156 THE AMERICAN PEACH ORCHARD 



Copper sulphate is seldom adulterated, though 

 sometimes it is not so clean as it ought to be. The 

 granulated form costs about one-half cent more a 

 pound than the lumps, and is easier to dissolve. If 

 the amount of work to be done will justify it the 

 copper sulphate should be bought by the barrel. 

 A barrel contains in the neighborhood of 200 pounds 

 and costs from 6^ to 7^ cents a pound at present, 

 with a tendency for the price to go higher. 



The proper selection of lime is more important. 

 The lime must be of good quality, well burned and 

 not air slaked. The fine lime sometimes preferred 

 by masons should not be used. Lumps are better. 



Always use lime enough. The quantity recom- 

 mended in the formula already given will be suffi- 

 cient, if good lime is used ; but in case of doubt more 

 lime can be used. It is customary in books and 

 bulletins to recommend the so-called ferro-cyanide 

 test, but in actual practice it is better to rely on 

 good lime. The idea of this ferro-cyanide test is to 

 determine whether the lime has completely neutral- 

 ized the copper sulphate. A solution of potassium 

 ferro-cyanide (yellow prussiate of potash) is made 

 by dissolving say one ounce of the ferro-cyanide in 

 six ounces of water. A few drops of this solution 

 may be dropped into the Bordeaux mixture to be 

 tested, when, if the copper sulphate has not been 

 neutralized, it will instantly give a deep brownish- 

 red color. If the mixture is properly neutralized no 

 color will appear. This test is very accurate and 

 reliable, provided the Bordeaux is evenly mixed; but 

 it is too much bother for practical use in the field. 



Bordeaux mixture is nowadays seldom used on 

 peach trees when in foliage ; but in case it is to be 

 applied to the leaves it should be made considerably 



