158 INTERNATIONAL CONGRESS OF VITICULTURE 



agency would knock them off. On the other hand, in the moderately alka- 

 line Bordeaux mixtures, i. e., washes in which the ratio cupric sulphate to 

 calcic oxide varies between 1:0.5 and 1:1, the precipitate is no longer homo- 

 geneous but contains in admixture a considerable number of calcic hydrate 

 particles which effectively prevent the fissuring and curling of the spots on 

 drying; the calcic hydrate particles play a similar role to sand in cement. 



Again, in the Bordeaux mixtures in which the ratio*upric sulphate to 

 calcic oxide is greater than 1:1 the spots on drying do not fissure or curl, 

 but their adhesiveness decreases for the same reason, I presume, that an 

 excess of sand weakens cement. 



The adhesiveness of Bordeaux mixtures is affected, however, not only 

 by the ratio cupric sulphate to calcic oxide used in their prepartion, but 

 by the length of time elapsed between the time of prepartion and the time 

 of application, the temperature of the water used, the relative dilution of 

 the copper sulphate solution and the milk of lime, and the manner in which 

 the two are combined. 



Let us first of all inquire what effect the method of preparation has 

 on the adhesive properties of Bordeaux mixtures. It has been shown by 

 Gastineio that the method of mixing Bordeaux mixtures affects their adhes- 

 iveness as will be seen from the following table. 



Table VIM. Effect on method of mixing on adhesiveness of Bordeaux 



mixture. 



Adhesiveness of freshly 



prepared mixtures; 



Method of Mixing. Relative numbers 



Copper and lime equally diluted and poured together 



simultaneously 100 



Strong lime to weak copper 92.5 



Strong to strong 54.6 



The method of mixing Bordeaux mixture not only affects its adhesiveness 

 as the above table shows, but we also have abundant evidence to show that 

 the method of mixing employed also affects the rate of settlement of the 

 precipitate formed. It would seem, therefore, that one is justified in assum- 

 ing that a close relation exists between rate of settlement and adhesiveness, 

 though the data at present available are not sufficiently extensive to warrant 

 one drawing definite conclusions regarding the superiority of any one method 

 of prepartion to the exclusion of all others. If one prepares, for instance, a 

 series of 1 per cent Bordeaux mixtures (1:1) as per the following methods: 



1. Strong lime to strong copper 



2. Strong lime to weak copper 



3. Weak lime to strong copper 



4. Lime to copper equal strengths 



5. Lime and copper equal strengths poured together simultaneously 



6. Copper to lime, equal strengths 



7. Weak copper to strong lime 



8. Strong copper to weak lime 



9. Strong copper to strong lime.il 



he will obtain the results indicated in the following table, a perusal of 

 which will show that there are at least four methods of mixing 1 per cent 



lOLoc. cit. 



11 The mixtures were prepared as follows: 



In method 1 the requisite amount of a stock solution of cupric sulphate 

 was taken and water added to 30cc.; the calcic oxide was freshly slacked 



