THE EXACT DETERnINATION OF PHOSPHORUS BY THE MOLYBDATE METHOD IN IRON, STEEL, AND ORES, WHICH CONTAIN ARSENIC. ’ BY J A M E S 0. HANDY, Chemist of The Pittsburgh Testing Laboratory. L’t’d. C L A S S I F I C A T I O N O F E X I S T I N G METHODS F O R PHOSPHORUS.
T h e acetate method of Blair and others. T h e molybdate methods. ( a ) Methods in which the phosphoniolybdate is weighed (methods of E. F. Wood and others). ( b ) Methods in which the amount of yellow precipitate is estimated volumetrically. (a‘) By permanganate (methods of Emmerton, Drown, Jones, and others). (b’) By alkali (methods of Manby, Handy, and others). 3. T h e coinbination methods. ( a ) T h e acetate and molybdate methods. (b) T h e molybdate and magnesia methods. I n the “ acetate” methods the phosphorus is precipitated as phosphate, after separating by hydrogen sulphide, any arsenic which is present. T h e methods are long and the manipulation difficult. In the “ molybdate ” methods, the phosphorus is precipitated as ammonium phosphomolybdate and weighed or titrated. Arsenic, which is believed to be of rare occurrence, is disregarded. It is, however, a fact, that, when arsenic is present in a solution from which phosphorus is precipitated as phosphomolybdate, a .portion of the arsenic accompanies and contaminates the phosphorus precipitate. T h e “ molybdate ” methods are in general, very short and their inanipulation simple ; they are widely used. With the drawback of arsenic interference removed, the molybdate method takes front rank for simplicity, brevity and accuracy. I.
2.
1 Read
at the Baltimore meeting. December 28, 1893.
J O.Haudy
0050 0 oio
0
750
I.*;0 0.103
0.012
i ojw
0.012
1.000
0.036 0.036
0.100
0.150
0.a3 0 IO0 o 0'33 0.1jo 0.29;
0.500
0.292
0.500
0.~96
0.500 0,500
waporat'n 1 [neutraJizIn weighing ~
Ferro-niang'se lroii ore
Jfang'seore
0.~12
I
1
j, ,
"
o ~ i j ~
I
,,
..
: 0.264 0.I
__
0.0;3 n.oj2
PROVISG THAT XKSESIC IIOES so'c PRECII'IT:lTE W H E S LITTLE O R N O P H O S P H O R U S IS I'KESEST.
EXPERIMENTS
E=cperiiiiE?zfS.--T\Vo grams of magnetic iron ore, ( a very pure concentrate), showed o.oozper cent. phosphorus. X duplicate containing 0.joo per cent. of arsenic, i i i the fully oxidized form, showed also exactly 0 . 0 0 2 per cent. of phosphorus. T h e filtrate, which contained arsenic, was heated for a short time to 60'--70' C. before molybdic acid or arseiioniolybdate began to separate. T h e saiiie result \vas repeatedly obtained with arsenical filtrates froiu pliosp1ioiiiolyi)tlate precipitates. X solution of arsenic acid in nitric acid, properly prepared a s for phosphorus deteriiiiriation girres 110 precipitate at 85' C. ~ v i t h niolyhdate solution unless the heating is coiitiiiued. T h e experiments tlescrihed prove very clearly that the precipitation of arsenic with phosphoniolybdate is a mechanical one ; that the arsenic is only dragged clown. IVith little or no phosphorus, 110 arseiiic precipitates. T h e case is parallel to the contamination of t!ie first ferric
EXACT D E T E R M I N A T I O N O F P H O S P H O R U S , E T C .
233
hydroxide precipitate, with lime, or of the first oxalate of lime precipitate, with magnesia. In these cases, solution and re-precipitation of the contaminated precipitates, effects their purification. Experiments (Table 11) prove that the same treatment, properly applied, is equally efficient in purifying arsenical phosphoniolybdate. T h e exact method of procedure follows : TABLE11. ELIMINATION OF ARSENIC FROM PHOSPHOMOLYBDATE. 1
"8 f
1 ofTemperature precipitation.
s
Steel
o.jw 0.500
0.96 0.96 0.96 0.96 o.oqb
J. O.,Handy
0.500 1.000
none
0.96 0.96 0.96 0.~96
0.500 0.500 o.jw
0.038
0.038 0.038
..
Pig iron ,/
Ferro-lnaiig's rig iron Iron ore Manaanese iVnTF -A
1
1
0.jw
0.96
0.M
none
0.95
0.001 0.001 0.001
0.95
0.OOI
0.94 0.97 0.C94 0.036
0.002 0.001 0.002 0.002 0.001 0.001
0.97 0.97
0.037
0.500
0,039 0,037 0.081 0.081
0.001
i o ,
0.282
0.500
0.281
0.001
0.266'
o.500
0.289
0.003 8 0.002 0.001
0.038 o.082 0.082
0.085
0.001 0.001
-0.200
l i t t l e lost
THE X E T H O D O F R E D I S S O L V I N G T H E P H O S P H O M O L Y B D A T E A N D F R E E I N G IT F R O M A R S E N I C .
Having separated the phosphorus as phosphomolybdate by any good method and washed it well with one per cent. nitric acid, place a twelve ounce Erlenmeyer flask under the funnel. Dissolve the yellow precipitate by ammonium hydroxide wash ( I : 6 ) , using about fifteen cc. in all, and wash it into the flask. Dilute the solution to about seventy-five cc. and heat to 75' C. and add a mixture of ten cc. HNO, (1.42) and twenty-five cc. of niolybdate solution (E. F. Wood's formula), shake well, filter and wash
2 34
DOOLITTLE A N D E A V E N S O N
[ a ) with one per cent. nitric acitl, dry ant1 weigh, or ( h ) with one per cent. nitric acid and ,I,., per cent. potassium nitrate, tlissolve and titrate (Handy's niethod).
T h e greater part of the analytical work of this paper has been done by illy assistant Mr. Geo. 0 . Loeffler. METHODS l~S*~ll For SfeeC a d Pig-iron.-The inethod used in a11 analyses of steel atid pig-iron, was the oiie published by the author in 1892 ( Tmns. Engimcr's Society of W e s f e m Pe.nnsyhania March, 1851.2, nriti]. A n a l . .4$$. Chmz., April, 1892). Foie Fei-roi,iai~~anc,se.-Two grams, dissolved iii nitric acid, ( I . 4 2 ) , and the solution evaporated to dryness. T h e residue, having been redissolved in hydrochloric acid, ( I . 2 0 ) the solution was diluted arid filtered. Tlie filtrate was treated with ainriioniuiii hydroxide till aiiimoniacal, then acidified with nitric acid, heated to 85' C . and precipitated with fift17 cc. of molybdate solution. Foi- /?-on and Manga7rcse Oim.-T\vo granis dissolved in aqua regia (five per cent. H Y 0 , ( 1 . 4 2 ) miti ninety-fire per ceiit. HCl ( I . 2 o ) , and the solution evaporated to dryness. Subsequent procedure was as described above for ferroniaiiganese after the evaporation. Phospliorus, in ' ' insoluble residues \vas separated and tleteriiiiiietl. .-lrse?zic n ~ i s added as d r y Xs,O., to the samples Ivhen \wiglied oiit. Tlie reagents used i n the analysis oxidized it to arseiiic ositlr. "
NOTES AND QUERIES ON DR. DUDLEY'S METHOD O F DETERMINING PHOSPHORUS IN STEEL. 0 . 5. ~ O O I . I T T 1 . 1 : . C H K l I I S T , A S D .lLl3.\X 1 < . \ \ - E S S O S . . 1 S S l S T A S T c l i K 3 f l S T ~ ' l i l : A I > ~ L l ' H l . XA S 0 R E A U I S Gl < . X l l , X O ~ I >C O > l I ' X S Y . X..,.Cl\i.!I 1.c """'\
T
1 ' ) .
Ib?l,
H E object of the work outlined i i i this paper was to ascertain
the accuracy of the iiiethod proposed by Dr. Dudley for the volumetric analJ-sis of phosphorus in steel, described in /. Auz. C/zc*m. Soc.! Sept., z893, p . 519, and to tlctcrniirie if a separation of phosphorus could he made in the presence of arsenic with a sufficient degree of accuracy for coiniriercial purposes
