36 FRUIT TREES AND THEIR ENEMIES 



that purpose, however, it is best applied a few weeks 

 before the buds expand, when it must be regarded 

 rather as a spring, than as a winter wash : an apph'ca- 

 tion at that date would be too late to prevent the 

 depredations of birds. 



In every case where lime is mentioned in this 

 volume, the weights refer to that of the quicklime, 

 and in every case this quicklime should be slaked 

 before anything further is done to it. Failure in 

 obtaining satisfactory results with preparations of 

 lime are nearly always to be traced to want of care 

 in starting with quite freshly burnt lime, or in slaking 

 this. Quicklime is an oxide of calcium, which com- 

 bines chemically with one-third of its weight of water 

 to form calcium hydroxide, or slaked lime, a compound 

 corresponding with caustic soda. The combination oc- 

 curs only slowly at first, but much heat is developed by 

 it, and if this heat is not dissipated, the whole becomes 

 very hot, and then the action proceeds rapidly, the 

 lime all crumbling up into a fine powder. If too much 

 water is added at first, the rise of temperature is pre- 

 vented, and the slaking takes place very slowly and 

 imperfectly, hard lumps of unslaked lime being left 

 in the product. In slaking, therefore, only just enough 

 water should be added to wet the lime, without any 

 actual water being left over ; and, if the lime does not 

 become very hot, and crumble up in about ten minutes, 

 a fresher sample should be procured. Air-slaked lime 

 should never be used, for that always contains an 

 unknown proportion of carbonate (chalk), which is 

 useless for insecticidal purposes. 



After the lime has been properly slaked, it may 



