Rothamsted Symposium on Trace Elements 16 



pared by the alkaline phosphate adsorption method devised by 

 Steinberg (1) adapted for large scale use by Stout and Arnon 

 (2) and further modified here to include sodium bicarbonate be- 

 fore heating, which markedly increases the adsorptive efficiency 

 of the reaction. Most reagents used for boron deficiency are 

 purified by two or three recrystallisations during each of which an 

 equal volume of purified alcohol is added to obtain economical 

 recoveries of over 90%. The first recrystallisation is carried out 

 in slightly acid solution to enhance the separation from boric acid 

 in the mother liquor. A pure calcium nitrate is prepared from 

 redistilled nitric acid and reprecipitated calcium carbonate. 



The basal reagents required for molybdenum deficiency are 

 first recrystallised as described above and then further purified by 

 a new method specially designed to remove this element. The 

 method is based on the use of 8 hydroxyquinoline for the concen- 

 tration of molybdenum and other elements by co-precipitation 

 with iron from ash solutions prior to spectrographic analysis (3). 

 As used here nearly all the 8 hydroxyquinoline is removed by the 

 addition of the calculated equivalent of iron as ferric chloride and 

 molybdenum is carried down when the iron compounds are pre- 

 cipitated by potassium hydroxide at pH 5.0. Higher values for 

 pH cause desorption of the molybdenum. Control experiments 

 have shown that this method does not produce toxic effects from 

 such traces of 8 hydroxyquinoline that may remain after pre- 

 cipitation. This method was devised as experiments showed that 

 the alkaline phosphate adsorption method does not satisfactorily 

 remove molybdenum. 



Iron compounds require special attention for trace element re- 

 search. When required for work on manganese problems the 

 ferric citrate used is prepared from ferric chloride freed from man- 

 ganese compounds by extraction with ether saturated with 6N. 

 hydrochloric acid (4), (5). As this method also concentrates 

 molybdenum compounds with the iron a different procedure is 

 used to obtain ferric citrate for molybdenum deficiency cultures. 

 Ferric chloride is first acidified with hydrochloric acid and shaken 

 with toluene 3:4 dithiol in amyl acetate which extracts molybde- 

 num. The iron in the ferric chloride is then partially precipi- 

 tated with 8 hydroxyquinoline and filtered; the residual iron is 

 precipitated as ferric hydroxide with ammonia and converted to 

 the citrate with recrystallised citric acid. 



