CONVENTION OF OFFICIAL AGRICULTURAL CHEMISTS. 405 



adulterable food materials upon the market ... (2) by taking steps 

 to secure the establishment of standards of composition for pure food 

 substances." 



A committee consisting of A. L. Winton and B. W. Kilgore was 

 appointed to wait upon the Secretary of Agriculture and invite him to 

 attend the meetings of the Association. The Secretary accepted the 

 invitation and made a short address, commending the work of the 

 Association and citing a number of illustrations of the benefits which 

 practical agriculture has derived from chemical investigation. 



The usual committee on recommendations of reporters was appointed 

 as follows: J. M. Bartlett, H. J.Wheeler, M. A. Scovell, L. L.Van Slyke, 

 and B. H. Hite. 



FERTILIZERS. 



Phosphoric acid. — The report on phosphoric acid was presented by 

 H. B. McDonnell. The subjects of investigation during the past year 

 treated in this report were (1) comparative tests by 19 analysts of the 

 official molybdic method, the Pemberton 1 volumetric method as mod- 

 ified by Kilgore 2 and McDonnell 3 (the reporter) and Cladding's 4 method 

 on South Carolina and Florida rock phosphates, aluminum phosphate, 

 Pottstown slag, and cotton -seed meal; (2) comparative determinations 

 by 4 analysts of iron and aluminum in South Carolina and Florida 

 phosphates, slag, and a mixture of 1 part of ferrous ammonium alum, 

 1 of aluminum sulphate, and 2 of tricalcium phosphate, by the acetate, 

 thiosulphate, and Glaser methods (the Gladding"' potash method was 

 incidentally tested on mixtures of known composition) : (3) tests of solu- 

 bility of the phosphoric acid of slag (a) by the official method (digest- 

 ing for i and 1 hour), (6) in 1 per cent citric acid (digesting 1 gm. in 

 100 cc. of acid at 20° C. for 1 and 2 hours), and (c) by the Wagner 

 method; (4) fineness of slag as determined by passing 10 gm. through 

 a brass sieve with circular holes £ mm. in diameter and bolting cloth 

 with 4 and 5 meshes per millimeter; and (5) the determination of the 

 amount of slag removed by a magnet. 



The official method in its present form appeared to give entirely 

 satisfactory results; but the results by the volumetric method were not 



1 Jour. Amer. Cheni. Soc, 15 (1893), p. 382. 



2 U. S. Dept. Agr., Division of Chemistry Bui. 46, p. 13. Jour. Amer. (hem. Soc, 

 16 (1894), p. 765; 17 (1895), p. 950; 19 (1897), p. 703. North Carolina Sta. Bui. 140. 



'McDonnell's method is as follows: To an aliquot portion of the solution prepared 

 according to one of the official methods is added NH 4 OH in excess, then HN0 3 in 

 excess, then the regular raolyhdate solution (which should he filtered if necessary) 

 in excess. Warm on the water hath to about 50° C. for 20 or 30 minutes, with occa- 

 sional stirring, filter, wash -with water at ordinary temperatiire until filtrate fails 

 to show acidity when tested with litmus paper. Transfer the filter and contents to 

 a beaker, add 20 to 40 cc. of water and standard alkali sufficient to dissolve, stirring 

 well, titrate excess of alkali with standard sulphuric or nitric acid, using phenol- 

 phthalein as indicator. 



4 Jour. Amer. Chem. Soc, 18 (1896), p. 23. 



5 Ibid., p. 721. 



