152 INTERNATIONAL CONGRESS OP VITICULTURE 



precipitated as the basic sulphate 10 CuO SO 3 ;2 in the latter 10 CuO SO 3 

 predominates though depending on the strength of the mixture in cupric 

 sulphate and the care with which it was prepared either the next lower or 

 higher basic sulphate may be present to some extent. 



The slightly alkaline Bordeaux mixtures are prepared by combining the 

 cupric sulphate and calcic oxide approximately in the ratio of 3:1 and are 

 represented by the so-called "neutral" Bordeaux mixture of practice, which 

 consists largely of 10 CuO SO 3 . 



The alkaline or basic Bordeaux mixtures are those washes in which the 

 lime occurs in considerable excess, the ratio cupric sulphate to calcic oxide 

 ranging between the limits 2:1 and 0.5:1. The copper precipitate in these 

 mixtures, at least when they contain more than 0.5 per cent cupric sulphate, 

 consists largely if not entirely of 10 CuO SO 3 . 



We have seen that in all three types of Bordeaux mixture recognized in 

 practice the copper is precipitated very largely in the form of the basic 

 sulphate 10 CuO SO 3 . It should, however, be noted that this is only true 

 in general for mixtures that have been recently made, Bordeaux mixtures be- 

 ing, with one exception, i. e., Woburn Bordeaux mixture, quite unstable, 

 while for all practical purposes Woburn Bordeaux mixture may be consid- 

 ered stable, all other forms of Bordeaux mixture deteriorate more or less 

 rapidly depending on their strength in cupric sulphate, the ratio cupric 

 sulphate to calcic oxide used in preparing them, and the temperature at 

 which the washes are kept, as will be seen from the following table: 



Table I. Effect of temperature, strength in cupric sulphate, and ratio cupric 

 sulphate to calcic oxide on the rate of deterioration of Bordeaux mixtures. 



Temperature Strength of Mixture Ratio Time Required 



of in Cupric Suiphate Cupric Sulphate for 



Mixture Per Cent Calcic Oxide Deterioration 



25 C. 4 1:1 16 



9 C. 4 1:1 96 



9 C. 4 1:0.5 121 



25 C. 2 1:1 21 



9 C. 2 1:1 192 



9 C. 2 1:0.5 240 



25 C. 1 1:1 8 



9 C. 1 1:1 168 



9 C. 1 1:0.5 192 



25 C. 0.5 1:1 5 



9 C. 0.5 1:1 72 



9 C. 0.5 1:0.5 336 



9 C. 0.5 1:0.2 



On standing, for instance, the so-called "acid" and "neutral" Bordeaux 

 mixtures gradually decompose" with the formation of cupric oxide, while the 

 copper precipitate in the basic Bordeaux mixtures, which is highly gelatinous 

 in the freshly prepared washes, gradually changes over into a copper salt, 

 as yet unidentified, which forms blue sphaero-crystals. The three types of 



2 For the chemistry of Bordeaux mixture see: 



Pickering, S. U., The Chemistry of Bordeaux Mixture, Journ. Chem. Soc. 

 (Transactions) 91:pt. 2, 1907. 



Bordeaux Spraying: Journ. Agr. Science 3.171 et seq. 1908-10. 



Bedford, Duke of, and Pickering, S. U. Woburn Experimental Fruit 

 Farm Report 11, 25 et seq. 1910. 



