No. 6. DEPARTMENT OF AGRICULTURE. 519 



Uuie. testing after each addition, uiitil the sulphate has all beeu ueu 

 trali^ed. From the quantity of lime thus used the necessary dilu- 

 tion can be calculated to make the lime milk any desired strength. 

 The proportion of water necessary to make the proper dilution will 

 be equal to the difference between the required strength and the 

 qu.\ntity of lime milk used to neutralize the sulphate, expressed in 

 fractions of that strength. Thus, if one-half pint is used in the 

 neutralization, and if it is desired to have the lime of the same 

 strength as the sulphate solution, it will require one-half pint of 

 water for each one half pint of lime milk; therefore, the total quan- 

 tity of the latter will simply have to be doubled, by adding an equal 

 quantity of water. If only one-quarter pint was necessary to ac- 

 complish the neutralization, the total would have to be quadrupled, 

 or three times the quantity of water added. In large-scale opera- 

 tions this standardizing of the lime milk will be found very advanta- 

 geous, especially where the mixing is not all done by the same man. 

 In this case, the standardizing can be done by the foreman, or head 

 operator, and then the spray crews have simple, straight measuring 

 to do." 



Another very simple test for determining the sutticiency of lime is 

 the so-called knife-blade test. This test consists of simply placing 

 the end of a bright knife-blade, key or other steel object in the mix- 

 ture. If too little lime has been used in the mixture the bright steel 

 will be coated with metallic copper, or copper-plated, while if enough 

 lime is present to combine with all the copper sulphate no such plat- 

 ing will take place. The making of these tests are impoitant; for it 

 must be emphasized that there must be no free copper sulphate in the 

 completed Bordeaux mixture. In order to be absolutely certain of 

 this it is best to use an excess of lime milk, which does no harm. In 

 fact, for use on tender foliage, such as peaches and Japanese plums, 

 it is necessary to prepare the mixture with a large excess of lime 

 milk in order to avoid injury. 



Bordeaux mixture belongs to the class of spray washes which .con- 

 sist of insoluble substances in suspension in water. All the pre- 

 cautions, then, mentioned before regarding this class of mixtures 

 are applicable and must be observed. But in this case a good deal of 

 the difficulty in maintaining the compound in suspension may be 

 avoided in the preparation of the fungicide. That is, it is possible so 

 to mix the two ingredients that the resulting precipitate will settle 

 slowly, and may thus be kept in suspension with a minimum effort 

 of agitation. Plates IX and X exhibit the effects of different 

 methods of preparing Bordeaux. The photographs were taken after 

 allowing the mixtures to settle twenty minutes and one hour respec- 

 ti\ely. The mixture in the left-hand cylinder was prepared by mix- 

 ing dilute copper sulphate solution and dilute lime milk together. 

 The right hnnd mixtnro was made by mixing the concentrated solu- 



