176 Principles of Plant Culture. 



add enough water to make 45 gallons of the whole. Metal 

 vessels, other than those of brass or copper, should not 

 be used. 



The hot water hastens the dissolving of the copper 

 sulfate. Cold water may be used by suspending the 

 sulfate in it in a sack of coarse texture a day or two in 

 advance. 



Prepared by the above formula, the Bordeaux mixture 

 often contains more lime than is needed for the chemical 

 action that occurs. To avoid this excess of lime, a chem- 

 ical test may be used, as follows : Pour only half of the 

 slacked lime and water into the copper-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 Bor- 

 deaux mixture is preferably strained before use, and 

 should be kept well stirred during its application. It 

 may be applied with any good spray pump. 



The arsenical compounds (284) may be added to the 

 Bordeaux mixture, and thus a single treatment will serve 

 for both insects and fungi. 



330. The Diseases Preventable by Bordeaux Mixture are 

 the apple and pear scab (328), the downy mildew and 

 black rot* of the grape, the early f and late blight J of 

 the potato, the gooseberry mildew,* the leaf- blight of the 

 pear,f and some others. 



* L&stadia BidwellH. f Macrosporium Solani. % Phytophthora infestans. 



