514 EXPERIMENT STATION RECORD. 



{1912), No. 3->,, pp. 129-216, pi. 1; abs. in Ztsclir. Angew. Chem., 25 {1912), No. 

 40, p. 2085). — Tbe author reviews the literature bearing on this subject and 

 reports pot experiments with oats and peas grown on sand and on freshly 

 crushed sandstone of different kinds. It was found that the cementing material 

 of the sandstones contained readily available plant food, which is largely lost 

 during weathering, as illustrated by the results with sand, which is the extreme 

 product of the weathering process. 



Acid excretion of roots and the solubility of plant food constituents of 

 the soil in water solutions of carbon dioxid, T. Pfeiffer and E. BlancB. 

 {Landic. Vers. Stat., 77 {1912), No. 3-4, pp. 2i7-26S).— The authors critically 

 review the woa-k of other investigators on this subject and report the results of 

 experiments on the assimilation of phosphoric acid from monocalcium phos- 

 phate and different phosphorites by oats, lupines, and peas, grown in pots, the 

 soil in which was kept charged with carbon dioxid. The carbon dioxid was 

 conducted under pressure into the soil through the ventilation tubes of the 

 pots. The soil was completely saturated in this way three times a week. The 

 water content of the soil was maintained at 10 per cent during the exj[3eriment. 



The results showed that addition of carbon dioxid gave favorable results 

 only with the easily soluble phosphates. The phosphorites required stronger 

 acid solvents to render them available to plants. It was also observed that the 

 assimilation of phosphoric acid was greater for the legumes than for oats. 

 The addition of carbon dioxid did not offset this difference. 



The general conclusion, therefore, is that the assimilative power of plant 

 roots is not dependent alone upon the carbon dioxid given off, but that other 

 organic acids play an important rule. 



The action of different solvents on the plant-food constituents of the 

 soil, O. Engels {Landw. Vers. Stat., 77 {1912), No. 3-4, pp. 269-304; abs. in 

 Chem. Abs., 6 {1912), No. 14, pp. 1948, 1949). — The author reviews previous 

 investigations on the subject by others and reports results of studies of the 

 relative solubility of phosphoric acid, potash, and lime of soils in 10 per cent 

 hydrochloric acid, 2 per cent citric acid, water solutions of carbon dioxid, and 

 distilled water, using four dift'erent soil types ranging from light sands to 

 heavy clays. In order to determine the solubility of the plant-food constitu- 

 ents in the original, as distinguished from the absorbed state, the experiments 

 were made (1) on the untreated soil and (2) after treatment with 18 per cent 

 solutions of superphosphate and potassium sulphate. 



It was found that, although the solubility of the plant-food constituents 

 varied, there was a uniformity in the action of the solvents. The absorption 

 of phosphoric acid and of potash also varied for the different soils, being higher 

 for the heavy clay soils, which contained also the higher lime, iron oxid, and 

 alumina contents, and decreasing for loess loam and sandy soils in the order 

 named. The solubility of the absorbed phosphoric acid was much higher for 

 the lighter soils with low lime content. This was also true for the solubility 

 of the potash, although the difference in solubility was not so pronounced. 



The solubility of phosphoric acid and potash in the water solutions of car- 

 bon dioxid was substantially greater than that in water, being twice as great 

 in the case of phosphoric acid and increasing in the case of potash in sandy soil 

 from 34.08 to 55.08 per cent. The difference was less marked in the heavier 

 soils. 



The 2 per cent solution of citric acid dissolved substantially all the absorbed 

 phosphoric acid and 90 per cent of the i)otash in case of sandy soils, whereas 

 with the three heavier soils considerable amounts of the phosphoric acid and 

 about one-third of the potash remained fixed in the soil. 



