1!^S ixsKCTU ii)i:s, 1 rxdiciDEs, and wked killers. 



Use. — Mouillel'ert tried yellow prussiate on Fliylloxcra rastatrix. 

 He watered a phylloxera-infested vine in a pot containing 3 litres of 

 earth with a 2 per cent sol u lion. At that strength yellow prussiate 

 Tiilled all the phylloxera. Mouillefert renewed his trials on the large 

 scale. He laid down 100 grammes (34 oz.) of prussiate around each 

 stock and afterwards applied water. The results confirmed the poison- 

 ous action of this substance. Unfortunately, it is not without effect 

 on the plmts and it temporarily injures the vine. Knop formerly 

 showed that if yellow prussiate was capable of imparting to the plant 

 the iron which it required, it was, on the other hand, often injurious to 

 it. He made the curious observation that the prussiate added in small 

 ■dose to no matter what nutritive liquid stopped grow^th forthwith of 

 the plants in no matter what stage of growth. Without dying the 

 plant appeared to stop growth ; it subsisted but showed no growth. 

 It follows from the experiments of Bahadur (?) that yellow prussiate 

 is a very feeble poison to young plants and absolutely harmless to 

 fungi when used in the dark. It is quite otherwise in the light. It 

 decomposes with formation of prussic acid which renders it poisonous. 



71. Prussian Blue (ferric ferrocyanide). — Discovered at Berlin, 

 1710. — ^Preparation. — By acting on yellow piussiate with a ferric salt. 



Properties. — -Prussian blue is a precipitate insoluble in water but 

 soluble in oxalic acid. Weak acids do not decompose it, but strong 

 acids and caustic alkalies destroy it. 



Use. — Prussian blue in paste was used in 1894 by Galloway and 

 Fairchild. The former tried it against rust of cereals, the second to 

 prevent Entomosporltim iiiaculatum, Lev. (spots of the leaves of the 

 pear-tree). Although the adherence of this paste was superior to that 

 •of bouille bordelaise, Galloway found that Pi ussian blue possessed no 

 anticryptogamic property owing to its absolute insolubility in atmos- 

 pheric agents. In spite of a large number of sprayings the fields of 

 oats and summer wheat were invaded by rust. Fairchild, however, 

 remarked a certain action on the pear-trees treated, although much 

 weaker than modified eau celeste. 



72. Borate of Iron, FeB^O-. — Preparation. — By adding borax 

 to a ferrous salt. A grey precipitate is formed which turns yellow 

 rapidly by oxidation. Fairchild prepares a borate of iron paste by 

 •dissolving 6 lb. of dry green vitriol in oO gallons of water and adding a 

 solution of 24 lb. of borax in 50 gallons of water. Fairchild tried this 

 paste against Ent()7nos2)orum maculatum (spots of the leaf of the pear) 

 and against Flii/llosticta s-phcerojinidea, E. and E. (spots of the leaf of 

 the chestnut). This paste behaved like all pastes containing insoluble 

 iron, that is to say, without action on the spores of fungi they are 

 ■somewhat injurious to vegetation. Galloway's experiments to combat 

 rust of oats and summer wheat with this bouillie also gave negative 

 I'esults. 



