156 



to secure pure sulphate of copper, as in commerce it 

 frequently contains impurities. Sulphate of copper is 

 now worth ,17 per ton in London. Sulphate of iron 

 is a common adulterant, and may be detected when 

 making the solution, because instead of the mixture 

 assuming a blue hue, it turns brown. Ground sulphate 

 of copper dissolves more readily than that in blocks. 

 It is necessary that thoroughly fresh-burned lime of good 

 quality be procured. If not, the caustic properties of 

 the copper will not be neutralised, and there will be an 

 undue amount of sediment, which will prove trouble- 

 some when working. 



Requirements when Spraying. 



Several vessels are required in the field. The water- 

 cart to bring water to the field. A large tub or two 

 if water has to be fetched a long distance. Three 

 tubs, each sufficiently large to prepare as much of the 

 solution as the barrel of the machine will hold. Thus, 

 for a 60-gallon machine, 70-galloii tubs are required; 

 and for a 40-gallon machine 45 to 50 gallons. In 

 addition to these, several wooden buckets, marked so 

 as to indicate the gallons, are required. All vessels 

 used in mixing should be of wood, as the copper 

 rapidly affects metals. It is convenient to have a 

 boiler to heat water to dissolve the sulphate of copper, 

 though this is not absolutely necessary if the work is 

 proceeded with systematically, or if the solution of 

 copper is made previously. When the latter is done 

 the specific gravity of the copper solution must be 



