42 The Spraying of Plants. 



Millardet and Gayon in 1887 conceived 1 the idea of making 

 the Bordeaux mixture on a new plan. This consisted in leav- 

 ing about the tenth of one per cent of dissolved copper sulphate 

 in the mixture. As comparatively little was heard of this prep- 

 aration, it is probable that the difficulty of its preparation was 

 one reason why it was not more extensively used. But others 

 were at work upon the problem and it was eventually solved. 



B. Pons, a chemist at Limoux (Aude), worked at it from a 

 chemical standpoint. 2 He took advantage of the fact that when 

 concentrated solutions of sugar and of copper sulphate are 

 mixed with each other, there is eventually formed a precipitate 

 which is a true sulphosaccharate of copper. This precipitate, 

 when dry, is in the form of a very fine, bluish-white powder. 

 Pons modified it in such a manner that the amount of dis- 

 solved copper in the Bordeaux mixture could be regulated by 

 the varying amounts of the powder used. His directions for 

 preparing the mixture were as follows: 



Dissolve 2 kilos of this powder in 90 liters of cold water. 

 Agitate for five to fifteen minutes. Add to this liquid, while 

 stirring well, 1 kilo of quicklime freshly slaked in 10 liters of 

 water. Stir the mixture for about five minutes and it is then 

 ready for use. At first it entirely resembles the Bordeaux mix- 

 ture as commonly prepared, but when this precipitate is allowed 

 to settle the liquid above the sediment is of a blue color, whereas 

 in the common Bordeaux it is clear. One-fourth of the copper 

 contained in the mixture is held in solution in this "Bordeaux 

 mixture celeste " ; the preparation was so called by Pons. 



Pons sent some of this powder, which he called the sulpho- 

 saccharate of copper, to Millardet and Gayon in October, 1889, 

 for the purpose of having it tested. 3 They described it as a 

 blue powder, as fine as ashes, but homogeneous in character. 

 When prepared, the mixture was very alkaline, and the pre- 

 cipitate was finer and more abundant than that found in the 

 Bordeaux mixture. On this account the solid matter settled 



1 Millardet et Gayon, "Considerations raisonnees stir les divers Precedes de 

 Traitement du Mildiou paries composes cuivreux," 188T, 14. See, also, E. Macb, 

 " Bericht fiber die Ergebnisse der im Jahr 1886 ausgefuhrten Versuche zur Bekiirnp- 

 fung der Peronospora," 1887, 20. 



2 Jour. (TAg. Prat. 1889, Dec. 12, 866. See, also, Barreswil, Jour, de Pharm- 

 acie et de Chemie, 3me serie, vii. 1845, 29. 



3 Ibid. 1890, Feb. 20, 269. 



