RECENT WORK IN AGRICULTURAL SCIENCE. 



AGRICULTURAL CHEMISTRY. 



On the determination of water-soluble and total phosphoric acid in super- 

 phosphates, K. Roiiii {C/icm. Ztg., 30 {1006), No. J/Ji, pp. 5Ji2, oJ/.J ; aba. in 

 .ijuili/st. .11 (I'.tOC), Ao. J«.>. p. 215; .Jour. C'Jieni. *S'oc. [London], 90 (1906), 

 Xo. .525, II, p. -'lOO; Chcni. Centhl, 1906, 11, No. 2, p. 163).— " Water- fioluble 

 phosphoric acid. — A iiuuiber of determinations were made on 3 samples to 

 compare tlie method in which the sample is digested with water for 2 hours, 

 with occasional shalang, with that in which it is agitated continuously witli 

 water for 30 minutes in a shaking machine, different speeds being also tested. 

 The most constant results are given by the latter method, the speed being 

 about 30 to 40 rotations per minute, but digesting the sample without any 

 shaking at all gave results only about 0.2 per cent too low (with 19 per 

 cent of water-soluble P2O5). The sample used should pass through a 2 mm. 

 mesh sieve. 



"7'o/«/ phosjihoric (tcid. — Extraction with nitric acid, with a mixture of nitric 

 and sulpliuric acids, and with aipia regia, gave practically identical results. 

 Extraction with hydrochloric acid, which is never used in practice, gave results 

 about 0.2 per cent too low. The magnesia precipitate should be allowed to 

 stand 24 hours before filtering, or else mechanically stirred for 30 minutes. 

 On allowing it to stand for only 2 hours, an error of up to 0.22 per cent of P2O5 

 was found in a number of analyses." 



Investigations on the causes of error in the a^jplication of the citro- 

 niechanical method to the determination of phosphoric acid in natural 

 IDhosphates and phosphatic slags, E. (Juerky and E. Toussaint (BiiI. Aijr. 

 IBru.s.scls], 22 {1906), No. 3, pp. 315-3-'t9 ; Bui. Soc. Chiin. Self/., 20 (1906),' No. 

 ■'>-6, pp. 167-203). — Studies are reported which lead to the conclusion that the 

 errors referred to are due to the presence of fluo-silicates and to a deficiency of 

 iron salts as compared with silica in solution. Th(> author proposes to eliminate 

 llie eri-ors due to these causes by removing the fmorin by treatment with sul- 

 I)huric acid and by adding iron salts before precipitation according to the fol- 

 lowing method : 



To 2.5 gm. of the material in a 250 cc. Jena glass flask add 10 cc. of concen- 

 trated sulphuric acid and heat over wire gauze until acid fumes begin to appear, 

 allow to cool, adding water carefully until the volume has reached about 100 

 (C, then add 25 cc. of aqua regia and boil for 10 minutes on a sand bath, cool, 

 make the volume to 250 cc., and filter. To 25 cc. of tlie filtrate add in the case 

 of natural phosphates 5 to 10 cc. of a 2 per cent solution of ferric chlorid, 

 neutralize partially with ammonia, cool if necessary, and add 30 cc. of citrate 

 solution with 15 cc. of annnonia and .35 cc. of magnesia mixture, shake for i 

 hour, filter after allowing to stand for 1 hour. wash, ignite, and weigli. 



The author uses either Peterman's alkaline citrate or a solution containing 

 500 gm. of citric acid neutralized with a slight excess of ammonia and made to 



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