WATER-CULTURE METHOD HOAGLAND AND ARNON 487 



Grams dissolved in 1 liter 

 Compound: ofHiO 



H3BO3, boric acid 2. 86 



MnCl 2 .4H 2 0, manganese chloride 1. 81 



ZnS0 4 .7H 2 0, zinc sulphate . 22 



CuS04.5H 2 0, copper sulphate . 08 



H2M0O4.H2O molybdic acid (assaying 85 percent M0O3) . 09 



Add 1 cc of this solution for each liter of nutrient solution, when 

 solution is first prepared or subsequently changed, or at more frequent 

 intervals if necessary. 



This will give the following concentrations: 



Parts per million of nutrient 

 Element: solution 



Boron 0. 5 



Manganese . 5 



Zinc . 05 



Copper . 02 



Molybdenum . 05 



(6) Add iron in the form of 0.5 percent iron tartrate solution or 

 other suitable iron salt, at the rate of 1 cc per liter, about twice a week 

 or as indicated by appearance of plants. 



The reaction of the solution is adjusted to approximately pH6 by 

 adding 0.1 NH 2 S0 4 (or some other suitable dilution). 



Molar solutions. — The concentrations of stock solutions of nutrient 

 salts used in preparation of nutrient solutions are conveniently expressed 

 in terms of molarity. A molar solution is one containing a 1 gram- 

 molecule (mol) of dissolved substance in 1 liter of solution. (In all 

 nutrient-solution work, the solvent is water.) A gram-molecule or 

 mol of a compound is the number of grams corresponding to the 

 molecular weight. 



Example 1: How to make a molar solution of magnesium sulphate: 

 The molecular weight of magnesium sulphate, MgS0 4 .7H 2 is 264.50. 

 ODe mol of magnesium sulphate consists of 264.50 grams. Hence to 

 make a molar solution of magnesium sulphate, dissolve 264.50 grams 

 of MgS0 4 .7H 2 in water and make to 1 liter volume. 



Example 2: How to make a Ko molar (0.05 M) solution of mono- 

 calcium phosphate, Ca(H 2 P0 4 )2.H 2 0: The molecular weight of mono- 

 calcium phosphate, Ca(H 2 P0 4 ) 2 .H 2 is 252.17. Hence 0.05 mol of 



252 17 grams 

 Ca(H 2 P0 4 ) 2 .H 2 is '—^ =12.61 grams. Therefore, to make a 



0.05 M solution of monocalcium phosphate, dissolve 12.61 grams of 

 Ca(H 2 P0 4 ) 2 .H 2 in water and make to 1 liter volume. 



