CHAPTEE X. 



IRON PEROXIDE — IRON BOUILLIES — IRON SULPHIDE — IRON 

 CHLORIDE — GREEN VITRIOL — POTASSIUM FERROCYANIDE — 

 PRUSSIAN BLUE. 



65. Hydrate of Sesquioxide of Iron (Ferric Hydrate), Feo(HO),;. 

 — Preparation, — By precipitating a solution of sulphate of iron (green 

 vitriol) by caustic alkali or by milk of lime. 



FeSO, + 2K0H = Fe(OH)., + K.SO,. 

 FeSO, + Ca(OH), = Fe(OH), + CaSO,. 



The hydrate of the protoxide of iron, ferrous hydrate, a greenish-white 

 precipitate which is first formed, oxidizes afterwards in contact with 

 the air, and is converted into hydrate of sesquioxide of iron ferric 

 hydrate, which is yellowish-brown. 



2Fe(0H), + H,0 + = Fe,(OH),, 



The bouillies used against plant diseases 'were made from 1-15 lb. 

 of green vitriol and 4-8 lb. of quicklime per 10 gallons of water. 

 Their preparation is similar to the bouillie bordelaise. The green 

 vitriol is dissolved in 5 gallons of water, and the quicklime made into 

 milk of lime is run with 5 gallons of water into the green vitriol 

 solution with suitable stirring. The bouillie should have a slight 

 alkaline reaction. 



Properties. — -The ferric bouillie has the physical properties of the 

 bouillie bordelaise and behaves like the latter, both as to its adherence 

 and the solubility of its precipitate by atmospheric agents. 



Action of the Ferric Bouillie on Plants. — There exists between 

 the iron bouillie and sulphate of iron (green vitriol) the same relation 

 as between bouillie bordelaise and sulphate of copper (blue vitriol). 

 The sulphuric acid of the sulphate of iron being neutralized is in an 

 inert and insoluble form ; the sulphate of lime does not scorch the 

 leaves like green vitriol solutions exceeding 2 per cent. But the 

 hydrate of sesquioxide of iron engulfed in the sulphate of lime, and in 

 an excess of lime, has not however such a rapid action on the chlorotic 

 condition of the plants treated as solutions of green vitriol. Dufour 

 has shown that iron placed in contact with the plant in this slightly 

 soluble form is none the less absorbed wherever the leaf is touched 

 by the ferruginous bouillie. Chlorotic plants after several sprayings 

 with this bouillie show green places at all points of contact. Never- 

 theless, the effect of these bouillies is nil if a strong dose of sulphate 



(168) 



