1917] AGRICULTURAL CHEMISTRY — AGROTECHNY. 613 



It is iudicated that a comparison of results witli similar soils is useful, but 

 that a comparison of dissimilar soils would involve difficulties. The proper way 

 to use a soil analysis is in conjunction with a soil survey. 



A diffusion method in which the reverse reaction is eliminated during acid 

 extraction, thus yielding a true measure of the direct solubility action, is de- 

 scribed. 



Notes on the nature of the phosphates contained in mineral phosphates, 

 G. S. Robertson (Jour. Agr. Sci. [EnglaJid], 8 (1916), No. 1, pp. 16-25, figs. 2).— 

 The results obtained from the examination of five different mineral phosphates 

 indicate the presence of three distinct compounds of phosphoric acid and cal- 

 cium oxid. The formulas of the compounds are submitted. 



It was found that the substitution of fluorin or chlorin for the oxygen of one 

 of the CaO groups in the rock phosphates examined did not interfere with the 

 ratio PaOs : CaO. It is indicated that the combination of fluorin or chlorin 

 in this manner would account for the low solubility of rock phosphates in citric 

 acid as compared with bone meal, while the higher lime content of the phos- 

 phates would account for their higher solubility in citric acid as compared 

 with apatite. " The results of calcining the various mineral phosphates show 

 that a citric-soluble silica phosphate is formed. This phosphate goes into solu- 

 tion in the first citric extract. In addition to the silica phosphate one or more 

 phosphates with a lower lime content than the original phosphate are produced 

 by calcining. The longer the calcining continues the greater is the tendency 

 to produce phosphates of low lime content, and hence the lower the solubility." 



It is further noted that the higher the percentage of lime actually combined 

 with phosphoric acid, the more soluble the mineral phosphate is in citric acid. 



Note on the loss of phosphoric acid during fusion with ammonium fluorid, 

 W. A. Davis and J. A. Pbescott (Jour. Agr. Sci. lEngland], 8 (1916), No. 1, pp. 

 136-138). — Experiments with sodium acid phosphate, potassium diacid phos- 

 phate, calcium phosphate, and apatite have shown that on ignition with am- 

 monium fluorid a considerable loss of pho.sphoric acid may occur. The loss is 

 least in the case of salts containing an alkali metal, and greatest in the case 

 of phosphates of the alkaline earth metals, as calcium phosphate or apatite. 

 It is indicated that the phosphorus is probably volatilized in the form of phos- 

 phorus fluorid. 



Estimation of calcium in ash of forage plants and animal carcasses, S. B. 

 KuziBiAN (Iowa Sta. Research Bui. 32 (1916), pp. 99-110).— The following 

 modified procedure is proposed : 



The filtrate (acid with nitric acid) from the precipitation of phosphorus as 

 ammonium phosphomolybdate is made ammoniacal and an excess of ammonium 

 oxalate added. The solution is brought to boiling and kept so for 30 minutes, 

 set aside for two hours, and filtered through a Gooch crucible. The precipi- 

 tate is ignited to convert the oxalates into oxids and cooled rather rapidly by 

 allowing to stand in the air. The contents are then carefully moistened with 

 water over a beaker and dissolved in dilute hydrochloric acid. The contents 

 of the crucible, together with the asbestos, are carefully washed into the 

 beaker, the latter is covered with a watch glass and gently warmed on a water 

 bath or hot plate, and after complete solution filtered through ashless paper and 

 the asbestos carefully washed. Ammonium chlorid is added, and the solution 

 made ammoniacal and boiled for a few minutes until the odor of ammonia be- 

 comes faint. The precipitated iron and aluminum are removed by filtration, the 

 filtrate heated to boiling, "and the calcium precipitated as oxalate. The calcium 

 is entirely free from molybdenum salts at this stage of the process. 



