SOILS— FERTILIZEES. 519 



field are considered to be poor, attention is called to the fact that there is 

 probably at least 5,000,000 tons of 60 per cent phosphate still available which 

 improved machinery may at some later time render workable. The highest 

 grade of rock that the field can be expected to produce, however, does not 

 average more than 61 per cent phosphate containing, as a rule, more than 

 3 per cent iron and alumina. 



A briefer report on these deposits has been noted (E. S. R., 30, p. 27). 



Solubility of the different constituents of slag, M. Sirot and G. Joret 

 (Jour. Agr. Prat., n. ser., 27 (WW, No. 25, p. 787; ahs. in Chem. Ahs., 9 {1915), 

 No. 5, p. 6SJf). — It is shown that citric and malic acids have greater solvent power 

 for the constituents of basic slag than do tartaric, acetic, lactic, and oxalic 

 acids. All of the constituents of the slag, including silicon, phosphoric acid, 

 calcium, magnesium, sulphates, iron, and manganese, were found to be soluble 

 in the weak acids, the solubility varying with the fineness of the slag and the 

 actual solubility of the salts formed. The author concludes that slag is not 

 simply a phosphatic fertilizer but that it contains many other substances useful 

 to plants in forms very soluble in weak organic acids. 



The solubility and assimilability by plants of the water insoluble-phos- 

 phoric acid or superphosphate prepared from Kostroma phosphates, P. Kos- 

 soviCH (Zhur. Opytn. Agron. {Russ. Jour. Expt. Land-io.), 15 (1914), No. 6, pp. 

 501-538, figs. 5). — Superphosphate containing about 11 per cent of phosphoric 

 acid soluble in water and 3i per cent almost completely soluble In Peterman's 

 reagent (ammonium citrate) made from low-grade phosphate (containing from 

 20 to 21 per cent of phosphoric acid) was tested in pot exi^eriments with oats 

 and mustard on sand and chernozem soil. The citrate-soluble phosphoric acid 

 appeared to be not less than half as valuable as the water-soluble for fertilizing 

 purposes. 



A new theory regarding the feeding power of plants, E. Truog (Science, 

 n. ser., 1^1 (1915), No. 1060, pp. 616-618). — As a result of his own investigations 

 and these of others, the author formulates the hypothesis that " plants contain- 

 ing a relatively high calcium oxid content have a relatively high feeding power 

 for the phosphorus in raw rock phosphate. For plants containing a relatively 

 low calcium oxid content the converse of the above is true." 



Within the meaning of this hypothesis " a calcium oxid content of less than 

 1 per cent may be considered relatively low. Corn, oats, rye, wheat, and millet 

 belong to this class. A calcium oxid content of somewhat more than 1 per cent 

 may be considered relatively high. Peas, clover, alfalfa, buckwheat, and most 

 of the species of the Crucif erse belong to this class." 



The exi^lanation offered for this hypothesis is that, with plants having a high 

 capacity for assimilating lime, the calcium bicarbonate formed by the action of 

 carbonic acid on tricalcium phosphate will be readily absorbed along with the 

 dicalcium form and thus permit the continued action of the carbonic acid on the 

 insoluble phosphate. On the other hand, with plants having a low assimila- 

 tive power for lime, the reaction between carbonic acid and tricalcium phos- 

 phate soon reaches a state of equilibrium, and soluble phosi^hate ceases to be 

 produced. The hypothesis is based upon the general theorem that the feeding 

 power of a plant for an insoluble substance depends "(1) on the solubility of 

 that substance in carbonated water and (2) on whether or not the plant removes 

 from solution all the products of the solubility reaction in the proper proportion 

 so as to allow the solubility reaction to continue indefinitely." 



Chlorosis of sugar cane, P. L. Gile and J. O. Carrero (Porto Rico Sta. Bpt. 

 191Jf, pp. IJf, 15). — Tests on the effect of ferrous sulphate and stable manure on 

 the development of chlorotic cane showed that small applications of these mate- 



