MATERIALS 35 



but the resulting emulsion is not so fine as when 

 lime is used. When the wash with iron is used, it 

 turns browai on the trees, owing to the formation of 

 rust. This does no harm whatever. 



For the iron and copper washes a special paraffin 

 oil (solar distillate, p. 43) should be used ; with the 

 soap wash any oil will do, at any rate, so far as making 

 a successful emulsion is concerned, but with solar dis- 

 tillate it is probably more effective than with ordinary 

 lighting oil. 



The iron emulsion, and also the soap emulsion, may 

 be bought in a concentrated form, requiring only 

 dilution and the addition of the soda to be ready for 

 use. Re-churning, however, is advisable, as mentioned 

 under Bordeaux mixture (p. 29). 



II. Lime. — As a winter wash, lime is in many 

 respects inferior to caustic soda : it is much less 

 energetic, and, to remove moss and lichen effectively, 

 the strength must not be reduced below lo per cent.; 

 it is advisable, indeed, to raise it up to 20 per 

 cent. : its action in destroying scale, even when used 

 at this strength, is generally less than that of the 

 caustic soda wash, and it appears to be diminished, 

 rather than increased, by the addition of paraffin oil. 

 Such strong lime-washes, moreover, cause much wear 

 of the spraying apparatus, and the whitened appear- 

 ance of the trees is considered by many to be objec- 

 tionable. On the other hand, lime-washing is held 

 to be the only means of diminishing the attack of 

 birds on fruit buds, and, when salt is mixed with it, a 

 wash is obtained which has been found to prevent the 

 hatching of the eggs of the apple-sucker {Psylla) : for 



