ISOLATION, PURIFICATION, NUTRITION 41 



ing the minimum concentration of each element for the optimum 

 growth of Coccochloris Peniocystis would have the following 

 composition in ppm.: nitrogen, 13.6; phosphorus, 0.45; sulfur, 

 0.83; potassium, 2.25; magnesium, 0.13; iron, 0.03; and only traces 

 of calcium derived from the inoculum and from impurities in the 

 nutrients. When such a solution was tested, the yield was 91.5 

 mg. as compared with 109.7 ^^g- ^^^ ^^^ ^^^^^ solution with triple 

 nitrate concentration, and with double the minimum concentra- 

 tion of each element the yield was 11 8.2 mg. It is evident, there- 

 fore, that, whereas some adjustment of the nutrient solution may 

 be necessary for determination of the exact minimum require- 

 ments for maximum growth, the procedure followed above gives 

 a very close indication of the actual proportions in which the 

 elements are required under the conditions of these experiments. 



Comparison of Ferric Chloride and Ferric Citrate ■ 

 AS AN Iron Source 



When the present work on the isolation of the blue-green 

 algae was first started, a stock solution of ferric chloride was pre- 

 pared and used continuously as a source of iron in Chu No. 10 

 solution. It was soon found, however, that the algae made better 

 growth with fresh ferric citrate as an iron source. It was later 

 thought that possibly the ferric chloride solution became unsatis- 

 factory upon standing due to a slow conversion of the iron into 

 a form unavailable to the algae. Therefore, the experiment re- 

 ported in Table 6 was carried out to compare freshly dissolved 

 ferric chloride and ferric citrate plus citric acid and a twenty- 

 month-old ferric chloride solution as sources of iron for Cocco- 

 chloris Peniocystis. 



The data in Table 6 show that at high concentrations of iron, 

 1. 12, 0.56, and even 0.14 ppm., the fresh ferric chloride and ferric 

 citrate are equally effective. At the lower concentrations, 0.06 and 

 0.03 ppm., however, the ferric citrate produced greater yields. 

 At all concentrations, the twenty-month-old ferric chloride solu- 

 tion produced less growth than the fresh ferric chloride or ferric 

 citrate, showing that a stock solution of ferric chloride cannot 



