626 EXPERIMENT STATION EECOED. [Vol. 36 



tity representing the potash from highly insoluble compounds. Additions of 

 sulphate of lime, nitrate of soda, or other salts have no such effect upon ren- 

 dering potash available to plants as has been claimed. They would have only 

 a slight effect." 



A study of conditions affecting the yield of sugar humus is also reported and 

 a method of preparing it described. 



Solubility of mineral phosphates, A. Aita {Ann. Ghim. Appl. [Rome], 6 

 {1916), No. 1-2, pp. 28-U, fig- 1; abs. m Ghern. Ahs., 10 {1916), No. 22, pp. 

 2953. 2954). — Consecutive extractions with 2 per cent citric acid made on dif- 

 ferent types of phosphates showed that nodulous and hard phosphates gave 

 up their phosphoric acid more slowly than the more friable varieties, seven or 

 eight extractions being required for the former. 



With reference to the influence of the calcium oxid content, it was found 

 that in the first extraction the percentage of phosphoric acid extracted increased 

 as the calcium oxid content decreased. In the successive extractions the per- 

 centage of phosphoric acid extracted continually increased in the case of high 

 calcium oxid content, with the order of the extraction as the calcium oxid dis- 

 appeared under the action of the citric acid. With phosphate of low calcium 

 oxid content the opposite occurred in subsequent extractions. Ignited phos- 

 phates gave up their phosphoric acid more slowly than the natural minerals. 



In studies of the solubility of mineral phosphates in 2 per cent citric acid 

 in the presence of salts, two consecutive extractions were made. It was found 

 that (1) calcium salts diminished the solubility, (2) ammonium, alkali, and 

 magnesium salts brought about an increase of solubility proportionate to their 

 concentration and dependent on the factors of friability, fineness, and calcium 

 oxid content, and (3) the increase of solubility was a function of the anion. 

 The author attempts to explain these results, and draws the conclusion that 

 finely ground mineral phosphates may be used in agricultural practice as 

 substitutes for basic phosphates if they are accompanied either at the time of 

 spreading over the soil or during growth of the vegetation by fertilizers of 

 ammonium, potassium, or soluble magnesium salts. 



The utilization of phosphates by agricultural crops, including a new 

 theory regarding the feeding power of plants, E. Tkuog {Wisconsin Sta. Re- 

 search Bui. 41 {1916), pp. 50, figs. H). — Supplementing experiments previously 

 reported (E. S. R., 27, p. 127), pot culture experiments were made with corn, 

 oats, barley, millet, turnips, rape, buckwheat, clover, alfalfa, serradella, sun- 

 flowers, and tobacco to test the availability of acid phosphate, rock phosphate, 

 ferrous phosphate, ferric phosphate, tricalcium phosphate, aluminum phos- 

 phate, manganous phosphate, and trimagnesium phosphate. In the case of corn 

 the effect of different nitrogenous compounds, namely, calcium, ammonium, 

 sodium, and potassium nitrates, was also tested. The degree of utilization 

 of the phosphates was measured both by the yield and the phosphorus content 

 of the crops grown. 



It was found that " the different species of plants showed some marked 

 individual preferences for the different phosphates. Solubility of the phos- 

 phates was not the only factor that determined the growth of a plant on 

 these phosphates. Precipitated ferric and aluminum phosphates produced 

 with a few exceptions good growths and in a few cases even better growths 

 than the acid phosphate. The availability of these phosphates is undoubtedly 

 due to ease of hydrolysis of the neutral or nearly neutral material, in which 

 case the phosphoric acid goes into solution and there is left a basic phosphate. 

 . . . The phosphorus of precipitated tricalcium phosphate was much more 

 available than that of rock phosphate, although the form of phosphate is perhaps 

 nearly the same in the two." The author attributes this to the greater ease of 



