VARIATION OF DUDLEY AND NOYES 169 



merton for the determination of small quantities of phosphoric 

 acid or of phosphorus in the presence of a large excess of iron, 

 has been modified by Dudley and Pease, 26 and by Noyes and 

 Royse. 27 As modified, the method is not intended for fertilizer 

 analysis, but the principle on which it rests may some time, with 

 proper modifications, find application in fertilizer work. The re- 

 duction is accomplished in a jones tube, much simplified, so as 

 to render it suitable for common use. 28 The molybdic acid is re- 

 duced to a form, or series of forms, corresponding to molybdenum 

 sesquioxid, as in the Emmerton method, and subsequently, as in 

 that method, titrated by a set solution of potassium permanganate. 

 The iron or steel filings, containing phosphorus, are brought 

 into solution by means of nitric acid. For this purpose two 

 grams of them are placed in a half liter flask together with 50 

 cubic centimeters of nitric acid of 1.18 specific gravity. The 

 mixture is boiled for one minute, and 10 cubic centimeters of 

 permanganate solution of one and a quarter per cent, added. 

 Boil again until the pink color disappears. Ferrous sulfate solu- 

 tion is next to be carefully added, shaking meanwhile, until the 

 solution clears. Cool to 50 and add eight cubic centimeters of 

 ammonia of 0.90 specific gravity, stopper the flask, and shake 

 until any precipitate which may form is redissolved. Cool or 

 warm, as the case may be, until the solution is as many degrees 

 above or below 60 as the molybdic solution is above or below 

 27. Add 60 cubic centimeters of molybdic solution, stopper, 

 and shake on a machine or by hand for five minutes. After 

 remaining at rest for five minutes pour into a nine centimeter fil- 

 ter of fine texture, and wash with the acid ammonium sulfate 

 solution in quantities of from five to 10 cubic centimeters each 

 time. The filtrate and washings must be perfectly bright. Con- 

 tinue the washings until the filtrate gives no color with hydrogen 

 sulfid. 



Dissolve the yellow precipitate with 12 cubic centimeters 

 of 0.96 ammonia diluted with an equal volume of water, and 



36 Journal of Analytical and Applied Chemistry, 1893, 7 : 108. 

 Journal of the American Chemical Society, 1894, 16 : 224. 



77 Journal of the American Chemical Society, 1895, 17 : 129. 



18 Blair, Analysis of Iron, Second Edition ,1891 : 99. 



