j) and calcium hydrate (Ca(OH)2). 

 The most common proportions are 4 pounds of copper sul- 

 phate and 4 pounds of quicklime to 50 gallons of water. 

 The copper sulphate should be dissolved and made up to 

 25 gallons of water. The lime should be carefully slaked 

 with water and made to twenty-five gallons. Pour the 

 dilute solutions into the spray barrel, stirring vigorously 

 and use while fresh. The above proportions may be widely 

 varied to meet special needs. 



Copper sulphate is difficult to dissolve. The solution 

 may best be accomplished by putting the powdered crystals 

 in a small bag which is suspended over night in the water, 

 near the surface. The copper sulphate solution, being more 

 dense than water, sinks, leaving the copper sulphate crystals 

 in constant contact with an unsaturated solution. Powdered 

 portions of the crystals will dissolve rapidly in hot water. 



Lime-sulphur has already been discussed. As a fungicide 

 for plants in foliage, the commercial product, 32 Baum6, is 

 applied at the rate of 1 to 2 gallons in 50 gallons of water, 



