Preparation of the Solutions. 



Introduction. The Baker Chemical Company, of Phillipsburg, 

 N. J., has very kindly agreed to prepare the salts needed for 

 this cooperation in special lots, and at cost, so that all of any 

 given salt will be of the same lot. These salts will be put up in 

 sealed bottles with a label to indicate this project of the National 

 Research Council, and the analysis (including the mean water 

 content) will be shown on the label. These salts may be obtained 

 from the above-named manufacturers by specifying that they are 

 needed for the Plant Nutrition Project of the National Research 

 Council. At the outset of our work salts from othefr lots will 

 have to be used, since it will take some time for the various 

 laboratories in this cooperation to obtain the special salts. 

 Orders should" be placed as soon as possible, and it will help the 

 work if the committee is informed by sending to Baltimore a 

 memorandum of the salts ordered when the order is sent to the 

 manufacturer. Cooperators are asked to do this. 



The nutrient solutions are to be prepared by adding, in each 

 case, measured amounts of the single-salt stock solutions to a 

 measured amount of distilled water. The first operation is, con- 

 sequently, to make up the single-salt 'stock solutions. 



The Single-Salt Stock Solutions. These should be made up so 

 as to have the following volume-molecular concentrations. They 

 will keep for a long time and should be tightly stoppered and 

 preserved in darkness. 



The amount of salt to be used is weighed out and placed in dis- 

 tilled water in a volumetric flask or other suitable container, 

 being shaken from time to time until solution is complete after 

 which the solution is made up to required volume by adding water. 

 Heat may be applied to hasten solution in some cases, but it 

 would produce decomposition in others. It is best to dissolve all 

 salts at room temperature, excepting those noted below, for 

 which lower temperature is needed. 



The three phosphates should be dissolved at temperatures 

 below 20° C, and calcium sulphate would be dissolved at a 

 temperature below 15° C. Its solubility limit is lower with 



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