54 DISEASES OF CULTIVATED PLANTS 



enabled us to clearly understand in what particular way 

 Bordeaux mixture acts as a fungicide, and also the special 

 mode of preparation which results in the greatest amount of 

 benefit, combined with the minimum amount of injury to the 

 host-plant. The following is an abstract of that portion of 

 Mr. Pickering's investigation that appeals to those desirous of 

 preparing the most effective kind of Bordeaux mixture. Those 

 desirous of understanding the why and the wherefore are 

 referred to the original account, contained in the Eighth 

 Report of the Woburn Experimental Fruit Farm, 1908. 



The object to be aimed at in making Bordeaux mixture 

 should be to reduce the lime to the lowest possible propor- 

 tions consistent with the precipitation of the whole of the 

 copper present ; any excess of this means so much loss of 

 efficiency, and so much money thrown away. 



When milk of lime is used it is impossible to adjust the 

 quantity so as to attain this end, but it is perfectly simple to 

 do so by using clear lime water, and lime dissolves in water 

 to the right extent to make Bordeaux mixture of very nearly 

 1 normal ' strength. 



One hundred gallons of such a mixture is prepared as 

 follows: Dissolve 6 lb. 6\ oz. of crystallised copper sulphate, 

 by suspending it in a piece of sacking, in two or three gallons 

 of water in a wooden or earthenware vessel. Take about 

 three pounds of good quicklime and slake it in a little water, 

 then put it into a tub with 1 20 gallons of soft water. Stir the 

 lime and water, then leave it to settle until the liquid is quite 

 clear. Run off 86 gallons of the clear lime water and mix it 

 with the copper sulphate. This i^ .1 little stronger than 

 'normal' Bordeaux mixture. To reduce it to that strength, 

 make up to ioo gallons with soft water. 



However Bordeaux mixture is made, it is important to make 

 sure that all the copper is thrown down. The most certain 

 test that fruit-growers can use 1^ to put a few drops of a solu- 

 tion of potassium ferrocyanide into a white saucer with some 

 water, and to drop into this some of the clear liquid after the 

 Bordeaux mixture has settled. A red or brown colour shows 

 that there is copper in solution, and more lime water must be 

 added until the test shows no coloration. 



Among the advantages in favour of thus preparing Bordeaux 

 mixture are the following: Acting at once as a fungicide; 

 whereas it appears to have been well established that ordinary 

 Bordeaux mixture prepared with milk of lime has no fungicidal 



