FUNGICIDES AND THEIR APPLICATION 89 



Physical properties. 



The physical properties of Bordeaux mixture are all- important, 

 since on the nature of the precipitate depends the adhesion of 

 the spray. In the freshly made mixture this should be fiocculent 

 or gelatmous in appearance, light blue in colour, settling very 

 slowly when allowed to stand. In a few hours the sediment 

 becomes more crystalline, settles quickly after shaking, and has 

 lost its power of adhesion when dried. This is the reason for the 

 customary warning to use only the freshly made mixture. The 

 flocculence of the precipitate can however be preserved to 

 some extent by adding skimmed or whole milk at the rate of 

 J pint (5 oz.) to the gallon, which also greatly increases adhesion. 



The nature of the precipitate originally formed depends to a 

 large extent on the method of preparation. The mixing of 

 strong solutions of copper sulphate and lime gives a very heavy 

 sediment, and should be avoided. The ordinary way is to 

 dissolve the copper in one half of the water, mix the milk of 

 lime with the other half, and then run the two together. This 

 gives a satisfactory result, is normally the most convenient, 

 and is least likely to go wrong in unskilled hands. It is quite 

 possible to get good results, and under some circumstances with 

 more convenience, by mixing one constituent with about five- 

 sixths of the water and adding the other with the rest. The 

 best result of all, according to O. Butler, is obtained from the 

 addition of weak copper solution to strong milk of lime. Should 

 strong milk of lime be added to weak copper or strong copper to 

 weak lime, it is essential that the liquid should be thoroughly 

 agitated during mixing. 



Solutions of copper sulphate must not be brought into contact 

 with metal vessels. For milk of lime this does not matter. The 

 prepared mixture can be contained in galvanised receptacles 

 provided it does not stand more than a few hours. When only 

 one wooden tub is available it may be used to contain the copper 

 sulphate and most of the water, the lime being added from a 

 bucket with vigorous agitation, or if the method of strong copper 

 to weak lime is adopted (which is less desirable) it is only neces- 

 sary to have a bucket made of wood, in which to dissolve the 

 copper, pouring the solution into the middle of the large re- 

 ceptacle containing the lime and water and stirring vigorously. 



The most satisfactory addition to Bordeaux mixture for 

 increasing its adhesion, valuable where sprayed foliage is exposed 

 to tropical rain, is resin soap. This is prepared by boiling 

 2 lb. of resin with i lb. of washing soda in i gallon of water 

 until the mixture is clear, and adding this quantity to 25-30 

 gallons of Bordeaux as found necessary for the purpose in hand. 

 This also improves the wetting and covering power of the mixture 

 on such leaves as resist in these respects the ordinary type of 

 wash. It is possible that a weak Bordeaux with this addition 

 may be found to be as effective as a strong one without it. 



