COPPER SULPHATE (BLUE VITRIOL). 207 



compounds are capable of coagulating albumen and other nitrogenous 

 substances with which the life of the plant is intimately linked. The 

 intensity of their toxic action is in inverse proportion to their atomic 

 weight ; but keeping to these proportions blue vitriol is ten times more 

 energetic than green vitriol, and mercuric bichloride 100 times more 

 active than the last. The same holds good as regards the stimulating 

 effect, that is to say, that to increase the assimilation in a plant it 

 requires 100 times less mercury and ten times les-i copper than of iron. 

 These salts are, moreover, not the only ones capable in small doses 

 of stimulating the vital functions of the plant. M. N. Ono found that 

 poisonous salts, such as zinc sulphate, cobalt sulphate, sodium 

 fluoride, and nickel sulphate, had in small doses lost their poisonous 

 properties and become stimulants. Raulin found the same with salts 

 of zinc and of silicium. 



In practice it has been found that blue vitriol may render the same 

 service as green vitriol, but that for this purpose it must be used in 

 much smaller quantity. The analogy between the action of these 

 two salts is so striking that it has been seriously a question of attri- 

 buting this action to the green vitriol, very often present in commercial 

 blue vitriol ; they have even gone so far as to advise the addition of a 

 little green vitriol to blue vitriol to increase its stimulating action. 

 A manifest error was thus committed, which will be dealt with when 

 the action of bouillie bordelaise on the plant is considered. By 

 watering the aerial plant the same results were obtained as by water- 

 ing the roots, that is to say, the vital functions of the plant were 

 stimulated. But if large surfaces be placed in this way in contact 

 with a soluble salt of copper, the poisonous effects are felt more, and 

 leaf scald results from the too large quantities of salt absorbed. If 

 it be evident that the sulphuric acid of the blue vitriol, when liberated 

 by certain reactions, may exercise its well-known corrosive action on 

 the organs touched, the poisonous action of blue vitriol is especially 

 due to the copper which, absorbed by the leaves as sulphate of 

 copper, kills the cells of the organs traversed. These drawbacks still 

 occur, even with 0*1 per cent solutions. Owing to this annoying 

 effect sprayings with blue vitriol have been abandoned, and given 

 place to copper bouillies. The latter, which contain copper in an in- 

 soluble form, copper hydrate, or carbonate, produce on the leaves an 

 insoluble deposit, of which the latter can absorb the amount beneficial 

 to them. Thus there are realized on the leaves the conditions created 

 around the roots by spraying with blue vitriol. From the foregoing 

 it follows that blue vitriol is a violent poison to plants, and that its 

 contact, always injurious to the plant, should be avoided. Neither blue 

 vitriol, nor any of the other neutral salts of copper, is the suitable 

 copper compound to be applied to plants. The pollen of flowers 

 being very sensitive to the action of copper salts even when insoluble, 

 forbids their application during the flowering of the plant. Miani 

 found pollen to have the same sensitiveness as fungi spores, but that 

 an infinitesimal amount of copper salts stimulated their vitality. 



Action of Blue Vitriol on Algae and Saprophytic Fungi. — 

 Saprophytic fungi and algae behave to blue vitriol like phanerogamous 



