Xug
,
1916
T H E JOCR.VAL O F I . V D 1 7 S T R I d L A N D E Y G I S E E R I N G CH E M I S T R Y
drying apparatus which has changed t h e formula used by a number of the larger manufacturers. T h e continuous drying apparatus allowed the manufacturer t o TSABLE 11-TABULATION O F RESULTS (PERCENTAGES) Sample No. 1 2 3 4 5 6
7
Fatty Mois- Anhy- NazO ture dride a s Soap 3 7 . 8 2 18.39 2 . 6 3 22.06 19.44 3 . 5 8 23.75 21.63 2 . 7 1 20.86 18.93 2 . 6 5 18.52 20.34 2 . 6 8 43.38 16.74 2 . 2 3 30.40 21.46 2 . 8 6
UnsaTotal ponified Soap h'a2C03 NazSLOe NaCl M a t t e r 0.45 21.02 39.37 0.55 0.69 23.02 53.53 0.99 0.75 0 . 2 4 24.34 50.35 0.72 0.35 0.85 2 1 . 5 8 55.38 0.90 0.86 0.45 23.02 56.45 0.36 1.32 0.74 18.97 3 6 . 3 0 0.72 0.34 0.87 24.32 4 0 . 0 0 0.99 0 72 0 . 7 9
Total Per cent 99.90 100.59 100.36 100.03 100.41 100.58 97.22
increase the water content of t h e product a n d to lessen the amount of soap. Previously this addition,of water resulted in an inferior caked powder. The determinations made show t h a t the soap powders consist essentially of sodium carbonate and soap. This should be the case from t h e method of manufacture employed, i. e., t h e soap stock, caustic alkali and soda are incorporated and the product prepared similar t o t h a t of soap. After hardening it is ground into the powder form in which it appears on the market. UNIVERSITY OF WISCONSI.I-. MADISON
THE DETERMINATION OF CHROMIUM AND VANADIUM IN STEEL BY ELECTROMETRIC TITRATION By GEORGELESLIE KELLEYA N D JAMES BRYANTC O N A N T Received January 12, 1916
The method t o be described includes t h e solution of the steel in acid, t h e oxidation of t h e elements in question under suitable conditions, and t h e titration of t h e solution with ferrous sulfate using the electrometric method of determining the end-point. This method of titrating chromates has been described recently by Hildebrand' a n d by Forbes and Bartlett,2 and has been applied b y t h e authors t o t h e determination of ~ a n a d i u m . ~T h e apparatus is in all respects identical with t h a t described elsewhere for the determination of vanadium and therefore will not be dealt with here. DETERMINATION
OB C H R O M I U M Ii% S T E E I
I t was hoped t h a t b y t h e application of t h e electrometric method t o t h e determination of chromium, a n accurate and rapid method could be devised for the determination of this element. T o this end t h e oxidation of chromium salts t o chromates was undertaken after t h e methods suggested b y W a l t e r ~ Rich6 ,~ a n d Tusker.6 These methods were selected because of their simplicity and because they involve no filtering. I n these methods ammonium persulfate is used to oxidize chromium and manganese t o chromate and permanganate, sometimes with t h e addition of silver nitrate. Hydrochloric acid, added in small amounts t o the hot solution, serves t o reduce t h e permanganic acid, b u t is without action on t h e chromates. On trying the different modifications of this method which have been published, extremely variable and unsatisfactory results were obtained. This experience 1 2
3
L 5 6
J . Am. Chem. SOC.,35 (1913), 869 I b i d . , 35 (1913), 1527. I b i d . , 38 (19161, 341. M e f . Chem. Eng., 12 (1914). 310. Ibid., 13 (1915), 239. C h e m . - Z f g . ,39 (1915), 122.
719
led us t o undertake a more careful study of t h e conditions necessary t o make t h e method work with certainty. I t seemed possible t o us t h a t t h e following 'errors might interfere with the successful working of the method: ( a ) Incomplete decomposition of ammonium persulfate, ( b ) incomplete oxidation of chromium, (c) reduction of part of t h e chromate b y hydrochloric acid during t h e breaking u p of permanganic acid, and ( d ) incomplete reduction b y the hydrochloric acid of manganese in the higher states of oxidation. ( a ) a n d ( d ) would t e n d t o make the results too high, while ( b ) and (c) would have the opposite effect; thus it might be possible for some of t h e errors t o exist undetected because of counterbalancing. We therefore planned t o test each point separately. D E C 0 RIP 0 S I T 1 0 N 0 F A M 410 K I U M P E R S U L F AT E
Eight solutions of 300 cc. volume, each containing g. of chromium as chromate and 65 cc. of sulfuric acid (sp. gr. I . zo), were heated t o boiling and j g. of ammonium persulfate added. The solutions were then boiled in groups of two for j, I O , I j and 3 0 min., after which they were cooled and titrated with ferrous sulfate, using t h e electrometric end-point. The potassium dichromate solution had been standardized against ferrous sulfate electrometrically and this in t u r n had been compared with standardized potassium permanganate solution. From t h e experiments shown in Table I , it i s evident t h a t j min'. boiling of such a solution does not 0.0102
TABLE I-THE
DECOMPOSITION O F AMXONIUM PERSULFATS 0.0102 G . Chromium Present in Each Case 10 15 30 Time of Boiling (min.), , , , , , , , . . , , . , , 5 0 , 0 1 5 9 0,0101 0.0095 0.0096 Chromium Found (g.).. , . . . . . . . . . . . . 0 . 0 1 9 6 0.0117 0 . 0 0 9 4 0.0082
{
completely remove t h e ammonium persulfate and t h e oxidizing agents into which it decomposes. Even I O min. is insufficient in some instances. Boiling for a much longer time has t h e apparent effect of reducing some of t h e chromate, for t h e values are uniformly lower t h a n the expected values. I t is not improbable t h a t this reduction goes on from t h e first, b u t its effect upon t h e titration is masked b y t h e fact t h a t other oxidizing agents have not been removed. This may be explained as due t o t h e breaking down of t h e ammonium persulfate in acid solution t o give Caro's acid and hydrogen peroxide, both of which reduce chromium. We believe t h a t any method depending upon ammonium persulfate alone for its oxidizing action can give correct results only b y a balancing of errors. This opinion is supported by other experiments in which t h e sulfuric acid mentioned above was changed t o higher and lower concentrations, a n d in which it was partly and completely replaced b y nitric acid. DECOMPOSITION
OF
AMDIONIURI
PRESENCE
PERSULFATE
IK
THE
OF SILVER KITRATE
h4arshal11 suggested t h e use of ammonium persulfate and silver nitrate in dilute nitric acid as a n oxidizing agent for manganese. Experiments parallel 1
Chem. S e w s , 83, 16.
T H E JOCRNAL OF INDC*STRIAL A S D E S G I S E E R I S G CHEMISTRY
20
t o those shown in Table I were tried, using the same volume of solution and t h e same amounts of ammonium persulfate and potassium dichromate, b u t adding in every case I O cc. of a solution of silver nitrate which contained I . 3 g. of -4gSOa in a liter. The sulfuric acid (sp. gr. I .2 0 ) was replaced by nitric acid !sp. gr. I . 13) as indicated in Table 11. TABLE11-DECOMPOSITION OF AMMOKIUM PERSULFATE
I N PRESEKCE SILVER NITRATE Initial Volume. 300 cc. 0.0102 G. Chromium Present in Each Case Acid Used.. . . . . , . . . , , , , , , , , . $0 c c "01 GO cc. HlSOa 60 cc. "08 Time of Boiling.. . , . , , , , , , . , . 3 min. 30 min. 30 min. 0.0103 0.0101 Chromium Found ( G . ) . . . . . . . 0.0103 0.0101 0.0101
OF
1
T h e variations found in t h e experiments recorded in Table I 1 are within t h e experimental error of t h e method and show t h a t in t h e presence of silver nitrate the course of t h e decomposition of ammonium persulfate is very different from t h a t which i t follows when this salt is absent. This follows from the fact t h a t no oxidizing materials, except t h e chromium, were present after 5 min.' boiling, and 30 min.' boiling did not result in t h e reduction of a n y chromate. The presence of nitric acid does not appear t o be necessary, b u t since in t h e analysis of steel t h e iron in t h e sulfuric acid solution of t h e sample is most conveniently oxidized with nitric acid, t h e effect of nitric acid was determined. T H E R E D U C T I O N O F O X I D I Z E D M A K G A N E S E JTITH HYDROC H L O R I C ACID
Solutions containing 0 . 0 0 j g. of manganese as manganous sulfate, a n amount corresponding t o 0 . j per cent of manganese in a I-g. sample of steel, were treated with nitric or sulfuric acid, as specified in Table 111, and made up t o a volume of 300 cc. The TABLE111-EFFECT
OF SM.4LL
AXOUNT
OF
COLD HYDROCHLORIC ACID ON
TITRATION OF MANGANESE
O - xdizinr
"01 (So. Gr. 1.13) 3 drops GO 'cc'. 60 cc.
HzS04 (Sp. Gr. 1.20) 300 cc. 60cc.
..
CHROMIUM Taken Found 0.0010 0.0010 0.0069 0.0070 0.0081 0.0081 0.0081 0.0081
Materials Found in Terms of Chromium 0.0000 0.0001 0,0000 0,0000
solutions were heated t o boiling and I O cc. of t h e silver nitrate solution added, followed b y j g. of ammonium persulfate. After boiling 7 min., I cc. of dilute hydrochloric acid (I acid : z water) was added, and boiling continued for j min. I n all cases t h e solutions had a red color after t h e addition of ammonium persulfate; and they became colorless after the addition of hydrochloric acid. T o detect oxidizing substances left in the solution. after cooling, a measured amount of potassium dichromate was added and the solution titrated with ferrous sulfate as usual. Under t h e conditions of t h e experiments shown in Table 111, t h e oxidation and reduction of manganese were entirely satisfactory for t h e purposes of the method, inasmuch as no unreduced manganese compounds were left in t h e solution after t h e treatment with hvdrochloric acid. Subsequent hToTk on t h e method as finally established for t h e analysis of steel showed t h a t t h e oxidation of manganese b y ammonium persulfate was by no means as simple 'as might be supposed. On the addition of the oxidizing agent t o the hot solution, the
1-01. 8, No. 8
coiors resulting after a few minutes' boiling would vary from a light pink, a deep red, a murky brown and finally an actual precipitate of manganese dioxide, depending on t h e amount of manganese present. On t h e addition of hydrochloric acid t o such solutions, thase having a pink or red color would grow yellow (in the presence of chromium) or colorless, in the course of z min. T h e dark brown solutions would lose their color and turbidity only after boiling j t o 7 min., while solutions containing precipitated manganese dioxide failed t o clear up, except o n prolonged boiling with a larger aniount. of hydrochloric acid. I n spite of the fact t h a t large amounts of manganese cause the solution t o become murky and even t o precipit a t e manganese dioxide, it has been found possible t o determine Cr in a I-g. sample of steel when t h e amount of manganese corresponded t o 3 per cent. This is possible for two reasons: ( a ) When such a solution is obtained in t h e presence of the other products of solution of steel there is less tendency for t h e manganese t o precipitate as oxide; and ( b ) if t h e acid concentration is kept reasonably high ( 6 0 cc. of sulfuric acid of sp. gr. I . 20 t o 300 cc. of solution) a very high percentage of manganese is necessary t o cause precipitation. However, t h e latter condition may be carried too far, for if the concentration of acid amounts t o as much as IOO cc. of sulfuric acid of this strength, both t h e chromium and manganese oxidize with greater difficulty and may not oxidize a t all. THE
OXIDXTIOK
OB C H R O M I U M A N D T H E E F F E C T O F
B O I L I N G W I T H H Y D R O C H L O R I C ACID
I n order t o test t h e usefulness of t h e method for t h e oxidation of chromium, solutions containing varying quantities of potassium dichromate and z cc. of N / I O potassium permanganate solution were reduced with an excess of ferrous sulfate in the presence of 30 cc. sulfuric acid (sp. gr. 1.40). T h e excess of ferrous iron was oxidized b y heating with I j drops of concentrated nitric acid. The solution, now containing a known weight of chromium with some ferric salt and manganese, was diluted t o 300 cc. and treated with I O cc. of dilute silver nitrate solution and j g. of ammonium persulfate as usual. After boiling I O min., j cc. of hydrochloric acid ( I t o 3) were added and the solution boiled j min. longer. The solution was then cooled and titrated electrometrically. TABLE IV-DETERMINATIOKOF CHROMIUM
I N THE PRESENCE OF MANGANESE 0.0022 G. Manganese Added in S a c h Case Chromium Taken ( G . ) .. , . . . . . , . . . . , . . . . . . . 0,0102 0.0203 0.0404 Chromium Found ( G . ) .. . . , . . . . . . . . . . , , , , , , . , 0.0101 0.0203 0.0403
,:
The few figures given in Table IV are sufficient t o illustrate t h a t the oxidation of chromium by ammonium persulfate and silver nitrate is a quantitative process and t h a t hydrochloric acid effectively reduces t h e manganese oxidized a t t h e same time without reducing t h e chromium. OBSERT'ATIOSS C O K C E R X I S G T H E E L E C T R O M E T R I C T I T R A TION OF CHROlIIUM
The apparatus and method used was identical m-ith t h a t used by Forbes and Bartlett,' except as 1
LOG. CZl
T H E JOL-R,VAL O F I . V D C S T R I d L A-VD ELVGILVEERIATGC H E i M I S T R Y
Aug., 1916
noted in our paper on the determination of vanadium I n titrating pure chromate solution with ferrous sulfate, we noted the anomalous rise first observed b y Forbes and Bartlett. Thus on setting t h e needle of t h e galvanometer on. t h e middle of the scale and adding ferrous sulfate, a retrograde motion of t h e needle began a t once, continuing until it had covered about seven divisions on t h e scale. The movement became less and less as more ferrous sulfate was added until just before t h e end-point was reached, when it remained stationary until a slight excess of ferrous sulfate caused it t o move rapidly in the direction opposite t o t h a t in which it had been moving. As soon as enough dichromate solution had been added t o cause t h e needle t o return t o its stationary position t h e titration was considered completed. I t was noted early in t h e course of these experiments t h a t t h e anomalous rise in potential either was absent or was much less marked in solutions which had been treated with a n oxidizing agent, such as ammonium persulfate. During the titration of t h e solution of a sample of steel which had been so oxidized, the needle remained within a few divisions of t h e original point during t h e addition of t h e first portions of ferrous sulfate, and would remain absolutely stationary during t h e addition of the last portions, when a n excess would produce a decided movement. Ferric iron likewise seemed t o inhibit this phenomenon. I n one instance, a solution of chromium sulfate, after oxidation with potassium permanganate, was boiled with ammonia t o decompose t h e permanganate. T h e solution so obtained, when filtered t o free it from manganese dioxide, showed no anomalous rise on titrating. Our limited investigation of this point leads us t o believe t h a t amounts of oxidizing agents other t h a n chromate, which are too small in amount for detection otherwise, are effective in suppressing this anomalous behavior of the cell. T H E E F F E C T O F F E R R I C I R O K O N T H E ACCURACY O F T H E TITRATION
Having noted t h a t ferric salts interfered with t h e anomalous rise, we became interested t o know how these salts would affect t h e titration if they were present in large amounts. Accordingly, solutions containing I , z and 3 g. of ferric iron were prepared a n d known quantities of chromium added. Each solution had a volume of 250 cc. and contained 2 5 cc. of sulfuric acid (sp. gr. 1.40)and 0.02j3 g, of chromium as chromate. The ferrous sulfate solution was of such strength t h a t one drop was equivalent t o o.ooooj g. of chromium. I n Table Y the
721
fore and after the end-point. After t h e final throw of t h e needle, enough potassium dichromate solution was added t o cause the needle t o return t o the endpoint and two drops additional. The experiments recorded in Table V indicate t h a t the end-point is as sharp for large amounts of chromium as for small amounts (cf. electrometric titration of vanadiuml), b u t is much affected by t h e presence of ferric salts, especially as regards the anomalous rise. T h a t t h e amount of change for a given increment of ferrous salt would be less in the presence of a large amount of ferric iron would be expected from a consideration of the ferric-ferrous potential, although we should not expect the differences t o be so large as those found. The expression,2 RT Fefff 7r = 0 . 9 8 8 -~ In -__ F Fet+ gives the value of t h e potential which is established when t h e first drop of ferrous iron in excess is added. ,4 given amount of ferrous iron will obviously produce a greater change in t h e value of 7r when t h e concentration of F e + + + is small t h a n when it is large. The effect upon t h e anomalous rise cannot be so readily explained. The differences observed in t h e above experiments show t h a t there might be a tendency t o add more ferrous sulfate when titration is made in the presence of large amounts of ferric salt, but if the titration is carefully made the end-point is t h e same.
+
T H E SESSITIVENESS OF T H E END-POINT
I t seemed possible t h a t while our method of noting the potential change was simpler t h a n t h a t used b y Forbes and Bartlett, perhaps i t was less sensitive. T o test this point we diluted our solutions t o ten times the volume and made titrations with these. The original solutions of potassium dichromate contained 0 . 0 0 1 g. of chromium per cc. The diluted solution therefore contained 0.0001 g. per cc. I n working with this and a n equivalent solution of ferrous sulfate we had no difficulty in making duplicate titrations on 30 cc. of solution within 0.30 cc. This corresponds t o a n error of o.oooo33 g. I t would thus appear t h a t our apparatus was sufficiently sensitive for practical purposes. ACID C O N C E K T R A T I O N A N D T H E E F F E C T O F C H L O R I D E S
Numerous experiments on t h e titration of chromium in steel failed'to show a n y effect of temperature on t h e accuracy or position of t h e p d - p o i n t . The acid concentration should be quite high, particularly in t h e presence of chlorides, as it prevents irregular movements of the needle. Our experiments on the titration in t h e presence of chlorides showed t h a t T A B L E\'-EFFECT OF FERRIC IRON ON THE TITRATION small amounts were without effect, intermediate GRAMS IRON GALVAXOMETER CHAKCES AFTER quantities gave irregular results, but cold solutions Added as GRAx -SUCCESSIVE DROPSFeSO1-AKOMALOUS Ferric CHROMIUM Total RISE BEFORE containing large amounts of hydrochloric acid gave Alum Taken Found 1 2 3 4 5 ( 2 cc.) END-POIST None 0 . 0 2 5 3 0 . 0 2 5 3 0 1 3 4 4 12 7 dirisions excellent titratidns. I 2 3 None
0.0253 0.0253 Kone 0,0051
0,0252 0.0252 hTone ,
.
0 0
0
0.5 0.5
..,
2
2 2
,
,
,
2.5
3 3 2 3 h-one 3 3
8.5 7.5
10:s
2 divisions None I division Seyeral divisions
change of reading of the galvanometer is shown for each drop of ferrous sulfate added immediately be-
T H E TITR.4TION
O F CHRORIIUM A N D V A K A D I U M
Since chromium and vanadium often occur together in steel, the fact t h a t a n y device for oxidizing chromium 1
L O C . Lit.
2
Peters, Z. p h y r i k . Chem., 26 (1898l, 2 0 5 .
T H E J O C R - T A L O F I A V D 1 7 S T R I A LA N D E S G l L V E E R I N G C H E M I S T R Y
722
oxidizes t h e vanadium a t t h e same time, made it necessary t o adapt t h e method t o t h e determination of both elements. When the procedure employed for t h e analysis of plain chromium steel is applied t o the analysis of a solution containing chromium as chromate and vanadium as vanadate: both are reduced by titration with ferrous sulfate. 'The endpoint obtained under these circumstances is less sharp t h a n t h e one obtained when chromium alone is titrated. The end-point observed is really the vanadium end-point, t h e characteristics of n-hich haxye been described elsewhere. T o test t h e accuracy of this titration, known quantities of chromium as chromate solution were mixed with known quantities of 1-anadium. These mixed solutions were reduced with excess of ferrous sulfate and oxidized with nitric acid, silver nitrate a n d ammonium persulfate under the conditions described above. T h e solutions were then boiled with a small amount of hydrochloric acid. After cooling t o 20' C. they mere titrated ele'ctrometrically with ferrous sulfate in a volume of 2 5 0 cc. The chromium was assumed as t h e amount taken, the difference being taken as vanadium. T.4BI.E
VI-TITRATION OF
SOLUTIOXS C O N T A I X I N G BOTIi C H R O M I U M A N D
vAlvADI171f
Chromium Assumed ( G . ) .. . , . , , . , . 0.0203 0,0101 0.0203 Vanadium Taken ( G . ) .. . . . . . , , , . . 0.6255 0 . I000 0.0255 0,1000 0.0255 Vanadium Found ( G . ) .. . . , . . , , , , . 0.0254 0.1001 0.0252 0.1005 0.0247
This titration gives t h e oxidizing value of both chromium and vanadium. -4s t h e percentage of vanadium in steels is often quite low, it is convenient t o take a 3-8. sample for t h e vanadium determination, of which a n aliquot portion may be used for the total chromium and vanadium determination. T H E APPLICATION O F T H E METHOD TO T H E DETERMIKATION O F CHROYIUM AND VAKADIUM I S STEEL
I K T H E A B S E S C E O F VAKADIUM-A I-g. sample of steel is dissolved in 6 0 cc. of sulfuric acid (sp. gr. I . 2 0 ) , evaporated until salts separate, diluted t o a rolume of 6 0 cc. and while still hot oxidized with dilute nitric acid. Evaporation until salts separate is recommended here as a device for breaking up carbides: t h e completeness with which this has been accomplished may usually be judged by an examination of the diluted solution, for, if carbides remain undestroyed, a more or less well marked turbidity, possibly accompanied by clearly visible: dark particles, will be noted: when this method fails t o break u p carbides, a more vigorous attack may be had b y dissolvihg in 60 cc. of dilute hydrochloric acid (sp. gr. I , I j ) after which the solution should be oxidized with nitric acid; this solution, however, must be evaporated with 60 cc. dilute sulfuric acid t o the appearance of fumes t o give complete separation of hydrochloric acid. However prepared, t h e solution (containing t h e equivalent of 6 0 cc. sulfuric acid of sp. gr. I . 20) should be diluted t o a 7-olume of 300 cc. and heated t o boiling. T o t h e boiling solution are then added I O cc. of a solution of silver nitrate containing 2.6 g. per liter and j g. ammonium persulfate, conveniently used in the form of a solution containing j o g. of the salt in a rolume of z j o cc. PROCEDURE
1-0;.6 , No. 8
The solution is boiled vigorously for I O min., a f t e r which j cc. dilute hydrochloric acid ( I : 3 ) are added and the boiling continued for j min. .%fter cooling t o a convenient temperature and the addition of a little more sulfuric acid, the solution is ready t o titrate electrometrically. It is generally possible t o tell if the process has failed a t any point by certain readily noted signs. Thus t h e failure t o break u p carbides may be noted by examining t h e solution. If the solution contains chlorides which would interfere with the catalysis of the ammonium persulfate oxidation by the silver nitrate, a precipitate of silver chloride ill appear. If t h e oxidation of the chromium is unsatisfactory, t h e deep red color of the permanganic acid will fail t o appear. If the decomposition of the permanganic acid with hydrochloric acid is incomplete, t h e solution will not have a clear yellow color. The chief pitfalls into which t h e analyst may fall are, ( I ) incomplete breaking u p of carbides of chromium, ( 2 ) incomplete oxidation of chromium due t o high concentratioii of acid. precipitation of silver or the presence of too little ammonium persulfate, (3) failure t o remove all of the products of t h e decomposition of t h e oxidizing agent (which may be accomplished by boiling I O min.), and ( 4 ) failure t o remove t h e chlorine liberated by t h e action of hydrochloric acid on the permanganic acid for which j min. boiling is necessary. PROCEDURE
IK
THE
PRESEKCE
OF
VAKADIUM-A
z or 3 g. sample of steel is dissolved as in the above procedure, using u p t o I O O CC. of dilute sulfuric acid where this is necessary. The solution is diluted t o zoo cc., heated t o 80' C., and after the addition of j g. of sodium phosphate, is titrated with N/IO potassium permanganate until the first "gray" color appears. The solution is then cooled t o I O to z o o C. by adding ice, and more sulfuric acid is added, when it is ready for t h e electrometric titration with ferrous sulfate. +Lifter t h e titration, t h e stirrer and t h e electrodes are rinsed into t h e solution. which is then made u p t o definite volume and a portion representing I g. of the steel is taken for the chromium determination. This portion is diluted t o 300 cc., heated t o boiling and otherwise treated as described under t h e procedure for chromium, except t h a t before t h e titration with ferrous sulfate, the solution should be cooled thoroughly. The amount of chromium present is calculated from t h e amount of ferrous sulfate used, as corrected for t h e amount of vanadium present and the amount of chromium used in finding the endpoint in this and t h e previous titration. T\7hen tungsten is present the precipitate of WOS makes it difficult t o deal with t h e carbide present. The addition of j g. of sodium phosphate, as suggested by Wdowiszewski,' by keeping t h e tungstic oxide in solution, makes this much easier. The fact t h a t potassium permanganate will oxidize chromic salts in hot acid solution causes t h e end-point obtained by oxidizing with this reagent t o be somewhat fleeting. Csually the end-point is \-isible for z min. I n genera!, there is very little difficulty in find1
Chem.-Ztg., 34, 1365.
Aug., 1916
T H E J O I ’ R N A L O F I N D C S T R I A L AiVD E X G I X E E R I N G C H E M I S T R I ‘
ing t h e end-point if the solution is hot ( i o t o 8 0 ” C . ) , fairly dilute (zoo cc.) and the chromium content is not too high. The addition of some sodium phosphate prevents interference from t h e yellow color of t h e ferric iron, b u t green chromic salt is t h e main cause of difficulty. T h e first change of color which appears (from green t o “gray”) should be t a k e n as t h e end-point. If too much permanganate is added, a few drops of ferrous sulfate may be added and the end-point sought again. TABLEVII-ANALYSIS
OB
SAMPLES OF STEEL FOR CHROMIUM AND
tions of the East. The ,result of the investigation of t h e pomace wines has been very gratifying and it has enabled us t o recogndze this product with assurance. Having’ received f r o m 1-arious sources urgent and repeated requests for t h e information obtained from this work the author feels this demand a sufficient reason for its publication. For the benefit of those who are not acquainted with the manufacture of pomace wines a brief outline of the processes used is included in this paper with the hope t h a t it will aid in interpreting t h e results.
VANADIUM
I Private Standard ‘2 3 4 5 6
I-GRAPE
.. .. ..
7
s9 10 11 12 13 14
..
.. ..
15
0 :i3 0 : i3
16 li 18 19 20
.. ..
0.26 0.53 1.04 1.57 2.55 2.55 2.55
0.26 0.52 1.03 1.55 2.58 2.58 2.58
.. .. ..
..
..
.. .. ..
..
.. .. .. ..
.. ..
32 32 32 32 31 31 31 31 34 34 34 34 10(b) IO@)
..
.. ..
..
..
16:~) 30 30 30
..
o:i1 0.21 0.21
..
.. ..
0’20 0.20 0.20
The results given in Table VI1 were obtained by using t h e procedure given above. Besides t h e standards issued b y the Bureau of Standards, a standard prepared in this laboratory, having a chromium content of I . 46 per cent, was analyzed with and without varying amounts of added chromium, manganese and vanadium. RESEARCHDEPARTMENT, THE LMIDVALESTEELCOMPAKY PHILADELPHIA
POMACE WINES: THEIR COMPOSITION AND DETECTION1 By
JOHN
R.
EOFF,JR.
Received April 21, 1916
Desiring some information on the composition of various types of American wines, the laboratory of the Internal Revenue Bureau undertook in 1913-14 t h e collection and analysis of a large number of these wines, and it particularly desired t o ascertain the composition of the so-called pomace .wines, a t t h a t time being rather extensively manufactured in certain sec1
Published by permission of the Commissioner of Internal Revenue.
723
POMACE
For t h e purposes of this article, grape pomace m a y be defined as t h e residue of the grape after the juice has been partially or thoroughly removed, before o r after fermentation. Pomace may be divided into t w o main divisions-white and red. ( a ) WHITE POMACE-This pomace is almost invariably t h a t from the Catawba grape. The grapes are ground and t h e juice pressed from the skins, seeds and pulp, t h e juice so obtained being fermented separately. The residue (pomace) can never be pressed entirely free of juice and often contains as much as 8 per cent sugar. Sometimes the pomace is immediately used for pomace wine, b u t oftener i t is packed tight into barrels and allowed there t o ferment. The length of time t h e pomace is kept in barrels before use varies from a few weeks t o a year or more. ( b ) R E D POMACE-The principal grape from Lvhich this pomace is derived is the Concord. T o a lesser extent Concord and Ives mixed furnish this t y p e of pomace, and though in this investigation there is no record of them, the writer has seen used t h e heavier colored varieties such as Norton and Clinton. The red pomace is obtained in three ways: ( I ) I n making red wines the grapes are ground and the whole mass-juice, skins, pulp and seeds-is allowed t o ferment, and a t the proper stage t h e new wine is pressed off and the pomace packed in barrels; ( 2 ) instead of pressing off the wine t h e pomace is sometimes alrowed t o drain and, without pressing, immediately used for wine: this procedure is infrequent; ( 3 ) in t h e manufacture of red grape juice the fruit is crushed, t h e mass heated to about I j o O F,,and then pressed. 11-POMACE
WINES
For t h e purposes of this article. pomace wine may be defined as t h e product obtained b y the alcoholic fermentation of sugar solution upon grape pomace. accompanied b y the usual cellar treatment. T h e Commissioner of Internal Revenue1 has held t h a t t h e manufacture of pomace wine is prohibited b y Section 3 2 8 2 , U. S. Revised Statutes, “except in a building or on premises of a distillery duly authorized according t o law.” G E i i E R A L >I E T H 0 D 0 F 31 -4K UE A CT T R E- -A quantity of pomace ranging from 6 j o t o I j o o lbs., according t o quality of pomace and product desired, is placed in open fermentation vats of sufficient capacity, and updn this are run 700 t o 800 gals. of “sugar water,” t h e mash being yeasted or not, as conditions require. The “sugar water” is prepared from cane or corn sugar 1
Treasury Decision 1949, 2#’16:14.
