SOLUBLE BORDEAUX FOR POTATO BLIGHT. 

 Chas. D. Woods. 



In the preparation of Bordeaux mixture from slacked lime and 

 sulphate of copper, a chemical change takes place whereby 

 hydrate of copper and sulphate of lime (gypsum) are formed. 

 Both of these materials are insoluble in water, and Bordeaux 

 mixture consists of these materials mechanically suspended in 

 water. The gypsum is so heavy that, unless the mixture is kept 

 thoroughly stirred, it will speedily separate out and bring down 

 with it the lighter hydrate of copper. This necessitates the use 

 of an agitator, and much of the unsatisfactory work of the 

 spray as applied by some of the outfits on the market is due to 

 imperfect agitation. Commercial Bordeaux mixtures have been 

 made in which part of the gypsum has been taken out. Such 

 mixtures are more easily kept in suspension, but there has not 

 been sufficient gain to compensate for the extra labor involved 

 in the preparation of such Bordeaux mixtures. For many years 

 it has been known that the addition of sugar would render the 

 hydrate of copper soluble. If the sugar is added to the slacked 

 lime and allowed to stand for some time before adding it to the 

 sulphate of copper solution, hydrate of copper, soluble in water, 

 with only a trace of gypsum results. 



Obviously Bordeaux in solution would present many desirable 

 features. The director of the Wisconsin Experiment Station 

 wrote that they were to experiment during the season of 1904 

 with such a Bordeaux mixture and invited the co-operation of 

 this Station to test its efficacy upon potatoes in order that data 

 might accumulate faster. Some of the possible merits of this 

 new Bordeaux mixture were pointed out as follows : 



"It is believed, on account of the soluble condition of the 

 copper hydrate in this preparation, that its efficiency as a fungi- 

 cide will be much greater than in the ordinary Bordeaux mix- 

 ture, and consequently that it may be diluted at least ten and 



