Insecticides and Related Substances. 309 



tion in a white porcelain dish. A reddish brown precipitate or 

 color indicates the presence of soluble copper salts, and lime 

 should be added to the mixture until this no longer appears. 



The fungicidal properties of Bordeaux mixture are chiefly due 

 to the insoluble compounds formed and it is important to keep 

 these thoroughly in suspension. To facilitate this, the copper 

 sulphate and lime should be dissolved separately, each in one-half 

 the water, and when the lime is cool, they should be poured to- 

 gether with constant stirring. In this way, the dilute solutions 

 react to form a fine suspension which will not settle for several 

 hours. The chemistry of Bordeaux mixture has not been thor- 

 oughly investigated. According to Lodeman, when the copper- 

 sulphate is just neutralized, most of the copper is probably pre- 

 cipitated as a hydrate ; but excess of lime added to a concentrated 

 "mixture" forms another compound which may be a basic sul- 

 phate of copper and lime. 



Soda Bordeaux, made with caustic soda in place of lime in 

 the regular formula, has given satisfactory results. 



Copper ammonium sulphate, a clear blue solution formed 

 from copper sulphate and ammonia, also called "eau celeste," 

 has been applied as a fungicide, but its caustic action renders 

 it unsafe. Copper carbonate dissolved in ammonia, however, has 

 given good results. It should be freshly prepared, as the am- 

 monia may volatilize on standing, causing the copper to fall out 

 of solution. 



Copper sulphate has been applied to dormant trees and green - 

 house plants as a dilute solution, but it possesses a strongly acid 

 reaction and should be used with care. Smut on grains is de- 

 stroyed by this fungicide. A one to two hour immersion of oats 

 in a 0.5 to 1.0 per cent solution may be safely practiced, but 

 stronger applications retard germination. 



Potassium sulphide is used against mildews at the rate of 

 one-half ounce to one gallon of water. Strong solutions are 

 destructive to plants. Potash lye and formaldehyde-glycerine 



