26 FUNGOID DISEASES 



copper per ten million. The exact composition is 

 unknown, for it varies according to the manner of 

 preparation, the degree of purity of the lime, and the 

 copper used. When freshly prepared it consists 

 essentially of a saturated watery solution of calcium 

 sulphate and calcium hydroxide, containing in sus- 

 pension calcium sulphate and copper hydroxide and 

 a varying amount of calcium hydroxide and calcium 

 carbonate. When exposed to the air the calcium 

 hydroxide takes up carbon dioxide, forming calcium 

 carbonate which is washed away by subsequent 

 rains . Whether the copper hydroxide undergoes any 

 change is doubtful, no change is probable until the 

 whole of the calcium hvdroxide has been neutralized, 

 when it may become changed to carbonate.^ 



Preparation. — Strict attention should be paid 

 to the instructions given below, for on the proper 

 mixing, and purity of the chemicals used, depends 

 the value of the resultino- solution as a funo-icide. 

 No exact formula can be given, as it is always 

 necessary to test the solution before applying, but 

 the following will be found about the correct pro- 

 portions : — ^ 



1 See "U.S. Dep. of Agr., Division of Vegetable Physiology and 

 Pathology Bull.," No. 9, 1896, and for more recent work, Pickering, 

 "Jour, of Agr. Sc," vol. iii. part 2, p. 171, and vol. iv. part 3, p. 273 ; 

 Gimmingham and Barker, "Jour, of Agr. Sc," vol. iv. part i, pp. 

 69 and 76 ; vol. 6, part 2, p. 220. 



- The amount of copper sulphate is sometimes reduced to equal 

 the amount of lime. 



