248 



SCIENCE 



[N. S. Vol. XLIV. No. 1129 



rock phosphate and in mixtures of soil and raw 

 rock phosphate. 



SOLUTION OF PHOSPHATES BY ACTION" OF NITRITE 

 BACTERIA 



To determine the part played by the nitrite 

 bacteria in dissolving mineral compounds, and 

 particularly raw rock phosphate, was our prin- 

 cipal object in these experiments. 



One of the authors made the following sug- 

 gestion several years ago : 3 



In the conversion of sufficient organic nitrogen 

 into nitrate nitrogen for a hundred-bushel crop of 

 corn, the nitric acid, if formed, would be alone 

 sufficient to convert seven times as much insoluble 

 tricalcium phosphate into soluble monocalcium 

 phosphate as would be required to supply the 

 phosphorus for the same crop. 



The plan of the experiment, briefly stated, 

 was as follows: A thin layer (about £ inch 

 thick) of a nutrient salt solution was placed in 

 a cone-shaped glass flask of about one liter 

 capacity and about 5 inches in diameter at 

 the bottom. In this solution was placed a defi- 

 nite amount of ammonium salt. The flasks 

 and materials were carefully sterilized. Nitrite 

 bacteria were introduced from pure cultures 

 and sometimes directly from soil. The flasks 

 were plugged with cotton kept at a tempera- 

 ture of 28° C. Many such flasks were pre- 

 pared, and later, usually at intervals of one 

 week, the contents of two or more flasks were 

 analyzed for nitrogen changed or oxidized and 

 for water-soluble phosphorus and calcium. 



In Table I. are shown the relative amounts, 

 by weight, of nitrogen from ammonia sulfate 

 oxidized to nitrite by nitrite bacteria and the 

 amounts of phosphorus and calcium made 

 soluble. Each figure represents the average of 

 duplicate determinations. 



EXPLANATION OF RESULTS 



The results reported in Table I. demonstrate 

 conclusively that phosphorus and calcium are 

 made soluble while the nitrite bacteria oxidize 

 ammonia nitrogen to nitrite nitrogen. It is 

 also evident that the solubility increases with 

 increasing time of action of the bacteria. 



3 Hopkins, ' ' Soil Fertility and Permanent Agri- 

 culture," 197. 



TABLE I 



Phosphorus, Calcium, and Nitrogen Required by 

 Crops, Compared with that Possible of So- 

 lution when Nitrite Bacteria Act upon 

 Tricalcium Phosphate 

 (Expressed in Pounds) 



Corn: 



Grain, 100 bu.; Stover, 3 tons: 



cobs, }4 ton 



Wheat: 



Grain, 50 bu. ; straw, 2}^ tons . . 

 Oats: 



Grain, 100 bu.; straw, 2}4 tons. 

 Timotlvy, 3 tons 



321 



206 



208 

 163 



An inspection of the figures shows that 

 there is, by weight, approximately twice as 

 much phosphorus and four times as much cal- 

 cium made soluble as there is nitrogen oxidized 

 by the bacteria. As an average of the results 

 from thirteen flasks (]STos. 4 to 16), we find 

 that from the oxidation of 56 pounds of nitro- 

 gen 115 pounds of phosphorus and 211 pounds 

 of calcium are made soluble. (The results 

 from Flasks 1, 2 and 3 are not included in the 

 ratio calculated.) According to theory, when 

 56 pounds of nitrogen are changed from the 

 ammonia form to the nitrite form, with both 

 the nitrous acid (UNO,) and the associated 

 sulfuric acid (H.SO,) acting on the pure rock 

 phosphate, 124 pounds of phosphorus and 240 

 pounds of calcium are made soluble. 



Ten cubic centimeters of Flask 16 required 

 3.35 cc. of N/12.5 ISTaOH with phenolphthalein 

 as the indicator for the second hydrogen atom. 

 The normality of the solution was found to be 

 jST/37.2. 



importance and extent of the action of 

 nitrite bacteria 



It has already been shown that the nitrite 

 bacteria make phosphorus and calcium soluble 

 from pure rock phosphate and that the action 

 conforms to a definite chemical ratio. 4 



4 It was found that the action of the nitrite 

 bacteria was the same on the natural raw rock 



