T E E J O U R N A L O F I N D U S T R I A L A N D ENGILVEERIaVG C H E M I S T R Y
780
Vola 9 , NO. 8
t h e suspicions regarding t h e men's guilt would be k'$ confirmed. The results, however, entirely exonerated t h e men from all blame a n d showed t h e cause t o be due t o t h e poor burning quality of t h e ore itself. At t h a t time I did not have t h e electric furnace, b u t made t h e determinations in one a n d t h e same dish placed on a tripod a n d heated with a small Ni.ker burner, shielded from draughts b y a sheet iron hood. T h e results were as given in Table IV.
c 0 .uc L L- SI 0 x It is well known t h a t as regards available sulfur in pyrites no method has hitherto been presented t h a t does a t all agree with practice. To account for t h e low yield of available sulfur i t is t h e custom in some places at least, t o determine such heavy metals as lead, copper and zinc a n d deduct from t h e total sulfur t h a t equivalent t o sulfates of these metals, b u t even so, there is usually no agreement with practical yields a n d as t h e sulfates of these TABLE IV heavy metals are all decomposable a t a bright red heat, EUSTIS LUMPORE CARRIDAD ORE ACTUALANALYSIS ACTUALANALYSIS t h e temperature of t h e burners, it is evident t h a t such A-Sulfur in ore.. ......... 45 8 7 , A-Sulfur in ore .......... 43.2% B-Sulfur in cinders.. . . . . . 3 OYG B-Sulfur in cinders.. . . . 9 . I 7G a practice is faulty, even if i t occasionally should seem CALCULATION FROM A CALCULATION FROM A t o agree with practical results. 45.8 43 7 The only reliable method of arriving a t t h e available a = - X 2 = 0 8 - . ,40 a = - X 2 = 0.9160 100 100 sulfur content of a pyrites is, as has been shown, t h e f a-x KIP t a - X Kio 15 0.3705 0.02620 15 0.5027 0.01601 determination of t h e rate of change of t h e ore, compared 30 0.1893 0.02282 30 0.3243 0.01435 with some other ore t h a t works normally a n d t h e avail45 0.0446 0.02916 45 0.1945 0.0 1450 able sulfur of which is known. Average Kio.. ........... 0.02606 Average Kio.. . . . . . . . . . . . 0.01495 .'. K, = 2.30259 Kio = 0.06001 .'. K, = 2.30259 Kin = 0.03442 Furthermore, this determination serves as a check 48 upon results already obtained and so helps t o place 9 * 2 43.7 = 0.03442 (100 - z + -x ) : (45.8 - x ) 128.24 51 l'ga-x t h e true explanation upon them instead of subjecting = 100 : 3 a - x = 7.55 g. Sulfur in cinders x = 36.15 Available Sulfur them t o mere suspicions, which, though seemingly a - x = 2.18 g. Sulfur in cinders - burnt off a = 43.70 x = 43.62 g. Sulfur burnt off reasonable, may still be untrue. a = 45.80
- 36.15
100
48 + 1w X 36.15
2.30259log 45.8 = 0,06001
EVERETT,MASSACHL SETTS
2.18
t
= 9.80 per cent sulfur in cinders
t = 51 minutes
Again in November t h a t same year some of this Carridad ore was burned as fines with such unusual low sulfur test in t h e cinders, compared with t h e lump ore, t h a t now t h e suspicion arose as t o t h e accuracy of t h e cinder samples or t h e cinder test. Again, t h e determination of t h e r a t e of change of t h e fines ore exonerated the parties concerned, a n d placed t h e explanation on t h e better burning qualities of t h e fines ore. As i t was not a n y surety t h a t t h e flame could be adjusted t o t h e exact conditions prevailing when t h e test of t h e lump ores was made t h e preceding August, I chose for comparison a sample of Eustis fines ore burned t h e same month as t h e Carridad fines. T h e results are given in Table V. TABLE V
EUSTISFINESORE ACTUALANALYSIS 46.1 % A-Sulfur in ore.. B-Sulfur in cinders.. 2.67, CALCULATION
......... .....
a
CARRIDAD FINES ACTUALANALYSIS A-Sulfur in ore.. ......... 42.2% B-Sulfur in cinders.. . . . . . 2. 1% CALCULATION
4 6 . X 12 = 0.9220 100
t
a - x
15 30 45
0.3962 0,2120 0.0675
a =
KIQ
1
0,0247 0.0214 0.0253
15 30 45
Average Kia., ........... 0.0238 K, = 2.30259 Kio = 0.0548 48 x X ) : (46.1 X) (100
.'.
4 2.2 X 2 100
= 0.8440
a-x
0.3628 0,1941 0.0621
Kio 0.0245 0.0213 0.0252
Average Kio, . . . . . . . . . . . . 0.0236 K, = 2.30259 Kio = 0.0543
.'.
- + 1z4-
= 100 : 2.6 a
THE MERRIMACCHEMICALCOMPANY
= 76.91 per cent cinder
a
-x
= 1.80 g. Sulfur in cinders x = 40.40 g. Available Sulfur burnt off
g. Sulfur burnt off 1.88 Available Sulfut left - xx == 44.22 in cinders
-
a = 42.20
100
48 - 40.4 + 128.24 X
40.4
= 74.72 g. cinders
,%
t = 58 minutes
=
x
100
2.40 per cent sulfur in cinders
A CONVENIENT APPARATUS FOR ELECTROMETRIC TITRATION DEPENDING ON THE CHANGE OF OXIDATION POTENTIAL, AND ITS APPLICATION TO THE DETERMINATION OF SMALL QUANTITIES OF CHROMIUM IN STEEL By G. . I
KELLEY,J. R. ADAMSAND J. A. WILEY Received January 17, 1917
T H E APPARATUS
The apparatus for electrometric titration described b y Hildebrandl and Forbes2 and t h e modified form described by Kelley a n d Conant3 consisted of a number of separate parts, many of which were not well adapted t o purposes t o which they were put. I n t h e present apparatus, which was made for us b y Leeds and S o r t h r u p , t h e parts have been selected t o give t h e greatest efficiency for such work a n d are combined as a unit in a single rugged instrument. The present instrument can be moved about t h e laboratory readily, requiring for its operation only t h e connection of a plug with a n electric light socket. I t is complete in t h a t i t carries a potentiometer system. a motor for t h e operation of t h e stirrer and t h e two burettes for t h e oxidizing a n d reducing solutions. I L L US T R A T I 0 X
B s will be seen in t h e illustration, t h e apparatus consists essentially of a wooden box with a metal upright carrying t h e motor, burettes a n d electrodes. I n t h e box are two dry cells, a n adjustable resistance and a Leeds a n d Northrup reflecting galvanometer of t h e form known as Type 2400. This galvanometer is sufficiently sensitive for t h e purpose and has t h e further advantage of a very short period. On t h e 1 2
8
J . A m . Chem. Soc., 86 (19131, 869. Ibzd., 86 (1913), 1527. I b i d , 88 (1916), 341.
Auy..
IC]!?
r'ff I.; J O [.K.\'.
L I- O F 1 4 1 ) ( S I ' K I .l I
upper siirfzice of thc l i i x is a ground glass plate on which the light from t.he galranometcr is thi-own. This puts it in n position where it may be conveniently observed by the operator during titration. A knob on top of t h e !>ox permits of adjusting the zero point of t h e gal1-rinometer and one on the side controls t h e resistance. A plug and resistance coil. ;ilso on t h e side, make it possi1,Ie t o vary tlic resistance and so increase the range of potentials over which t h e adjustable rcsistance may lie mad:: t o operate. T h e st;iiirlard carries the burettes,
I.VU E N G I N E E K I N G C H E d I I S 1 ' K Y
781
A hard rubber pan, carried on a n adjustable support, serves to center t h e kcr i n which t h e titration is made, and because of stops prevents carrying t h e beaker high enough t o strike t h e elcctrodcs or stirrer. T w o switches are mounted oii tlie box. One controls t h e motor and galvanometer light and tlic otlier throws in t h e potentiometer circuit. All connections, except t o dry cells, are soldered and the insulation i s designed t o make as little iis possible trouble from "leaks." To operate t h e instrument, a beaker containing t h e solotion to be :hnalyzed i s placed on t h e rubber pan, and the support raised and Iockcd in position. T h e swilcli controlling t h e galvanometer light a n d motor is thcn closeti. The other switch closes t h e potentiometer circuit and a slight t u r n of the knob controlling tlie resistance is siifficient t o bring t h e beam of light from t h e galvanometer onto the scale. In titrating a series of sointions at one t i m e lhis !alter adjustment need he made only once. During t h e operation, which is quick, certain and convenient. the analyst watches the beam of light until a permanent change of potential is noted. The apparatus ha factory daily use in this laboratory for for t h e determination of chromium a n steel and lcrro alloys. t o let one or two ilrops pass.
THI: D E I E K X I N T I O S O F S M A L L A X U U X T S OY C I * X O X I U l J I N STEEI,
t h e clecirodcs, a n d t h e motor for driving t h e stirrer. 1x1 adilition, provision has been made for a reservoir
of the eleclrolyte which is used in t h e calomel cell (:I concentrated solution of potassium or sodium nitrate and cnlonicl) t o make conveniently possible without change i n its potential t h e ilisplacement of t h e impure electrolyte which may ha\-e nccumuliited i n the tip of tlie calomel electrodc. This is :accomplished h y opening the stopcock at the top of the electrode enough
X a n y nicthods fur t h e deterniination of chrominm in steel make possible the determination of this element to within 0.01 or 0 . 0 2 per cent of the weight of t h e samlilc. Other more rapid methods show variations amounting t o 0 . 1 0 per cent. I n this paper we give figures showing that determinations may be made which agree within 0.001per cent and which are probably acciiritte to nearly this degree. This has becn made possible b y thc development of the instrument desci-i1,ed ahove. I n a paper b y one of us1 chromium ations 011 a given sample are sliown as varying rai hundredths of a per cent. With this instrument a n d solutions of the same^ strength. these (liflcrences have been reduced t o 0.01 per cent. By using more dilute solutions in the analysis of samples containiiig sm:ill amount,s of chromium, t h e determinations were made with a corresponding degree of accuracy. A stmdart! chromate solution W I ~ S prepared of sucli strength tliat2one liter of solution contained I gram of chromium. Twice crystallizing potassium dichromate of C. 1'. grade. powdering and drying it at 130' for ritl hours gives n product from which solulions niay he ni;idc iiccuriite to I part in joo. If it is desired t o st;ini!arilizc such a solution with permanganate t o a color enii-point, the most convenient procedure is t o st:,ni!ariiize the permanganate b y titration ::gainst sodium ominte. This is next compared with ferrous i d t i l e chromate is finally titrated b y adding . of ferrous suliale and titrating hack with permang:~nate. Care must be taken t o obtain corrertions on blank titrations for all end-points. T i t h -
, T~~~~ jouxnrL, a (1916).719.
782
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
out such corrections, t h e error may amount t o 7 t o I O parts in 1000, t h e figure for chromium appearing too low b y this amount. Even when sodium phosphate is used t h e correction is necessary. It has been t h e custom in this laboratory t o prepare a blank b y reducing t h e chromate solution with SO2 in hot solution, after which i t is boiled gently for I j min. while a stream of CO2 is passed in. The solution is then cooled, diluted t o t h e proper volume and permanganate added gradually t o t h e first permanent change in color. During t h e reduction material reducible by S O 2 other t h a n chromates must be carefully excluded and t h e presence of halogens is t o be avoided also because of t h e action on t h e permanganate. Another method of finding this blank consists in adding a quantity of standard ferrous sulfate solution t o t h e solution of chromic salt, which upon titration will be found t o have required a n amount of permanganate too large b y t h e amount of t h e correction. The end-point obtained has a color which is described as blue by some and as gray b y others. I t appears much earlier t h a n t h e first pink color and i t is a more definite point. This method of obtaining t h e blank is somewhat questionable because t h e color of t h e solution of chromic salts is noticeably different from t h a t which results from t h e reduction of chromates by ferrous sulfate. If all titrations, except t h e titration of sodium oxalate with permanganate, are made on t h e electrometric apparatus, better results are obtained. On this apparatus one may titrate, ( I ) permanganate and ferrous sulfate, ( 2 ) chromate and ferrous sulfate, a n d (3) chromate, using a n excess of ferrous sulfate with respect t o t h e chromate, completing t h e titration with permanganate a n d ferrous sulfate. I n working with different combinations of oxidizing and reducing reagents on this apparatus, we have noted certain characteristic differences a t t h e end-point. Allowance must be made for this if full advantage is t o be taken of t h e accuracy of which t h e instrument is capable. I n titrating a chromate solution t h e addition of ferrous sulfate almost invariably produces what Forbes describes as a n anomalous rise. I n titrating a permanganate solution, this phenomenon does not appear with quite t h e same regularity and is always‘ less marked. I n titrating chromate, t h e change in potential is always abrupt when t h e end-point is reached, b u t with permanganate t h e addition of as many as 0.2 t o 0.4 cc. of ferrous sulf a t e after t h e disappearance of t h e pink color often causes only a gradual change. If now permanganate be added drop by drop t h e return of t h e original potential is delayed until one or two drops cause a marked change. One or two additional drops of permanganate are now sufficient t o produce a pink color. From this point t h e titration of t h e permanganate with ferrous sulfate closely resembles t h e titration of chromates, in t h a t no change occurs until t h e end-point is reached when t h e change is abrupt. I t . has occurred t o US t h a t in adding ferrous sulfate gradually t o a n excess of permanganate, a suspension of manganese dioxide is built up which requires a n appreciable excess of ferrous sulfate for its reduction. On titrating back with permanganate, either t h e condition is overcome,
Vol. 9 , No. 8
or i t is so much less marked as t o have no appreciable effect upon t h e behavior of t h e electrodes. I t is our custom t o a d d ferrous sulfate in excess until there is a marked change of potential. Permanganate is then added gradually until t h e original potential is reached which existed immediately before t h e fall in potential began or until t h e further addition of two or three drops causes no further change. T h e dropwise addition of ferrous sulfate then gives a sharp and definite end-point. I n connection with t h e analyses given in this paper I O O cc. of t h e solution of chromate containing I g. Cr in a liter was diluted t o 1000 cc. A solution of ferrous sulfate of equivalent strength mas similarly diluted. When these solutions were compared their relation was found t o be unchanged. These solutions were of such strength t h a t 0.1 cc. corresponded t o 0.001 per cent of Cr in a I g. sample of steel or t o o . o o o j per cent in a sample weighing 2 g. T h e samples were prepared for titration exactly as described elsewhere.‘ I n t h e table below, we give analyses for chromium on samples of steel issued by t h e Bureau of Standards. The column marked “Certif. Value” contains t h e percentage of chromium given on t h e certificate: i t is not known what accuracy is claimed for these figures, b u t i t is probably not greater t h a n 0.003 or 0.004 per cent. I n t h e case of Sample 33, one analyst reports 0 . 1 1 and another 0.12. ANALYSES OF STANDARD SAMPLES OF STEELFOR CHROMIUM CONTENT SAMPLE PER CENTCHROMIUM SAMPLE PER CENTCHROMIUM B. of S. GramsCertif. Found B. of S. Grams Certif. Found Eo. Taken Value Electr. Titr. No. Taken Value Electr. Titr. 10b ..... 2 0 . 0 0 5 O.OOi(2) 33.. 2 0.11 0.113(5) 2 0.007(2) and 0 . 1 2 3 0.007 (0) 2 0.113(5) 0.007 ( 7 ) 3 0.113(3) 3 16a 2 0.008 0.009(5) 3 0 . 1 13 ( 7 ) 2 0 . 0 0 9(5) 19a 2 0.08 0.076(5) 34.. 2 0.01 0.011(5) 0.076(7) 2 0 . 0 1l ( 5 ) 2 0.076(5) 3 0 . 0 1l ( 3 ) 3 3 0.076(3) 3 0.01 l(5)
..... .....
We believe this t o be t h e most sensitive a n d accurate method known for t h e determination of small amounts of chromium in complex solutions. Of substances ordinarily present in steel, only vanadium interferes. RESEARCH DEPARTMENT THEMIDVALE STEELCOMPANY ’ PHILADELPHIA
THE PHOTOMICROGRAPHY OF PAPER STRUCTURE By MILLARD B. HODGSON Received May 16, 1917
I n t h e s t u d y of t h e ultimate structure of paper, much valuable information can be obtained b y photomicrographs of cross-sections of t h e paper stocks. Some published accounts have appeared from time t o time illustrating t h e matting together of fibers in paper stocks, b u t little has been done in t h e direction of a more intimate s t u d y of t h e subject, a n d t h e possibility of d a t a t o be obtained from photomicrographs of cross-sections of paper has scarcely been touched upon, one reason for t h e lack of work in this last direction probably being t h e difficulty of making cross-sections of paper. 1
LOC.cit.
