506 EXPERIMENT STATION RECORD. 



and allow the silver chlorid to settle. Decant a small portion of the 

 supernatant liquid into a test tube. Test one portion of this for chlorin 

 with a small crystal of silver nitrate and the other for silver with hydro- 

 chloric acid or ammonium chlorid. If an excess of silver is shown, 

 collect the silver chlorid precipitate on a filter, dry, and weigh in the 

 usual manner. 



Phosphoric acid. — The referee on phosphoric acid, B. W. Kilgore, 

 reported comparative tests by 19 analysts of the gravimetric and volu- 

 metric methods on cotton-seed meal, South Carolina rock, monosodinm 

 phosphate, and slag. A very close agreement between the results by 

 the two methods was obtained. ^ 



High results were sometimes obtained in the volumetric method when 

 a large excess of molybdic solution was used. Complete precipitation 

 was obtained in the cold when the solution was shaken for 15 minutes 

 or more. 



H. A. Huston suggested that the occasional high results obtained by 

 the volumetric method on slag might be due to the presence of man- 

 ganese. This could be corrected by adding a small quantity of ferrous 

 ammonium sulphate. 



The volumetric method in the following slightly modified form was 

 made provisional. Dissolve the substance according to prescribed 

 methods, except that sulphuric acid must not be used. Make up to a 

 convenient volume and use aliquots corresponding to 0.4 gm. of sub- 

 stance for percentages below 5 or 6, 0.2 gm. for percentages between 

 about G and 20, and 0.1 for percentages above 20. Add 15 gm. ammo- 

 nium nitrate, dilute to 75 to 100 cc, aud heat in a water bath to GO to 

 G5° C. Add 20 to 25 cc. of freshly filtered molybdic solution for per- 

 centages below about G, 30 to 35 cc. for percentages below about 20, 

 and 40 cc. for percentages above about 20. Digest for 15 minutes, filter 

 at once, and wash twice by decanting with water, using 25 to 30 cc. each 

 time, agitating the precipitate thoroughly aud allowing it to settle well. 

 Transfer to filter and wash 5 or 6 times, using enough water to make 

 with decantation washings about 200 cc. Transfer the precipitate to 

 the precipitating vessel, dissolve in an excess of standard alkali, add a 

 few drops of phenolphthalein, and titrate with standard (nitric) acid. 

 Instead of precipitating in a bath at 60 to G5° C, the precipitation may 

 be made at room temperature by shaking for about 30 minutes in some 

 convenient form of shaking apparatus. 



The referee suggested that convenient forms of filters for this work 

 may be made by putting into the glass tube used for holding Gooch 

 crucibles a perforated porcelain disk to which is attached a stout piece 

 of wire. This wire extends through the neck of the tube, and is used 

 to push out the filter and precipitate after filtration. The porcelain 

 Gooch crucible with false bottom and the deep form of Hirsch funnel 

 are also recommended. These three with felts of asbestus and suction 

 give good nitrations. 



Uniform fertilizer legislation. — The committee appointed by the Asso- 

 ciation to confer with a similar comruittee appointed by the Association 



