Oct., 1921
THE JOURNAL OF INDUSTRIAL AND ENGINEERING CHEMISTRY CONCLUSIONS
The chemical characteristics of soda and sulfate pulps indicate that they are a very pure form of wood cellulose and capable of high yields of white fibrous and resistant material. The sulfate process is much more efficient than the soda process in yielding a bleachable pulp from coniferous wood. The coloring matter in pulps is of the nature of a dye and can be removed without materially reducing yields. Most of the action in cooking to reduce bleach consumption is to dissolve and degrade the cellulose.
939
Modifications in bleaching methods give promise of greater result,s than modifying cooking methods. Modifications in which the bleaching operation was divided into two steps, with washing between steps, cut the bleach requirement in two. Pulps of better quality, both from physical and chemical considerations, are obtained by cooking the wood as little as possible in isolating the fibers and by accomplishing as much of the burden of purification as possible in the bleaching and washing operations.
The Determination of Vanadium and Chromium in Ferrovanadium by Electrometric Titration' By G . L. Kelley, J. A. Wiley, R. T. Bohn and W. e. Wright
MIDVALE STEEL &
ORDNANCE
C0.p NICETOWN PLANT,
The object of this paper is to describe a method for the determination of vanadium in ferrovanadium not subject to interference by chromium, which is so often present. Kelley and Conant2 described the electrometric titration of vanadium following oxidation with ammonium persulfate and silver nitrate, but the method did not provide against the possible presence of chromium. Kelley and the collaborators3 above named described a method for the selective oxidation of vanadium in steel in the presence of chromium, using nitric acid as an oxidizing agent. At that time, however, we were not prepared to recommend the application of our procedure to the determination of vanadium in ferrovanadium. Since then its application t o the analysis of this alloy has been studied. PRELIMINARY EXPERIMENTAL WORK DETERMINATION O F VANADIUM I N AMMONIUM VANADATE-
A large volume of solution was prepared from ammonium vanadate described by the maker as C. P. This was analyzed by two methods. I n the first, the vanadium was determined by titrating the solution with ferrous sulfate and dichromate, taking as the end-point the point of greatest change in the oxidation-reduction potential. The potassium dichromate solution was made from a C. P. salt which had been recrystallized and fused. It was also compared through the ferrous sulfate with permanganate which had been standardized against sodium oxalate. The average difference between these standardizations was less than one part in one thousand. I n the second method, 100 cc. of the ammonium vanadate solution were placed in a flask, with an equal volume of water and 5 cc. of sulfuric acid (sp. gr. 1.58); and treated with sulfur dioxide for 20 min. a t the boiling temperature. The excess of sulfur dioxide was removed by passing purified carbon dioxide through the still boiling solution for an additional 20 min. Two hundred cc. of a boiling water solution containing 50 cc. of sulfuric acid (sp. gr. 1.58) were next added, and the mixture was titrated hot with 0.05 N permanganate using the potentiometric end-point. Eight determinations by the first method gave 0.1273 and 0.1274 g. of vanadium in 100 cc. of solution, the average result being nearer 0.1273. The solutions titrated with permanganate after sulfur dioxide reduction did not agree so well. The results ranged from 0.1269 to 0.1275, averaging 0.1272. The condition most favorable t o titration with ferrous sulfate is an acid concentration of about 50 cc. of sulfuric acid (sp. gr. 1.58) in a volume of 350 cc. at a temperature of 5" @. Under these circumstances the change in potential for 0.05 cc. of the ferrous sulfate solution (23 g. ferrous ammonium sulfate in one liter) is about 50 mv. at the end-point. 1 Received
April 13. 1921. A m . Chem. Soc., 88 (Isle), 349. *Tars JOURNAL, 11 (1919), 632.
* J.
PHILADELPHIA, P E N N S Y L V A N t d
When the vanadyl sulfate is titrated at 80" C. with permanganate in a similar acid concentration, the change of potential is about 60 mv. Under these conditions the color of permanganate is not visible until about 0.20 to 0.25 cc. more of the permanganate solution has been added. The poorer quality of the work done with permanganate may be due t s the incompleteness of the reaction between the permanganic acid and vanadyl sulfate, and the results are, doubtless, affected by the exposure of the hot solution to air during titration. NITRIC ACID OXIDATION-The solution of vanadyl sulfate, standardized as above, was used to check further the degree of oxidation effected upon vanadyl salts by nitric acid. 13 our earlier paper on the selective oxidation of vanadyl salts by nitric acid in the presence of chromic salts, it was suggested that the vanadium be considered approximately 99 per cent oxidized. Our more recent work leads to the belief that the degree of oxidation is more nearly 99.5 per cent. With the object of simulating conditions which would obtain if the work were done upon ferrovanadium, solutions were prepared containing 0.3 g. of pure iron, 0.1273 g. of vanadium as ammonium vanadate, 25 cc. of sulfuric acid (sp. gr. 1.58), 40 cc. of nitric acid (sp. gr. 1.40), and water enough to make the total volume 200 cc. The iron was first dissolved in the sulfuric acid and water in the presence of the ammonium vanadate, thus reducing the latter to vanadyl sulfate. The mixture was boiled for 1 hr., a t such a rate that the volume was 100 cc. at the end of the period. It was then cooled to 5" C. and titrated electrometrically with ferrous sulfate and potassium dichromate. Out of twenty-four determinations made, the value found for percentage oxidation was 99.3 in four cases, 99.5 in eleven, 99.6 in six, and 99.7 in three. The average was 99.5 per cent oxidation, with a maximum variation of 0.2 per cent above and below. We have previously shown' that chromium is not oxidized under these conditions. We have made a further investigation of the effect of conditions upon the oxidation of vanadium by nitric acid, but inasmuch as our results were largely negative, they need not be described in detail. Oxidations conducted in flasks a t the boiling temperature, with air passed through for 6hrs., did not show consistently higher oxidation than solutions boiled 1 hr. in beakers covered with watch glasses. When air was excluded, the results were slightly lower. METHODFOR DETERMINING CHROMIUMAND VANADIUM IN FERROVANADIUM Dissolve 3 g. of ferrovanadium in 75 cc. of nitric acid (sp. gr. 1.13). When solution is nearly complete, add 10 cc. of hydrochloric acid (sp. gr. 1.20). When the amount of silicon is large, i t may be convenient to add a few drops of 1 LOG.
ci).
940
T H 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
hydrofluoric acid to bring about solution. Next add 50 cc. of sulfuric acid (sp. gr. 1.58) and evaporate until fumes appear, to remove nitric and hydrochloric acids, and to complete the decomposition of vanadium carbides. The insoluble residue after this treatment is generally small and consists chiefly of aluminium oxide. Ordinarily no loss of vanadium occurs if i t is disregarded, but i t may be dissolved in water after fusion with sodium peroxide. The alkaline solution so obtained should be boiled for at least 15 min. to remove hydrogen peroxide. The solution may then be acidified with a slight excess of sulfuric acid and added to the main filtrate. This solution is then cooled and made up to a volume of 1000 cc. One hundred cc. portions of this solution. corresponding to 0.3 g., are convenient quantities for subsequent work. DETERMINATION OF VANADIUM AND CHROMIUM-TO a 100-cc. portion add 25 cc. of sulfuric acid (sp. gr. 1.58) and water enough to make the volume 300 cc. Heat the solution to boiling and add 20 cc. or more of a 10 per cent solution of ammonium persulfate and 10 cc. of a 0.25 per cent solution of silver nitrate. Boil the solution a t least 10 min. to oxidize the vanadium and decompose the excess of ammonium persulfate. If there is no manganese in the ferrovanadium, some should be added, as the persistence of the color of permanganic acid is a good indication that the amount of ammonium persulfate added has been sufficient to complete the oxidation of all chromium and vanadium. After 10 min. boiling, add 5 cc. of hydrochloric acid (1 : 3), and continue the boiling 5 or 10 min. longer. I n this way the permanganic acid is completely destroyed without reducing either chromium or vanadium. After the addition of a further 25 cc. of sulfuric acid and cooling to 5" C., the solution may be titrated electrometrically. It is convenient to use for the titration the solutions used in titrating chromium in steel. As described in the previous paper, these are made by dissolving 2.828 g , of potassium dichromate in water to make 1000 cc., and by dissolving 23 g. of ferrous ammonium sulfate and 100 cc. of sulfuric acid (sp. gr. 1.58) in enough water to make 1 liter. The dichromate solution is used for reference and the ferrous sulfate solution compared with it electrometrically a t the time the work is done. When a high degree of accuracy is desired and the conditions under which the work is carried out require it, the dichromate should be purified and fused before weighing. Each cubic .centimeter of this dichromate solution is equivalent to 0.001 g. chromium or 0.002943 g. vanadium. When the ferrovanadium oxidized as described above is titrated with ferrous sulfate and dichromate, both chromium and vanadium are titrated. Multiplying by 2.943 and dividing by 3 gives the apparent percentage of vanadium, which includes both vanadium and chromium. DETERMINATION OB VANADIUM-The vanadium is determined in a separate 100-cc. portion. During the evaporation of the nitric acid solution with sulfuric acid, a slight oxidation of chromium may have occurred. It is, therefore, desirable to add a few cc. of ferrous sulfate solution to reduce this. After a few minutes boiling, add 20 cc. of sulfuric acid (sp. gr. 1.58), and 40 cc. of nitric acid (sp. gr. 1.40), together with enough water to make the volume 200 cc. Place a label on the beaker marking the 100-cc. level, and boil at such a rate that the volume is reduced to 100 cc. in 1 hr. Dilute the solution with ice water and cool to 5 O C. to titrate. Divide the titration result by 995 and multiply by 1000. Divide the product by 3 and multiply by 2.943. This gives the actual percentage of vanadium. CHROMIUM BY DIFFERENCE-BYsubtracting the actual percentage of vanadium from the percentage representing both chromium and vanadium we obtain a figure corre-
Vol. 13, No. 10
sponding to chromium but expressed in terms of vanadium. Dividing this by 2.943 gives the percentage of chromium. The use of the factor 2.943 may be avoided if 2.883 g. of potassium dichromate are used to prepare the solution. I n this case each cc. corresponds to 1 per cent of vanadium when the sample titrated contains 0.3 g. of the ferro-alloy. APPLICATION OF METHOD The application of this method to the analysis of two samples of ferrovanadium known to contain chromium gave the following results: -as
Chromium and Vanadium Vanadium--
SAMPLE Per cent Average A 41.29, 41.32, 41.34 41.32 B 48.29, 48.36 48.32
-VanadiumPer cent Average 33.05,33.13,33.09 33.09 43.30,43.36,43.40 43.35
By calculation from the averages, Sample A contained 2.80 per cent of chromium, and Sample B contained 1.61 per cent. To check the accuracy of this method of determining chromium in ferrovanadium, a procedure which separated most of the vanadium was devised. It had the advantage of permitting work with a much larger amount of chromium in the presence of a greatly diminished percentage of vanadium. For this purpose 1-g. samples of ferrovanadium were dissolved in hydrochloric acid (sp. gr. 1.10)) and oxidized with nitric acid. The solution was evaporated to a sirupy consistency, when a second portion of hydrochloric acid was added and the evaporation repeated. Iron was extracted from this with ether, and the aqueous solution evaporated with sulfuric acid until fumes appeared. It was then diluted to 160 cc., and 40 cc. of nitric acid (sp. gr. 1.40) were added. Boiling this solution under the prescribed conditions oxidized nearly all of the vanadium and no chromium. To the cool solution, sodium carbonate was added to precipitate iron and chromium, along with some manganese and a small amount of vanadium. The precipitate was washed and dissolved in nitric acid and a little water. The resulting solution was made up to a volume of 200 cc. after the addition of 40 cc. of nitric acid (sp gr. 1.40), and 25 cc. of sulfuric acid (sp. gr. 1.58). After a second oxidation of vanadium by boiling, the chromium was again precipitated. This precipitate still contained vanadium, but only in avery smallamount. It could have been completely removed by oxidizing the chromium with ammonium persulfate and precipitating the vanadium with uranium, as described elsewhere by US.^ This did not seem necessary, and we, therefore, resorted to the easier procedure of determining the amount of vanadium present. The vanadium in the precipitate was oxidized with nitric acid in the usual way, and titrated with ferrous sulfate. The amount of vanadium so found varied with different samples, but averaged about 0.4 per cent, After titrating the vanadium, each solution was evaporated until sulfuric acid fumes appeared, after which i t was diluted and both vanadium and chromium were oxidized with ammonium persulfate. The amount of chromium waslarge enough to require about 17 t o 30 cc. of our ferrous sulfate solution for its titration, thus permitting a very accurate determination of combined chromium and vanadium. By subtracting the vanadium previously determined on each portion from the total of chromium and vanadium, new figures were obtained for the chromium present. I n Sample A: chromium was found as 2.79, 2.77, and 2.77 per cent, which is in good agreement with 2.80 found by the f i s t method. Sample B gave 1.62,1.61, and 1.59 per cent, against 1.61 previously found. SUMMARY 1-The authors have confirmed the identity between the electrometric end-point value obtained by titrating vanadium with ferrous sulfate and by titrating pure solutions 1
THISJOURNAL, 11 (1919), 632.
THE JOURNAL OF INDUSTRIAL AND ENGINEERING CHEMISTRY
Oct., 1921
of vanadyl sulfate with permanganate when suitable blanks w e used in the later titration. 2-It is demonstrated that the oxidation of vanadium by nitric acid under a fixed set of conditions gives a very regular degree of oxidation. 3-It has been previously shown that chromium is not oxidized under the conditions described. 4-A method has been developed for the determination
94 1
of vanadium in ferrovanadium containing chromium. &The authors have shown that the amount of chromium can be determined with accuracy from the difference between the titrations after oxidation with silver nitrate and ammonium persulfate and after oxidation with nitric acid. 6-Results have been given showing the chromium obtained after separating nearly all of both vanadium and iron.
Effect of Variation in Analytical Constants of Linseed and Soy-Bean Oils upon the Quantitative Determination of Linseed Oil in Mixtures of the Two Oils by Means of the Iodine and Hexabromide Numbers of the Fatty Acids' By Edward A. Tschudy 8,I.
DU P O X T DE
XSMOURS 82 CO.,PHILADELPHIA, PENNSYLVAXIA
I n a recent paper2 Bailey and Baldsiefen have published results for the quantitative determination of linseed oil in mixtures of linseed and soy-bean oils, by a modified method for the determination of the hexabromide number of the fatty acids. It is possible, from the results there enumerated, to show the relation existing between the iodine numbers and the hexabromide numbers of the fatty acids of such mixtures, and to ascertain the error introduced into a determination when oils having constants differing from those used by Bailey and Baldsiefen in their investigation occur in mixtures, the iodine or hexabromide numbers of which are compared with Tables I11 or IV of their paper to ascertain the percentage of linseed oil present in the mixtures. RELATIONBETWEEN IODINE NUMBERAND PERCENTAGE OF LINSEEDOIL IN MIXTURES By plotting the iodine numbers of the mixtures in Table I11 (Bailey and Baldsiefen) against the per cent of linseed oil (Graph I), the plotted points lie on a straight line, the general equation of which is X-b
=
7.
For this case, y is the per cent of linseed oil in the mixture, b is the iodine number of the pure soy-bean oil in the mixture, x is the iodine number of the mixture, and m is the cotangent of the angle which the line makes with the x-axis. The iodine numbers of the oils used by Bailey and Baldsiefen in their work have not been recorded, but the linseed oil used probably had an iodine number of 179, and the soy-bean oil an iodine number of 135.5. Substituting these constants in the general equation it becomes X-
=
135.5 0.435 '
(1)
This can be shown by substituting in Equation 1 the per cent of linseed oil present in the mixture and computing the corrected iodine number, as tabulated. R~~~~~~~BETWEEN H~~~~~~~~~~N~~~~ OF THE pAmY ACIDS AND THE PERCENTAGE OF LINSEED OILIN THE MIXTURES BY Plotting the hexabromide numbers of the fatty acids in Table IV (Bailey and Baldsiefen) against the Per cent of linseed-od Present in certain mixtures designated as Samples
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30
60 5ro /PO ~e.?&bI-~?m& i&Jne NQS.
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793 to 811 (Graph 11))the plotted points lie on a straight line Comparing the calculated values for the per cent of linseed similar to the iodine number-linseed oil curve, and have a oil in the mixtures wit$ the per cent actually present, by similar general equation. For this line y is the per cent of substituting the determined iodine numbers in Equation 1, linseed oil in the mixture, x is the hexabromide number of the we find: fatty acids, b is the hexabromide number of the pure soy-bean MIXTURE oil in the mixture, and m the cotangent of the angle made by -Linseed OilLinseed Soy-Bean Oil Oil -Iodine NumberPresent Calculated Percentage the line with the x-axis. The linseed oil used by Bailey and Per cent Per cent Determined Corrected Fer cent Per cent Difference Baldsiefen in their mixtures had a hexabromide number of 42, 85 15 171.9 172.5 85 83.8 -1.2 75 25 168.0 168.1 75 74.7 -0.3 while the soy-bean oil had a hexabromide number of 6. Sub65 35 164.2 163.8 65 66.1 stituting these constants in the general equation it becomes: 50 50 ... 157.3 50 ... ... The differencebetween the calculated percentage of linseed y=- X-6 oil in the mixtures and the percentage actually present is very (2) 0.36 small, and within the limit of experimental error, which, for the iodine number, is usually * 0.5 unit. By substituting the determined hexabromide numbers of the prepared oil mixtures designated Samples 793 to 811 in 1 Received April 18, 1921. Equation 2, the following results are obtained: *TEIS JOURNAL, 12 (1920),1189.
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