Bordeaux Mixture 73 



the excess lime in solution. There must be 

 lime enuf present to precipitate all the cop- 

 per before there can be any left over to 

 react with carbon dioxid so that the forma- 

 tion of a white scum is proof that no copper 

 remains in solution and that the mixture 

 does not contain any soluble copper that can 

 burn fohage. 



Bordeaux mixture protects plants from 

 attacks of fungous diseases. When spread 

 over the leaf it dissolvs very slightly and 

 disease spores blown on by the wind are 

 kild upon germination by the soluble copper 

 formd. 



The substances which act upon the Bor- 

 deaux to make the copper soluble, to the best 

 of our present knowledge, are the carbon 

 dioxid, the ammonia and the nitric acid 

 present in the atmosphere. The carbon 

 dioxid first combines with hme forming in- 

 soluble calcium carbonate and following this 

 begins the conversion of the copper to basic 

 copper carbonate which is accompanied by 

 the Hberation of copper sulfate. Basic cop- 

 per carbonate is dissolvd by more carbon 

 dioxid, by ammonia, by nitric acid, or by 

 ammonium nitrate made from the ammonia 

 and nitric acid. The amount of soluble cop- 

 per produced by the atmospheric agencies 

 is very small, — thousandths or ten-thou- 



