486 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 8 



(b) Zinc and copper solution. — Ordinarily this solution may be omit- 

 ted, because these elements will amost certainly be supplied as im- 

 purities in water or chemicals, or from the containers. When it is 

 needed additions are made as for solution a. To prepare solution 6, 

 dissolve 1 teaspoon of chemically pure copper sulphate (CuS0 4 .5H 2 0) 

 and 4 teaspoons of chemically pure zinc sulphate (ZnS0 4 .7H 2 0) in a 

 gallon of water. Dilute 1 part of this solution with 4 parts of water. 

 Use 1 teaspoon of the diluted solution for each 25 gallons of nutrient 

 solution. 



(c) Additions of iron to nutrient solution. — Generally, iron solution 

 will need to be added at frequent and regular intervals, for example, 

 once or twice a week. If the leaves of the plant tend to become 

 yellow, even more frequent additions may be required. However, a 

 yellowing or mottling of leaves can also arise from many other causes. 



The iron solution is prepared as follows: Dissolve 1 level teaspoon 

 of iron tartrate (iron citrate or iron sulphate can be substituted, but 

 the tartrate or citrate is often more effective than the sulphate) in 1 

 quart of water. Add % cup of this solution to 25 gallons of nutrient 

 solution each time iron is needed. 



PREPARATION OF NUTRIENT SOLUTIONS: METHOD B, FOR SCHOOLS OR 

 TECHNICAL LABORATORIES 



For experimental purposes, the use of distilled water and chemically 

 pure salts is recommended. Molar stock solutions (except when 

 otherwise indicated) are prepared for each salt, and the amounts indi- 

 cated below are used. 



Solution 1 Cubic centimeters in aliter of 



nutrient solution 



M KH2PO4, potassium acid phosphate 1 



M KNO3, potassium nitrate 5 



M Ca(N0 3 ) 2 , calcium nitrate 5 



M MgS0 4 , magnesium sulphate 2 



Solution 2 Cubic centimeters in a liter of 



nutrient solution 



M NH4H2PO4, ammonium acid phosphate 1 



M KNO3, potassium nitrate 6 



M Ca(N0 3 )2, calcium nitrate 4 



M MgS0 4 , magnesium sulphate 2 



To either of these solutions add the following solutions a and b 

 below. 



(a) Prepare a supplementary solution which will supply boron, 

 manganese, zinc, copper, and molybdenum as follows: 



