POTASSIUM FEREOCYANIDE. 187 



(apple blossom weevil). — Mohr advises to kill this insect in winter when 

 it seeks refuge in the inequalities of the bark, to scrape the trunk, collect 

 and burn the bark, and coat the whole trunk afterwards with a pasty 

 mixture of 20 lb. of green vitriol, 10 gallons of water and a sufficiency 

 of potters' clay. Spraying with a 20 per cent solution of green 

 vitriol would appear to be as efficacious as liming the trees or Balbiani's 

 coating. 



Cochylis amhignella, Hubn. (tortrix of the vine). — The grubs resist 

 somewhat concentrated solutions of green vitriol. A 2-3 per cent 

 solution has no effect (Mohr), nor a 10 per cent solution (Dufour), 

 Martini diminished the Cochylis 27 per cent by winter decortication 

 followed by coating with a 45 per cent solution of green vitriol and 

 1 per cent of phosphoric acid. 



Tijjula pratensis, L. (meadow gnat). — The larvae of the tipula, which 

 cause ravages in meadows and lawns, are killed by green vitriol : it is, 

 however, preferable to till the meadow, spread green vitriol, and sow 

 again. 



Ajyhides. — Naked plant lice are sensitive to the action of green vitriol. 

 A 1 per cent solution kills them (Mohr). On fruit trees injected with 

 green vitriol and conveying this product in their sap, cochineals- 

 such as Diaspis fallax and Mytilasjns pomorum, which live on this 

 sap, gradvially disappear. Mohr found that the larvae of the woolly 

 aphis Schizonevra lanigera, Hausmann, are killed by an emulsion of 

 green vitriol 1 lb., amyl alcohol 5 lb., water 10 gallons. The action 

 of green vitriol on phylloxera is nil. 



Nematodes. — Green vitriol applied in large doses as manure on in- 

 fested fields kills nematodes (Zimmermann). 



Eartk-ivorms (Lombricus) are also destroyed by green vitriol, which 

 can be mixed with the manure. 



Snails and Slugs. — Slugs are very sensitive to green vitriol. TO' 

 destroy them sow a mixture of green vitriol and sand in the evening, 

 preferably in wet weather, on the soil frequented by snails and slugs. 

 Eouzaud advises to protect vine buds from slugs to coat the stem' 

 with a solution of green vitriol, which penetrating through the mucous 

 of the slugs kills them if they climb on a stem treated in that way. 



69. Ferric Sulphate, Fe.,(S04)3. — Preparation. — By heating 100 

 parts of green vitriol, 100 parts of water, and 20 parts of sulphuric 

 acid, then adding nitric acid until no more brown fumes appear. The 

 brown solution on evaporation yields a yellow salt. 



Properties. — Soluble in water and endowed with the disinfectant 

 properties of green vitriol. 



Use. — Griffiths particularly recommends it against parasitic fungi. 

 As a tonic he regards it as superior to green vitriol because it is more 

 directly assimilable by the roots. 



70. Ferrocyanide of Potassium (yellow prussiate). — Prepara= 

 tion. — By calcining blood in closed vessels with potassium carbonate 

 potassium cyanide is formed and removed by lixiviating the mass with 

 boiling water. The lye is then boiled with iron in contact with air ; 

 there is absorption of oxygen and yellow prussiate is formed. The 

 crystallized salt is obtained by concentration and evaporation. 



