CONVENTION OF OFFICIAL AGRICULTURAL CHEMISTS. 273 



H. A. Huston presented a paper in which he discussed the ettect of 

 time, temperature of digestion, and rehitive proportions of substance 

 and of solvents upon the citrate solubility of phosphoric acid in slag. 

 The data were given in tabular form and in diagrams. It was shown 

 conclusively that the solution in the citrate is not complete in half an 

 hour, but with the particular sample used required 5 hours for its com- 

 ])letion. It was also shown that if sufficient time were given the tem- 

 perature of digestion had little intluence on the amount of i^hosphoric 

 acid dissolved. In connection with these tests it was incidentally ob- 

 served that the method prescribed by Wagner for the determination 

 of the basicity of slags is not reliable, as it does not give concordant 

 results. This paper furnished the text for a general discussion of the 

 unreliabihty of organic solvents in determining the availability of 

 phosphoric acid in different kinds of phosphates. It was clearly 

 brought out that tlie results obtained by the use of the various cit- 

 rate methods are wholly misleading in case of certain kinds of phos- 

 phates. 



A i)aper on "The amount of washing required to remove the phos- 

 phoric acid rendered soluble by digestion with ammonium citrate at 

 65° C." was presented by F; P. Veitch. Determinations were made of 

 the phosphoric acid in the second, third, fourth, and fifth washings of 

 the residue from digestion with citrate of ammonia in case of 15 fertil- 

 izers, with the following average results: In the second washing, 0.129 

 per cent; in the third, 0.053; in the fourth, 0.043; and in the fifth, 

 0.027. After washing the residue with 150 cc. of water the next 100 cc. 

 of washings was found to contain 0.051 per cent of phosphoric acid. 



A paper by T. S. Gladding, entitled "Discussion on the estimation 

 of phosphoric acid," was read by the secretary. It was shown in this 

 paper that in order to get accurate results in the volumetric method 

 lor phosphoric acid it is necessary to add the molybdic solution slowly 

 and to wash only 3 or 1 times with 20 cc. portions of wash water. If 

 the molybdic solution is added all at once the precipitate contains a 

 considerable amount of impurities. If the washing of the i^recipitate 

 is continued beyond the limits specified the phosphoric acid gradually 

 passes into solution, as was shown by a number of tests of the washings. 



The secretary of the Association, H. W. Wiley, submitted a paper 

 on "Mechanical analysis of basic phosphatic slag."' The slag was sep- 

 jirated into different grades by means of alcohol and the phosphoric 

 acid determined in each grade. A wide difference in phosphoric acid 

 content was shown, and the results suggest the advisability of manu- 

 facturers grading their ground slag by some such means before putting 

 it on the market. 



It developed in the discussion on methods for phosphoric acid that a 

 number of chemists had found ditliculty in getting concordant results 

 with the volumetric method, so it was not deemed advisable to make 

 this method official without further tests. The reporter was therefore 



