126 Control of Parasites 



neutralize the acid of the copper salt, which would injure 

 the foliage, the reaction leaving a copper hydrate, which, dis- 

 solved in the carbonic acid of the air, is the active principle 

 in the fungicide. This solution should be used the day it 

 is prepared, and before using should be strained to avoid 

 trouble in the spraying nozzle. Since the Bordeaux mixture 

 is a disinfectant so useful that every gardener or owner of 

 trees should have it on hand and use it freely, it will save 

 time to make a stock solution of blue stone in the propor- 

 ^ tion of one pound to two gallons of water, when two and a 

 half gallons of this solution will be required to make a barrel 

 of mixture. The lime may also be slacked beforehand, in 

 the proportion of two pounds to one gallon, providing it is 

 kept under water until used. In this condition it is not 

 easily measured, although "half and half" will make about 

 the proper mixture; but it is well to apply a simple test to 

 show when sufiicient lime has been added to the blue stone. 



For this test an ounce of yellow prussiate of potash, 

 obtained from the drug store, is dissolved in half a pint of 

 water; if a few drops of this, added to the Bordeaux mix- 

 ture, produces a brown color, it shows that not enough lime 

 has been added. A simpler test is to hold a bright knife 

 blade in the solution for a minute or more: if it comes out 

 copper colored, more Hme is to be added. A small excess 

 of lime does no harm. Keep the solutions covered to pre- 

 \ vent evaporation. When the two solutions are mixed 

 \they should be used within twenty-four hours; separate, they 

 'may be kept through the season. 



There are now prepared limes in the market, powdered 

 or partly slacked, which, if fresh, are more effective and 

 more easily handled. 



Since the mixture is not really a solution but an emulsion, 

 which consists of minute insoluble particles of the sub- 



