RECENT WORK I\ ACRICUETURAE SCIENCE. 



CHEMISTRY. 



The determination of phosphoric acid by means of ammonium phospho- 

 molybdate, (J. T. Baxter {Amer. Cliein. Jour., ,.'S {1903), No. 4, pp- '298-315, 

 fig_ jy — The author re])ort.s a study of the conditions of precipitation in which he 

 found that a jn-ecipitate of constant composition, (NH4):,P()4l2I\Ior)., can be 

 o))tained which contains o.78l^ per cent of phosjOioric acid. The i>h(>si)liate solution 

 (witliout large excess of nitric acid) should contain 0.1 gni. phosphoric acid to 50 cc, 

 and should be poured into at least 50 cc. excess of molybdic solution (150 gm. 

 ammonium-molybdate, 1 liter water, 1 liter nitric acid of 1.2 sp. gr. ) with vigorous 

 stirring, the mixture Ijeing allowed to stand at room temperature for 16 hours. The 

 preci})itate is washed with 10 per cent ammonium nitrate solution and heated in a 

 Gooch crucible at least 2 hours at 300° C. A curve is given from which the phos- 

 phoric-acid content for different weights of precipitate may l)e obtained. Precipita- 

 tion may be hastened by the addition of ammonium nitrate (10 gm. to 100 cc. of 

 molybdic solution) without api)reciab]y affecting the results. 



Determination of phosphoric acid in Wiborgh phosphate, M. Weikull 

 (Svensk Kern. T'uhkr., U {1902), p. 135; ahs. in Chem. Zt(/., 26 {1902), No. 90, EeperL, 

 p. 297) . — The citrate metliod was found to give too high results, due to simultaneous 

 precipitation of silicic acid. This was prevented by adding to the solution before 

 precipitation with magnesia mixture a 20 jter cent iron chlorid solution at the rate of 

 0.1 gm. of iron to 0.5 gm. of substance, and 2 drops of bromin water if the solution 

 smells of hydrogen sulphid. 



Methods for the determination of total phosphoric acid and potash in 

 soils, C. B. WiLLi.\MS (J?>.v. in Science, n. ser., 17 {1903), No. 418, p. ^P).— The 

 method proposed for phosphoric acid is as follows: After igniting 5 gm. of soil in a 

 platinum dish, treat 3 times with hydrofluoric acid, evaporating to dryness each 

 time. Fuse with 10 gm. of a mixture of equal parts of sodium and potassium car- 

 bonate, and after cooling the cake thus obtained transfer it to a beaker and digest 

 with 30 to 40 cc. of (1 to 1 ) hydrochloric acid. Evaporate the solution to dryness 

 on a water bath, heating subsequently for 4 or 5 hours in an air bath to 110° C. to 

 dehydrate silica. Take up in dilute hydrochloric acid, filter, and wash. Add suf- 

 ficient nitric acid to the mixed filtrate and washings thus obtained to liberate all 

 hydrochloric acid j)resent and evaporate to a volume of 40 cc. Neutralize the excess 

 of nitric acid with ammonia and add 10 to 12 gm. of ammonium nitrate. After cool- 

 ing add 30 cc. of recently filteretl molybdic solution, comi)leting the i)recipitatir)n by 

 the use of a Wagner shaking machine, and determine phosphoric acid volumetrically 

 by the author's method. « 



To determine total potash treat 4 gm. of soil in a platinum dish on a water bath, 

 after saturating with dilute (1 to 1) sulphuric acid and igniting, with from 2 to 3 cc. 

 of hydrofluoric acid, 5 times, adding 1 cc. of dilute (1 to 1) sulphuric acid just 

 before bringing to dryness the last time. . After the last traces of hydrofluoric acid 



«Jour. Amer. Chem. Soc.,23 (1901), p. 8. 

 630 



