74 THE DEPARTMENT OF AGRICULTURE. 



BORDEAUX MIXTURE. 



This is the most common copper fungicide, ft is made by mixing bluestone and 

 lime in various proportions which for brevity are expressed in a formula. Thus the 

 usual strength, which we may call the standard Bordeaux mixture, consists of 

 4 Ib. bluestone, 4 Ib. quicklime, and 40 imperial gallons of water. This is expressed, 

 shortly, " 4-4-40 Bordeaux mixture " ; the first figure referring to bluestone, the 

 second to lime, both in pounds, and the last to water in gallons. In United States 

 publications this strength would be expressed as 4-4-50 Bordeaux mixture owing to 

 the difference between the United States and imperial gallon. For potato-spraying 

 we generally use this strength, except for the earliest spraying, which it is generally 

 advisable to make 6-6-40. 



Bluestone is usually supplied in large crystals which dissolve rather slowly in 

 cold water, but rapidly in hot water. It may be dissolved fairly rapidly by tying it 

 in a piece of gunny-sacking and submerging it just below the surface of the water in 

 the barrel. If merely thrown to the bottom of the barrel of cold water it may be 

 days in dissolving. If Bordeaux mixture is going to be used regularly through the 

 season, it is most convenient to make up a stock solution of bluestone. A gallon 

 of water at 65 F. will dissolve about 3% Ib. In warm weather a stronger solution 

 still might be made, but it is liable to crystallize at the bottom, through evaporation 

 or during cooler weather. Two pounds to a gallon makes a convenient stock solution. 

 Twenty gallons of such a solution will provide the bluestone necessary for 400 gallons 

 of Bordeaux mixture. It is well to mark on the barrel the level of the liquid at the 

 beginning, and after measured amounts have been withdrawn, so that water may be 

 added to make up evaporation if necessary. 



Lime. Good fresh stone-lime is the best and cheapest to use. Hydrated lime 

 may be used, but about 50 per cent, more is required. In slaking lime just enough 

 water should be used to make it slake rapidly without the formation of powder, 

 which indicates burning. Watch the lime carefully during slaking and keep it 

 stirred. If the lime is not of the best quality it is better to slake it with hot water. 

 If the lime is good and the slaking done properly, the result should be a smooth 

 paste, which after the addition of water will strain readily. The lime may be made 

 into a stock solution, as in the case of the bluestone. It does not, of course, dissolve, 

 but forms a " milk of lime," from which the lime readily settles to the bottom of 

 the barrel. The liquid must therefore be thoroughly stirred before measuring out 

 a portion for Bordeaux mixture. 



To make 40 Gallons of 4-4-40 Bordeaux Mixture. Two barrels are required. 

 In one dissolve 4 Ib. bluestone or add the required amount of stock solution, according 

 to its strength. Add water to make up to 20 gallons. In the other barrel slake 4 Ib. 

 of quicklime or add the right amount of stock lime solution and make up to 20 gallons. 

 It is important that each of the two ingredients should be diluted in this way with 

 half the total amount of water required before they are mixed. A good enough 

 Bordeaux mixture will be made by now pouring either of the two barrels into the 

 other, but if help is available a better plan is to pour each barrel slowly, and at the 

 same time, into a third barrel or into the spraying-tank. This ensures thorough 

 mixing. If the strong solutions were first mixed and the extra water added after- 

 wards, the Bordeaux mixture would be coarse, settle rapidly in the spray ing- tank, 

 and not adhere well to the foliage, so that it would be easily washed off in wet 

 weather. The mixture, however made, must always be strained through a fine 

 strainer to take out any particles of grit which would otherwise clog the spray- 

 nozzles. Such a strainer should be supplied with the spray-machine. 



Testing the Bordeaux Mixture. As before mentioned, any free bluestone is very 

 injurious to foliage. If the lime used is good, the quantity given above is more 

 than enough to neutralize all the free bluestone. If, however, the lime is partly 

 air-slaked or otherwise poor, it might be insufficient, so that it is well to make a 

 practice of testing the mixture before applying it. Potassium ferrocyanide is the 

 simplest and best substance for this purpose. A little is dissolved in a small bottle 



