28 MASS. EXPERIMENT STATION BULLETIN 379 



5 ml. of potassium permanganate solution treated in exactly the same manner 

 after the addition of 5 ml. of sulfuric acid (1-1). For traces of manganese, discard 

 the color filter and use the white porcelain surface and a more dilute standard. 



sR 



%= X 50 for 2 grams (F) 



Ri 



0.01 25R 



Ri 



125R 



p.p.ni. 



Ri 



s=erams of the standard employed. 

 R=sca!e reading at which the standard was set. 

 Ri=scale reading of the unknown. 

 F=factor for converting the aliquot to percentage or p. p.m. 



The limit of error between parallel solutions should not exceed 0.00010% 

 or 1 p.p.m. 



Determination of Phosphorus 

 (Modified Fiske and Subbarow) 



Reagents 



Standard phosphate solution. — Dry monopotassium phosphate (Soerensen's), 

 transfer 0.8786 gram to a volumetric flask, add water, 25 ml. of 10 N sulfuric 

 acid, and make to 2000 ml. at 25° C. One ml. contains 0.00010 gram of phosphorus. 



Ammonium molybdate solution, 2.50%. — Dissolve 50 grams of ammonium 

 molybdate (NH4)6Mo7024.4H20 in 400 ml. of water and pour slowly with 

 agitation into 1000 ml. of 10 N sulfuric acid and make to 20C0 ml. 



1 Amino-2 naphtholA sulfonic acid solution, 0.10%. — Dissolve 1 gram^ of the 

 purified compound in a mixture of 975 ml. of 15% anhydrous sodium bisulfite 

 and 25 ml. of 20% anhj'drous sodium sulfite, and filter into an amber bottle. 

 In some instances an additional 1 or 2 ml. of sodium sulfite may be necessary to 

 insure complete solution. The solution is unstable but is serviceable for several 

 weeks if protected from heat and light. 



Sodium bisulfite, anhydrous, 15% 150 grams per 1000 ml. 



Unstable, use a fresh solution. 



Sodium sulfite, anhydrous, 20%. 20 grams per 100 ml. 



Sulfuric acid, 10 N, 38.21%. 564 ml. per 2000 ml. 



Purification of 1 amino-2 naphtholA sulfonic acid 



Prepare a solution of 150 grams of anhydrous sodium bisulfite and 5 grams of 

 anhydrous sodium sulfite in 1000 ml. of water and heat to 90° C. Add 15 grams 

 of amino-naphthol-sulfonic acid, shake until dissolved, and filter with suction 

 to remove impurities. Cool the filtrate, add 10 ml. of concentrated hydrochloric 

 acid, and allow to stand over night in a refrigerator to precipitate. Filter through 

 a Buchner funnel, wash thrice with cold water and twice with cold alcohol, dry 

 in a vacuum oven at room temperature, and preserve in an amber glass-stoppered 

 bottle. 



Method 



Transfer an aliquot (10 ml.) of the original ash solution containing about 

 0.0005 gram (0.08-3.00 mg.) of phosphorus into a 100 ml. volumetric flask, dilute 



'The recent product proved more reactive than formerly; hence less is employed. 



