Plants as Affected by Fungous Parasites. 183 



per compounds are more generally satisfactory, since 

 they have the greater adhesive power. 



329. The Bordeaux Mixture, which consists of a 

 compound of copper sulfate (324) and lime, is now ex- 

 tensively used to prevent many fungous diseases of 

 this class. A standard formula for the Bordeaux mix- 

 ture is : 



Dissolve 5 pounds of copper sulfate in 25 gallons of 

 water by suspending it in a bag of coarse texture near 

 the surface of the water ; slake 5 pounds of fresh quick- 

 lime in sufficient water to form a paste and dilute to 

 25 gallons. Pour the two solutions together. 



Metal vessels, other than those of brass or copper, 

 should not be used. 



Prepared by the above formula, the Bordeaux mix- 

 ture often contains more lime than is needed for the 

 chemical action that occurs. To avoid this excess of 

 lime, a chemical test may be used, as follows : Pour 

 only hall of the slacked lime and water into the cop- 

 per-sulfate solution, stir well, and add a few drops of 

 a 20 per cent solution of potassium ferrocyanid. If a 

 rich, reddish-brown color is produced, add more lime. 

 Continue to test and add lime until the reddish-brown 

 color no longer appears. Then add a little more lime, 

 as a slight excess of lime is desirable. A bright, clean 

 knife blade may also be used as a test. If a slight film 

 of copper forms upon it when placed in the mixture, 

 more lime is needed. The Bordeaux mixture is prefer- 

 ably strained before use, and should be kept well stirred 

 during its application (304). It may be applied with 

 any good spray pump. 



