RECENT WORK IN AGRICULTURAL SCIENCE. 



CHEMISTRY. 



Acidimetry of phosphoric acid with the alkaline earths, J. Cavalier 



{Bui. Soc. Chilli. Parish, 3. ser., 25 {1901), No. 20-21, pp. 5tt?-.9ft5).— The author reports 

 the results of experiments from which he concludes that phosphoric acid may be 

 determined with sufficient accuracy l>y titrating with solutions of baryta, strontia, 

 or lime, using as indicator either methyl-orange or paranitrophenol, preferably the 

 former. With baryta water the concentration should not exceed 0.1 gram-molecule 

 per liter. If very great accuracy is required baryta water should be used and phenol- 

 phthalein sh-ould be employed as indicator, the operation being conducted in such a 

 manner as to give a crystalline precipitate. This may be obtained with solutions of 

 various strengths, either hot or cold. With a concentrated solution the operation is 

 more rapid when the liquid is heated. The change of color in this case is produced 

 by the addition of 1 molecule of barium (BaO) to 1 molecule of phosphoric acid 

 (H3PO4). For practical purposes baryta may be replaced by strontia, but only in 

 concentrated solution. It can not be replaced by dilute strontia nor by limewater. 

 When the precipitate is not perfectly crystalline the change of color of phenolphtha- 

 lein is always progressive and uncertain. Under such conditions this indicator can 

 not be used with baryta and strontia, since the results obtained with it are very vari- 

 able, depending upon the stirring, dilution, and duration of the experiment, the 

 amount of base required to cause change of color varying from 1 to 1.5 molecules. 

 With lime the amount is higher and more constant. In dilute solutions (0.01 gram- 

 molecule per liter) the change of color is produced quite regularly by the addition of 

 about 1.5 molecules of base. 



The determination of phosphoric acid in phosphates, J. A. Muller {Bui. 

 Soc. Chiin. Paris, 3. ser., 2.5 {1901), No. 23, pp. 1000-1002).— For the standardization 

 of the uranium solution used for the volumetric determination of phosphoric acid 

 the author recommends acid sodium ammonium phosphate ( HNaNH4P04.4H20) 

 as nuich more stable, and thus giving more accurate results than the ordinary cr3'^s- 

 tallized sodium phosphate, which loses water rea<lily. Crystallized dicalcium phos- 

 phate is also recommended for the same purpose, and a method for preparing this 

 substance in pure form is described as follows: To a dilute solution of pure calcium 

 chlorid add little by little a dilute cold solution of disodium phosphate until precipi- 

 tation is complete, collect on a filter, wash, and dry in thin layers at 70° C. Analy- 

 ses of the product so obtained l)y the molybdic and citric acid methods are reported. 

 The first method gave 41.45 and 41.38 per cent, the second 41.55 and 41.29 per cent 

 of phosphoric acid. It is claimed that the ammonium magnesium precipitate 

 obtained by the first method contains a little lime that yielded by the second a little 

 molybdic acid. The removal of these by dissolving and reprecipitating is described. 



The artificial preparation of monetite (dicalcium phosphate), A. ue Schul- 

 TEN {Bul. Soc. Min., 24 {1901), p. 323; abs. in Bui. Soc. Chim. Paris, 3. ser., 25 {1901), 

 No. 23, p. 1008). — This salt in pure and crystalline form is obtained by the slow 

 action of hot nitric acid on a hydrochloric-acid solution of calcium phosphate. 

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