Dec., 1916
T E E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
sulfuric acid and t h e temperature of t h e system. The end-point, however, is definite a n d cannot be overstepped. T h e presence of t h e asbestos is no objection. SUMMARY
A method for t h e analysis of Paris green is proposed by which t h e copper is precipitated as t h e oxalate and t h e oxalic acid combined is titrated with permanganate, t h e arsenic being oxidized in t h e filtrate by iodine after being made alkaline. The procedure is accurate and, with t h e exception of t h e fact t h a t t h e copper oxalate must stand over night, rapid. DBPAPTYBN~ oI GBNBIAL AND ACIICULTURIL Ca~Wlslau
MISSACHUSB~S AGIIFULTUIALCOLLBGH. AMHERST
THE DETERMINATION OF SULFUR IN IRON A N D STEEL By H. B. PULSIPBS Received July 17. 1916
In 1904, Hendrixson announced' t h a t iron dissolves easily in chloric acid, going quantitatively to the ferric condition. At t h a t time t h e author was studying t h e methods for the determination of sulfur in iron and steel a n d a t once recognized t h e possibility of using chloric acid as t h e solvent in t h e analysis. Chloric acid is a highly satisfactory solvent for t h e usual finely granular material used for analysis; t h e action takes place rapidly and with far less gas evolution t h a n when nitric acid is t h e solvent. I n attempting quantitative d a t a on samples of known
XIO. ,*"L*"X
Y R I N T OP C A S T IRON ANCOT
sulfur content t h e work developed largely into a study of t h e uniformity of samples, t h e nitric acid a n d fusion methods, t h e precision of results and t h e work of others. A limited number of analyses by t h e new method indicate t h e difficulties a n d possibilities of its use. From t h e analytical point of view t h e segregation of sulfur in t h e ferrous materials was first mentioned by Eggertz in 1868;' our Bureau of Standards has frequently related its difficulties along the same line, while Bauer and Deissl t a k e particular pains to expound t h e difficulty a n d indicate how t h e analyst shall avoid falling into serious error. This segregation of sulfur is a well known condition to the metallurgist a n d metallographer; with sulfur 1 J . A m . Chcm.,Sor., 26 (1904). 747. SChmr. N m s . 18 (1868). I S .
,"Sampling and Chemical Anelysis of Iron and Steel," translated by
Hall nod Willinmr, 1916.
11rg
prints a n d through t h e microscope the actual condition is f a r more truthfully revealed t h a n from the reports of t h e analyst who may rely on one single result or unwittingly fail to indicate t h e diversity of his check determinations. The statistical method of studying t h e distribution of results would be highly illuminating hut is hardly practical because of t h e material, time a n d labor required. I n no case on the samples here studied were less t h a n duplicate results obtained; often 3 and in several cases 6 or 7 determinations were run for t h e sake of establishing a mean value of t h e sulfur content. P R E P A R A T I O N OF S A N P L E
W e suppose t h a t sulfur occurs in our materials a s sulfide of iron, sulfide of manganese, or indeed as a double sulfide of t h e two. These sulfides are probably quite insoluble in t h e more common a- and @-modifications of ferrite for we have no difficulty in discovering t h e particles with the microscope when only a few hundredths of one per cent of sulfur are present in t h e metal. This discrete occurrence of sulfur in t h e metal, and in particular its segregation in t h a t portion of a n ingot which solidifies last is perfectly well known t o metallurgists and metallographers. The bearing of this on t h e results obtained by t h e analyst is highly significant. Even more imperative is its dictum regarding t h e preparation of t h e sample. I n a j-g. sample of metal i t requires about O.OOOOS
RG.
II-SuLllua
P N N T 0 s STeB,. S H * I T I N C
g. of sulfur or 0.00014 g. FeS or MnS t o influence thc analysis by 0.001 per cent. This is represented by a cube of t h e substance 0.3 mm. on a side; such a particle will barely pass a So-mesh screen. For some degree of safety, then, t h e material should pass an 80-mesh screen a n d be thoroughly mixed; this material would be uniform t o about 0.001 per cent, in j-g. lots. The actual loss of sulfur by such treatment awaits investigation. Variations due t o analytical conditions might still cause deviations. Figs. I t o IV visualize this common characteristic of materials, Fig. I is a full-size sulfur print made hy photographic paper on a small ingot of cast iron. I t shows t h e spots of sulfide throughout the entire section and, in particular, t h e layer a t t h e top which is extremely high in sulfur. The accurate sampling of such a n ingot is obviously quite a task. Analyses of crushed millings gave the following results:
T H E J O U R N A L O F I N D U S T R I A L A N D EiVGINEERING C H E M I S T R Y
IiI6
TABLEI-PERCENTAGESOF SULFUR Original Crushed Millings
AFTERGRINDING
20 to 100 mesh
Through 100 mesh
0.201
Some of the material which persisted coarsely granular even after t h e twenty passes through the disc grinder was probably high in sulfur although small in amount. Fig. I 1 is another sulfur print of a section of shafting showing high sulfur spots. Figs. 111 a n d I V are photomicrographs of this material a t 2 0 0 diameters, suitably etched. The two prints were of spots a bare halfinch apart on the metal surface. Fig. 111 shows fine, practically sulfur-free metal; Fig. ITr shows typical sulfides. Each cube t h e size of t h e dark spot would p u t 0.001 per cent of sulfur in a 5-8. sample. Remembering t h a t t h e entire area of Fig. I V represents a n actual surface of only 0.16 sq. mm. and is just a trifle too large t o pass a jo-mesh screen we are naturally not surprised t h a t t h e results of analyses on coarse turnings varied from 0.06 t o 0.09 per cent sulfur. For real precision t h e analyst can best determine the limits of the sulfur range on the weight of sample and fineness selected. The average result is, of course, the best value available. The fallacy of any selection which sorts out one size of particle is plain; nothing could be more untechnical t h a n t o pound t h e material a n d screen out a portion for analysis. T h e great objective is how t o reduce a lot t o t h e desired size; a t the present moment there is no light on t h e difficult 1-. M E T H O D S O F ANALYSIS
A perusal of t h e accompanying bibliography in t h e original allows one t o classify t h e methods for sulfur determination according t o t h e following scheme: I-Direct combustion in oxygen. 11-Volatilization as SCl2 in chlorine at red heat. 111-Volatilization with Hs and COZat red heat as Has. IV-Fusion of powdered sample with oxidizing alkaline salts; sintering of powder with MgO and NaOH. \‘--Oxidizing both iron and sulfur with acid solution (or halogen) ; precipitation of sulfur direct or after various manipulations. A-Bromine. B-Concentrated HN03. C-KC103 and HCl. D-Aqua regia. E-Bromine and HC1. F-HNOa and KClOs and KBr. G-Chloric acid. VI-Nitric acid solution and fusion of the evaporated mass. VII-Solution of iron leaving sulfur and sulfides ready t o filter off and oxidize by acids or fusion. A-Ferric chloride solution. B-Copper-alkali(Na, K, or NHd)-chloride solution. VITI-Sulfur evolved as HzSwith HzSO4, or HCl, or both. A-HzS oxidized to H2SO4 direct or after precipitation of a metal, weighing as BaSOa. Oxidation by: I-Bromine. a-Chlorine. 3-Permanganate.
V O ~8, . NO. 1 2
4--Hydrogen peroxide. 5-Sodium peroxide. 6-Lead peroxide. 7-Hydrogen flame and permanganate. E-HzS determined volumetrically. r-Iodine titer directly. a-Iodine in excess and back with thiosulfate. 3-Iodine liberated by KkIn04, back with thiosulfate. 4-Direct titer with KhInO4. (Absorbents for these 4 are NaOH, KOH, salts of P b , cd and Z ~ Z ) 5-FeC13 is reduced to FeC12 and run back with KnCrzOr 6-ZnS reduces Fe”’ to Fe” and back with _KMnOd _ _ .._=~
7-Absorb in NaOH and titrate with Pb(N0a)z. 8-Absorb in standard arsenite and back with iodine. 9-4Absorb in AgN03to AgS and KSCN titer. C-HS determined gravimetrically, weigh as CuO, AgS, Ag, As203 or BaSO4. D-Colorimetric determination of HgS. I-TJse a Pb salt. 2-Cd salt gives CdS. 3-Absorb in As208 solution. 4-Formation of methylene blue. 5-Gives color t o metal foil. E-H*S precipitates PbS, to be read in graduated tube after whirling. Concerning these methods of analysis a few explanatory remarks will indicate their relative importance and certain conditions of use. Method I has been abandoned, after trial, except for particular ferro-alloys. Method I1 is justly dismissed without comment, Method I11 has some figures t o substantiate i t , b u t has too many inherent difficulties. Method I V has been supported b y considerable evidence of accuracy and b y several workers. The material is best very finely powdered, a serious objection. Manipulation may also be objected to. Extremely slight practical use apparently attaches t o the method. Method V is widely used in one or another form, especially for more precise work. S i t r i c acid used as solvent must be replaced b y hydrochloric and t h e silica is best rendered insoluble b y baking. The ferric chloride may be separated by ether or t h e iron may be precipitated with ammonia and either t h e sulfuric acid washed out of the hydroxide or the hydroxide dissolved out of the already precipitated barium sulfate. Ferric iron may be reduced t o ferrous b y a variety of reagents or the same prevented from entering the barium sulfate precipitate b y using organic substances t o form complex ions unaffected b y the precipitation. Residues remaining after the acid treatment of t h e original sample may get special attention and t h e sulfur recovered added t o t h e main portion. This method has been abundantly disparaged and can, of course, be proven inadequate b y uncritical operators. On t h e other hand, t h e method has been substantiated b y abundance of t h e best work and nothing less t h a n fresh evidence can shake it. The precipitation of t h e barium sulfate in t h e ferric chloride solution has been checked as accurate b y workers of
Dec., 19 16
.~
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
..
1117
-
- ~ - r 7:v.c .>-=--~
,
. .%
I
Fro. 111 X ~ ~ & S B C T I Oos N STBEL Sw~sima
Fro. I V
X 2 0 0 4 B c T 1 0 ~HAL# INCHDISTANT
FINS.PIIACTICU.LY SULPUX-FRB METAL B
A table covering this point is offered in this paper a s bearing directly and unequivocally on this point. Method VI is generally considered a n excellent control method. Method VI1 is both old and new and theoretically excellent; the slowness of solution is always against it. Method VI11 has received by far t h e most attention from earliest t o latest times, as t h e history of sulfur determination ranges. Samples may be annealed before dissolving, without or with admixed reagents. The evolution may be effected by acid alone or in t h e presence of hydrogen or carbon dioxide, or both. The gases may be passed through a red hot tube. The residue may be oxidized wet or by fusion or treated with hydrogen and hydrochloric acid a t a red heat, any recovery being added to t h e main portion. The cumulative evidence is t h a t quick evolution with concentrated hydrochloric acid gives a close approximation if not t h e exact sulfur content. Only in unusual cases will sulfur persist in t h e residue. The author has experimented considerably with this method b u t delays results for a later communication. A complete review a n d digest of t h e whole subject is needed but requires far more space t h a n t h e importance of t h e subject would warrant. As other workers have established the accuracy of t h e nitric acid method by attempting t o measure or recover barium sulfate from the filtrate, a procedure always liable t o renewed error through impurities a n d the environment, the author ran a series of 28 lots simply t o establish t h e actual recovery on a measured amount of sodium sulfate. Every condisix nations.
PROM
FIG. 111
S T B ~ROTTEN L W ~ T HSYL~IDBS
tion closely approached t h a t of a n actual analysis. The ferric chloride solution was made by dissolving 560 g. of t h e pure solid salt in z liters of water, filtering and using 50 cc. in each case. The sodium sulfate solution was made by dissolving 1.120 g. of t h e pure fused salt in I liter of water: I O cc. were taken in each instance with a pipette delivering 9.996 cc., temperature corrected. All determinations were made a t t h e same time with a TABLE! II-DBTBRUINATIONS TO SROW~ n l lI N ~ U R N C OP S HYDROEHLOR~E ACID ON TXB SOLUB~L~TY 01 B ~ a i u rSVLIITBIN F ~ a a i cC R L O R ~ D B SOLUTlON
NO. 1.
4 5
FeClr Grams
..............
NaOO.
None
...............
...............
None 14
Gram*
CC.
0.02 0.02 0.02 0.02 I .oo
3.50
4.w 4.50
5 . 0
..........
0.00l1I
0.0004
1.00
0.20 0.40 0.60 0.80 1.00 1.20 I .40 1.60 1.80 2.00 2.20 2.50 2.80 3 . IO
25 ............... 26..... 27 28
Weight BaSO. Gram No ppt. No ppt. 0.0205 0.0204
HCI (1.19)
I4
I4
t I7
.........
5.50 ' 6.w 6.50 7.w
...
...
Fe pptd.
Fe ppfd.
Fe pptd. Fe pptd.
.
0.0221 (red) 0.0206 (red) 0,0207 (pink) 0.0204 (pray) 0.0204 0.0210 0.0200 0.0205 0.0209 0.0203 0.0204 0.0210 0.0207 0.0209 n.0203 0.0207 0.0208 o.0207 0.0206 0.0002
volume of 1 2 0 cc.; precipitations were made hot; solutions stood a t t h e boiling point for a n hour, then over night before filtering. Precipitates were washed 3 times with hot dilute hydrochloric acid ( I O cc.
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T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
Vol. 8, No.
12
1.19 acid in 7 j o cc. water) a n d I O times with hot tion took place a t once. Enough hydrofluoric acid water. was add.ed t o dissolve t h e separated silica and imT h e barium sulfate equivalent of 0 . 0 1 2 2 g. Sa2S04 mediately t h e solution was digested with I O cc. conc. is 0 . 0 2 0 0 g. BaS04. hydrochloric for z or 3 min. over a flame. The mixT h e conclusion seems inevitable t h a t moderate ture was then filtered through a 7 cm. paper with sucamounts of hydrochloric acid do not appreciably in- tion, and I O cc. conc. hydrochloric acid were added to crease the solubility oE t h e barium sulfate in the ferric t h e filtrate which was evaporated t o small bulk. chloride solution. The residue on the paper was placed on a little The details of t h e nitric acid and Bamber's method sodium peroxide and sodium carbonate mixture in are well known and do not need repetition here. Ordi- a nickel or silver crucible, some of t h e mixture placed nary directions for t h e nitric acid method s a y t o add above for a cover, and with the crucible cover held a little sodium salt t o hold t h e SOa. What direct down with the tongs the crucible heated in a bare evidence this is based upon, the author has not been flame. After t h e flash the melt may be swirled t o able t o find; the measurements available indicate complete ftlsion and then poured on metal. If t h e t h a t ferric sulfate begins t o decompose somewhat chloric acid is barium-free t h e melt may be dissolved above 300' C . ; z o o o C. was t h e temperature of t h e in dilute hydrochloric acid and added t o t h e main porlaboratory hot plate. N o sodium salt was added in tion. If t h e chloric acid contained barium t h e melt a n y of t h e analyses. is t o be dissolved in water, filtered, acidified, and then Bamber's method was carried out with the aid of added t o the main portion. a vacuum desiccator, an electric muffle and an elecThe united solutions should now contain about t h e tric hot plate for evaporating t h e water extractions of right amount of free a.cid and if clear may be brought t h e fusions. During evaporation in t h e desiccator t o I O O cc. volume for precipitation of t h e sulfur as t h e temperature was about 9j" C., t h e gauge at from barium sulfate. If the solutions ha.ve separated 1 0 t o i s in. and a current of air was let in through silica they must be filtered before making up t o standcotton. In the electric muffle the mass dried in a ard volume. T o the hot solution IO cc. of I O per cent platinum dish was exposed t o a temperature of 900" barium chloride solution are added, the beaker is placed C. until red hot throughout, which required from I t o t o keep just, below boiling for a n hour, then set aside 3 min. t o cool and filtered the next morning. The barjum None of the reagents used contained measurable sulfate is filtered! ignited and weighed as usual. amounts of sulfur in t h e amount used for analysis. Sodium fluosilicate may separate on mixing the two Blanks run on Bamber's method indicated t h a t solutions or later. This is one of the most insoluble check analyses carried through in every detail ex- sodium salts and if i t appears must be washed out actly like a complete determination would average with hot water. On this account as little hydro0.006 per cent sulfur. I t is t o be noted t h a t such a fluoric acid and sodium salts as possible should be used. blank does not determine any impurity in t h e re- The crystals are large and transparent and easily noted agents but rather what has strayed in b y accident. if present. The c o r n p a r a t i d y long evaporations and numerous Sulfur present in the chloric acid must be corrected handlings make t h e process highly liable t o positive for on the final result. error: as already noted, dust bearing 0 . 0 0 0 0 j g. sulfur PRECISIOK O F RESCLTS mould increase results b y 0.001per cent. The laboraA little familiarity with this t y p e of analytical work tory v a s far from free of dust and fume, as a beam of light will demonstrate in even a reasonab!y clean place, brings out clearly those sources of error which make and during the three days of an analysis it is no wonder u p the inequality of the results as recorded in Table that, most of the samples ran high by this amount, 'lL. TABLE IIi---AAVERAOE RESULTSBY TLIE THREEM E T H O D S I t is more surprising t h a t some of them checked the i\-IPRIC A C I D BAMBER'S CIILORICACID Ax-. c j , s Probable Lots % Av. Probable Error I,cts 7Av. c S Probable nitric acid method a!most exactly. As this throws :;?;;:I a n element of uncertainty on both the analyses and the 1I ~ ~ 4 0.008 ~ . 0.001 3 0 . 0 1 6 0.002 2 0.014 0.007 blanks t h e only conclusion is t h a t for strictly reliable ,4. 0 , 0 1 8 0'001 2 00.015 ' 0 1 4 0'003 0.003 tile process must be carried in a ab4 I r o n . , . 5 0.013 0.001 3 0,'Oil 0 : h d l 2 0.023 0.001 2 0 . 0 1 6 0.001 5 0,020 0.001 5 Steel. , . 3 0.018 0.002 2 0.038 0.002 6 0.034 0 , 0 0 2 solutely dust. and juIne.free and \
