30 FRUIT TREES AND THEIR ENEMIES 



gradually, and the addition stopped as soon as the 

 green-blue colour of the precipitate changes to a full 

 blue. It is not safe, however, to rely on this change 

 of colour, as it is not always well marked, and it is 

 better to test the liquid at intervals with ferrocyanide, 

 as described above, during the addition of the lime. 

 If the lime is quite fresh, and if the slaking has been 

 carefully done, it will be found that little more than 

 half the quantity mentioned in the formula will suffice 

 to precipitate the whole of the copper. 



Bordeaux mixture made with milk of lime may 

 be emulsified with paraffin in the same way as that 

 made with lime-water, though it does not make such 

 a perfect preparation. 



Both the Bordeaux mixtures here described are 

 equivalent in fungicidal value to that known in 

 America as the ** normal" or '' vG'' mixture. In 

 England, weaker mixtures are often used, and, if such 

 are required, the amount of copper sulphate may be 

 reduced, reducing that of the lime in the same pro- 

 portion. The writers, however, have rarely found any 

 serious injury to be done to the foliage by mixtures 

 of the ''normal" strength, when carefully made. 

 Many recipes recommend the use of a large excess 

 of lime, under the mistaken impression that it will 

 prevent scorching : this is not the case. A full in- 

 vestigation of the nature and action of Bordeaux 

 mixture will be found in the Eighth Report of the 

 Woburn Experimental Fruit Farm. 



Caustic winter washes. — These should be used 

 only on the trees in the dormant state, the object of 

 their use being to remove moss, lichen and dead bark, 



