2l6 



Minnesota Plant Diseases. 



the blade of a penknife in the mixture, allowing it to remain 

 for at least one minute. If metallic copper forms on the blade, 

 or, in other words, if the polished surface of the steel assumes 

 the color of copperplate, the mixture is unsafe and more lime 

 must be added. If, on the other hand, the blade of the knife 

 remains unchanged, it is safe to conclude that the mixture is 

 as perfect as it can be made. As an additional test, however, 

 some of the mixture may be poured into an old plate or saucer, 

 and while held between the eyes and the light, the breath should 

 be gently blown upon the liquid for at least half a minute. If 



FIG. 106. A gear-power f 



(Victor Spraying Machine.) 



the mixture is properly made, a thin pellicle, looking like oil on 

 water, will begin to form on the surface of the liquid. If no 

 pellicle forms more lime should be added." (B. T. Galloway.) 

 It is very important that good lime be used. Stock solu- 

 tions of the lime and copper sulphate may be prepared, and may 

 be kept several weeks without deteriorating. "To make stock 

 solutions, dissolve fifty pounds of copper sulphate in fifty gal- 

 lons of water. In another barrel slake fifty pounds of good 

 stone lime and add enough water to make fifty gallons. These 

 barrels should be tightly covered to prevent evaporation. 



