264 INSECTICIDES, FUNGICIDES, AND WEED KILLERS. 



that ammoniacal sulphate of copper, although more active agiinst 

 phylloxera than blue vitriol, does not kill it, and Pearson reports that 

 eau celeste removes the Macrodactylas subspinosus injurious to rose 

 bushes.] Along with all these properties just described eau celeste 

 has grave drawbacks. It is, above all, blamed for causing serious 

 burns, especially when the treatment has to be applied very early. 

 This fact is especially to be dreaded when eau celeste is spread in 

 moist weather when it therefore dries slowly on the leaves ; on the 

 other hand, when the sprayings are applied in the strong heat of 

 summer, this defect entirely disappears, and eau celeste is in every 

 way advantageous. These burns, in fact, are easily explained. It 

 has been seen under blue vitriol that the poisonous action of cupric 

 preparations on plants was the more pronounced the more soluble 

 they were in water. Eau celeste contains a cupric compound, as 

 soluble as blue vitriol, and the effect produced at the moment of 

 spx-aying is thus equally unfavourable to the plant. It is likewise 

 admitted that blue vitriol is poisonous, owing to the sulphuric acid 

 which it contains, and which, in bouillie bordelaise, is fixed and 

 rendered harmless by the lime. Although sulphuric acid may con- 

 tribute to a certain extent to the corrosive action of blue vitriol, it is 

 not the chief poisoning principle. For the same reason it is generally 

 admitted that eau celeste burns the leaves, because the sulphuric acid 

 of the blue vitriol used in its preparation is fixed by the ammonia, and 

 that this unstable salt, in decomposing, liberates sulphuric acid, which 

 then burns the leaves. This hypothesis is one of the chief reasons of 

 the use of copper carbonate in place of blue vitriol in the preparation 

 of eau celeste ; the latter, in fact, burns the plants much less than 

 ordinary eau celeste. 



There is thus great analogy between the action of blue vitriol and 

 eau celeste, both on the plants and on the fungi to be overcome. 

 From the beginning of the use of eau celeste it was to be seen that a 

 solution made from 0-5 per cent of blue vitriol sufficed to produce the 

 desired effect ; the doses have diminished in certain cases as far as 

 01 per cent of blue vitriol. With such solutions burns are no longer 

 to be feared. In contrast to blue vitriol, which, as it dries on the 

 surface of the leaf, forms small crystals, which dissolving in the dew 

 yield concentrated solutions, burning the leaves where these crystals 

 are accumulated, the eau celeste deposits cupric hydrate on evapora- 

 tion. The defect of burning the leaves only exists for the eau celeste 

 for the time during which the sheet of liquid takes to dry. As soon 

 as dry the ammonia which holds the copper oxide in solution evapo- 

 rates, leavmg a residue of cupric hydrate, which covers the surface 

 of the leaf and protects it against spores. If rain falls it is only 

 beneficial, because far from dissolving or detaching the cupric film, 

 it only dissolves and removes the sulphate of ammonia, the action of 

 which on the plant may be injurious. Eau celeste, compared with 

 blue vitriol solutions, therefore, possesses the advantage of leaving an 

 adherent deposit on the surface of the leaf, and whilst equally 

 efficacious at the moment of use, has a much more durable action. 

 With an equal dose of blue vitriol, it requires fewer sprayings with 



