4 BULLETIN 866, IT. S. DEPARTMENT OF AGRICULTURE. 



The results of their laboratory tests, in which the re-formed copper 

 sulphate was determined after carbon dioxid had been passed through 

 the various basic sulphates, led Bedford and Pickering to believe that 

 the Formula. A spray, re-forming 40 per cent of the copper sulphate, 

 was from 12 to 15 times as effective as ordinary Bordeaux mixture 

 (Formula D), which re-formed 2.8 per cent of the copper sulphate, 

 and that the Formula C spray, re-forming 22 per cent of the copper 

 sulphate, was about 8 times as effective as the standard Bordeaux 

 (Formula D). 



These investigators (4) stated also that, "the efficacy of a fungicide 

 must not be estimated by the amount of copper contained in it, but 

 by the amount which becomes soluble and therefore available for 

 fungicidal action. Nor should the efficiency of a spray be judged by 

 the visible deposit left on the leaves, for even if it were composed 

 entirely of copper compounds it does not follow that it would be 

 more efficacious than some other deposit which might be invisible. 

 In most cases the deposit consists largely of material which is quite 

 inefficient and may be detrimental to fungicidal action, as is the lime 

 which constitutes four-fifths of the deposit visible after spraying with 

 ordinary Bordeaux mixture." Later they reported that the idea 

 that the fungicidal action of standard Bordeaux spray does not com- 

 mence until several days after its application had been definitely dis- 

 proved, and that the effects of the application of Bordeaux do not 

 become visible at once because time is necessary for the decay of the 

 tissues, which is the case even when a copper salt in solution is 

 applied, but that the excess of lime in ordinary Bordeaux causes the 

 fungicidal action to proceed more slowly. Pickering, however, be- 

 lieved that in ordinary or standard Bordeaux made with milk of 

 lime the copper reacts and undergoes on the tree the changes given 

 under the reaction for Formula D (p. 3). 



Swingle (23), Sicard (22), Bell and Taber (5), Vermorel and Dan- 

 tony (24), and others have discussed the chemical composition of 

 standard Bordeaux sprays, which are prepared by mixing a solu- 

 tion of copper sulphate with milk of lime. These two ingredients 

 are brought together in various ways, and the manner of mixing 

 undoubtedly affects the chemical and physical properties of the 

 spray. The details of the many theories covering the chemical 

 reactions which take place when copper sulphate and calcium 

 hydrate are mixed need not be considered here: 



Opposed to the belief held by Pickering and others that the copper 

 of Bordeaux is slowly made active by the carbon dioxid of the air 

 are the statements by Lutman (14) that Bordeaux mixture is 

 fungicidal immediately upon application. This writer considers that 

 the lime particles in Bordeaux have fungicidal properties. Swingle 

 (23), in 1896, advanced a series of ideas as to possible methods 



