1918] AGRICULTURAL CHEMISTRY AGROTECHNY. 205 



has been devised and is described. The general procedure is to bring the ma- 

 terial to be analyzed into a solution containing in 100 cc. at least from 10 to 

 15 cc. concentrated sulphuric acid, 20 cc. of nitric acid or from 5 to 10 cc. of 

 sirupy phosphoric acid, or mixtures of two or more of the acids. The solution 

 must be previously freed from reducing agents by boiling with nitric acid, 

 adding a little persulphate if carbon compounds are present. If chlorids are 

 present the solution should be evaporated with nitric and sulphuric acids. 

 P'rom 0.2 to 0.4 gm. of potassium or sodium periodate is added, the solution 

 boiled for a minute, kept hot from five to ten minutes, cooled, diluted to the 

 proper volume, and compared with a standard of known manganese content, 

 similarly prepared. The solution, when ready to be compared, should not 

 contain much more than 1 mg. of manganese per 50 cc, as otherwise the color 

 would be too dark. In the presence of considerable iron either sulphuric or 

 phosphoric acid must be present, since the ferric periodate is insoluble in con- 

 centrated nitric acid but readily soluble in other acids. 



The method is indicated as being specially adapted for the determination of 

 manganese in water, soil, ores, and other materials in which it is present in 

 small amounts. 



An attempt to use the reaction as a basis of a volumetric method was un- 

 successful. 



A bibliography of 34 references to the literature on the colorimetric determi- 

 nation of manganese is appended. 



Some suggestions concerning the preparation of ammonium citrate solu- 

 tion and the determination of insoluble phosphoric acid, P. McG. Shuey 

 {Jour. Indus, and Engin. Chem., 9 (1917), No. 11, p. 10^5). — The author notes 

 that he has found that the neutral point in the preparation of ammonium 

 citrate by the addition of ammonium hydroxid to citric acid can be reached 

 at once by calculating the amount of ammonia required for a given amount of 

 citric acid according to the following equation : 



CsHiOH ( OOOH ) j+3NH3=C3H«OH ( COONH* ) ,. 



Practical examples of the preparation of ammonium citrate solution and 

 some notes on its use for determining soluble phosphoric acid in various ma- 

 terials are included. 



The determination of soil phosphorus, C. O. Rost {Soil Sci., It {1911), No. 4, 

 pp. 295-311). — In the study reported the author, at the Minnesota Experiment 

 Station, compared the fusion with sodium carbonate method, the Fischer and 

 Hilgard (E. S. R., 15, p. 746) methods, involving extraction with strong acid, 

 the Washington hydrofluoric acid method, a modification of Washington's 

 method proposed by Robinson (E. S. R., 34, p. 806), and a modification pro- 

 posed by himself for the determination of phosphorus in soils. The author's 

 modification of Washington's method provides for the elimination of the or- 

 ganic matter of soils and the complete extraction of the phosphorus by means 

 of hydrofluoric and nitric acids. The procedure is described in detail. 



The results of the comparative study show that only a negligible quantity 

 of phosphoric acid was recoverable from the separated silica with the fusion 

 method. Neither evaporation with magnesium nitrate previous to ignition nor 

 precipitation of the phosphoric acid with the sesquioxids of iron and aluminum 

 in order to separate it from the excess of sodium salts was found advantageous. 



" The Fischer method recovered practically all of the phosphoric acid in the 

 peat soils, but in most cases with minei-al soils a considerable amount was 

 left in the insoluble residue. None was lost by volatilization or rendered unre- 

 coverable by the formation of compounds of iron and aluminum insoluble in 

 44073°— 18 2 



