138 EXPERIMENTS WITH SULPHATE OF IRON. 



have not been published.* The same salt has also been tried 

 by Mr Griss, as an application to diseased potatoes, and by 

 Mr Gandry, to diseased fruit-trees ; and in both cases, it is 

 said, with decided success. 



This salt, when exposed to the air, either in the state of 

 crystals or of solution in water, is decomposed, becomes covered 

 with a yellow ochre, and acquires acid properties. It may be 

 doubted, therefore, whether the iron it contains, though to a 

 certain extent necessary to the plant, exercises any real influence 

 upon its growth. It is worthy of experimental investigation, 

 however, 



1. What is the effect of this sulphate compared with that of 

 an equivalent quantity of sulphuric acid? (See above, chap. 

 vi. 2.) 



2. What is its effect on the appearance and produce of 

 plants compared with those of the sulphates of so da and magnesia, 

 which are equally soluble in water? 



3. What are its special effects on different plants, when 

 applied at different seasons ? 



4. Has it any beneficial action upon sickly or diseased 

 plants, when applied either as a top-dressing or in a state of 

 solution to the roots ? 



It will be safer to commence with applications not exceeding 

 1 cwt. to the imperial acre. 



* An account of the French experiments appeared in the Annales de Chem. 

 et de Phys., but as I omitted to note down the reference, I am at present unable 

 to discover in what volume they are to be found. 



