Jan., 1912
T H E JOL-R-YAL OF IlYE U S T R I A L A X 0 EATGIiVEERIArG C H E M I S T R Y .
who takes exceition to. this view, arguing t h a t the pentoxide would be reduced a t the glass-making temperature. Rosenhain, author of “Glass Manufacture,” supports the latter opinion, and adds t h a t he believes very little arsenic remains in the glass a t all. It seemed of interest, therefore, t o study this question from. the analytical standpoint, b y examination of the glass itself. Some unexpected results were obtained. Two varieties of glass were analyzed for arsenic: SO. I , a soda-baryta glass, of fairly high alkali-cont e n t ; S o . 2 , a potash-lead glass, used for cut-glass ware. I n So. I , the arsenious oxide put into the batch, or raw materials, was between 0 . 3 and 0.j per cent. of the glass produced, while in No. 2 i t was approximately 0.45 per cent. I n both these batches, potassium nitrate xi-as used in considerable quantity, and in N o . 2 red lead was one of the main ccmstituents, so t h a t there was abundant opportunity for the initial oxidation of the arsenic t o the pentavalent condition. The method used for determining the percentage and state of oxidation of the arsenic remaining in the glass was as follows: Samples of glass, powdered t o pass a 40-mesh sieve, were weighed into a platinum dish and treated with 15-20 cc. of hydrofluoric acid, added in three portions. When reaction had ceased, 20 cc. of 30 per cent. sulphuric acid were added, and the mixture evaporated on a water-bath until hydrofluoric acid fumes ceased coming off. It was then rinsed into a beaker, making a total volume of 40 cc., and arsenic acid determined b y titration after the manner described in Sutton’s “Volumetric Analysis.” I n the case of the lead glass, the solution was filtered before the addition of potassium iodide, t o remove the lead sulphate and avoid formation of lead iodide. After titrating with thiosulphate, the solution was nearly neutralized with sodium carbonate, 2 0 cc. of a saturated solution of sodium bicarbonate were added, the arsenious acid was titrated with iodine, and the arsenious oxide originally present determined b y difference. The standard solutions used were twentieth-normal. Blank determinations showed t h a t the reagents contained no measurable quantity of arsenic. The data obtained are tabulated below. cc. s / 2 0 Glass. Grams thio- Cc. .\’/20 No. sample. sulphate. iodine. 1 1 2 2 2’
6.60 4.82 4.25 7.73 6.00
9.0 4.2 5.9 9.6 8.6
9.1 5.1 6.6 9.6 8.6
Per cent As205.
0,02587 0,01207 0,01696 0,02760 0,02472
As203
0.0003 0,0022 0,0017 0.0000 0,0000
Per cent.
4 ~ ~ 0 As201 j 0 0 0 0 0
39 25 40 36 41
0 00 0.05 0.04 0.00 0 00
These results indicate that a great part of the arsenic used in glass-making remains in the glass as the higher oxide, probably as arsenate of soda or potash. This is somewhat surprising, in view of the properties attributed t o arsenic in justification of its use. I t is expected t o volatilize, aiding in the mixing of the batch as the latter melts. Moreover, it is said to have a n oxidizing effect, but the fact t h a t the arsenious Sample fused with sodium carbonate-and dissolved jn sulphuric acid.
17
oxide originally employed appears finally in the glass with a gain of oxygen does not bear out this belief. On the contrary, i t seems t h a t the use of arsenic must reduce the available oxygen of the batch. At least in cases where nitrates are present and the melting carried on in closed pots, as in the manufacture of the glasses here examined, the value of the arsenic, if any, obviously lies in neither its volatilizing nor its oxidizing powers. The glass used and the data concerning i t were furnished b y one of the glass companies of this vicinity. LABORATORY O F INDUSTRIAL RESEARCH, UNIVERSITY OF PITTSBURGH, P ITTSBURGH .
THE DETERMINATION OF CHROMIUM AND ITS SEPARATION FROM VANADIUM IN STEELS. By J. R . CAIN. Received November 10, 1911.
While attempting, recently, t o determine chromium in chrome-vanadium steels, difficulties with some of the usual methods were encountered. If a steel containing chromium as chromate and vanadium as vanadate is titrated against ferrous solutions, using ferricyanide t o indicate the point a t which all the vanadium and chromium are reduced and an excess of titrating solution is present, there is sometimes a n indefinite end-point, because as soon as some vanadium is reduced t o the vanadyl condition this reacts with the ferricyanide indicator, reducing it to ferrocyanide which then gives the usual color with the ferric salts present.‘ An experienced operator can oftentimes judge the end-point sufficiently closely for practical work, b u t the difficulty increases with increasing vanadium, and it is almost always necessary t o run blanks of various kinds, increasing t o t h a t extent the uncertainties of such methods. If the excess of ferrous solution is titrated back with permanganate some correction is also necessary for chromium oxidized by permanganate.* If in the preliminary oxidation of the vanadium and chromium, any manganese dioxide separates, as where potassium permanganate or potassium chlorate are used, some chromium may be, and often is, carried down b y the manganese.3 If, in order t o separate vanadate from chromate, the nitric acid solution of the steel (with or without preliminary ether extraction of most of the iron) is poured into excess of sodium hydroxide solution and boiled, usually a n appreciable amount of chromium goes into the filtrate with the vanadium. Many methods take no account of this chromium. The amount so lost increases with the manganese in the steel and the time of boiling, the manganese being converted in part t o peroxide and this, in the strongly alkaline solution, oxidizing the chromium t o chromate.4 Many careful tests having shown t h a t chromium in Cain, THISJOURNAL, 3,476 (1911) ; other references will be found here. Cain. loc. cit. a Arnold and Ibbottson, “Steel Works Analysis,” 3rd Ed., P. 180. also Cain, loc. cit. 4 Cain, loc. c i t . 1
2
T H E J O U R N A L OF I N D U S T R I A L AhlD ENGINEERIA'G C H E M I S T R Y .
IS
much larger amount than the usual commercial steels carry can be precipitated completely in a few minutes b y boiling the nearly neutralized (ferrous) solution of the steel with barium carbonate, cadmium carbonate, zinc oxide or magnesium oxide, it was decided to base a method for determining chromium on one of these methods of separation from iron. Probably the reason why such separations have not come into more general use is because practically all writers have directed to make the carbonate or oxide precipitation in the cold, which requires many hours' standing and is even then sometimes incomplete. The work done here has shown that but ten or fifteen minutes' boiling, with proper precautions, is all that is ever necessary, the filtrates being free from even traces of chromium (or vanadium). Noyes and Bray' have given conditions for completely precipitating chromates in the presence of vanadates which make possible a good separation of the two elements. The work here having completely confirmed their results, this separation was incorporated in the method. DESCRIP,TION OF T H E M E T H O D .
Dissolve in a covered 300 cc. Erlenmeyer flask a n amount of drillings, which will give not to exceed 6 or 7 centigrams of chromium, using about I O cc. of concentrated hydrochloric acid per gram of steel. The concentrated acid (specific gravity 1.20) seems to dissolve the steel much more readily than a diluted acid. When no more hydrogen is given off, dilute t o I O O or 1 5 0 cc. with hot water, nearly neutralize with saturated sodium carbonate solution, add barium carbonate emulsion in slight excess, place on the hot plate and boil vigorously ten or fifteen minutes, with small additions of the barium carbonate emulsion every two or three minutes. The flask should be kept covered during all operations so as to exclude air as completely as possible. Too great a n excess of barium carbonate should not be used, as this increases the difficulty of extracting the chromium in the subsequent fusion. An excess of a gram or two is the most that should be present. Remove the flask from the plate, let the precipitate settle, and filter a t once on a 1 1 cm. white label No. 589 filter, washing twice with hot water. These operations should be carried out rapidly and without delay. Place the filter and precipitate in a sufficiently large platinum crucible, burn off the filter, add 2 grams of sodium carbonate and about gram potassium nitrate, and fuse for 2 0 minutes. Support the inverted and inclined crucible on a glass triangle which has glass legs about J/, inch long fused t o its corners for supports, place on the bottom of a 2 5 0 cc. beaker, cover it with boiling water and digest a few minutes until the fusion is disintegrated. Filter into a flask, add I or 2 cubic centimeters of hydrogen peroxide to the filtrate and boil for five or ten minutes to destroy the excess of peroxide. Cool, transfer t o a 2 5 0 or 300 cc. separatory funnel, add a slight excess of nitric acid (I-I), and shake vigorously a few minutes, allowing the liberated 1 Technology
Quarlerlr. 21. 14 (1908).
Jan.,
1912
carbon dioxide to escape b y inverting the separatory funnel and opening the stopcock. Transfer to a 2 5 0 cc. beaker, just neutralize with sodium hydroxide solution, and then add nitric acid (I-I), 2 cc. for each I O O cc. of solution. Add 2 0 cc. of a 2 0 per cent, lead nitrate solution t o the cold solution, stirring vigorously. The precipitate settles quickly. I t is filtered on asbestos, and washed three or four times with cold water. The asbestos mat is transferred to a beaker or flask, and the lead chromate decomposed with hot hydrochloric acid (1-4). The solution is cooled, the volume made u p t o 1 5 0 or 2 0 0 cc. and i t is titrated against approximately N/IO ferrous sulphate solution with ferricyanide as outside indicator. Or, if desired, an excess of the ferrous sulphate solution is added and the excess titrated back against bichromate. The standard iron solution should be compared with bichromate or permanganate on the day it is used. Table I gives results obtained with synthetic solutions and with the chrome-vanadium standard steel of the Bureau of Standards. The synthetic solutions were made b y adding the chromium from a carefully standardized bichromate solution and the vanadium from a sodium vanadate solution to the hydrochloric acid solution of a vanadium and chromium free steel. TABLEI. No. of expt. 1 2 3 4 5 6 7 8 9'
Iron present. Grams. 1 1 1 1 1 1 1 1 4
Vanadium present. 0.0012 0.0024 0.0024 0.0036 0,0048 0.0060 0.0120 0,0180
..
Chromium present. 0.0140 0.0280 0.0420 0.0560 0.0700 0.1120 0.1680 0.2800
..
Chromium found. 0.0137 0.0277 0.0420 0,0558 0.0700 0.1122 0.1685 0.2805 0,0536
Difference. -0.0003 -0.0003 0 .oooo -0.0002 0.0000 f0.0002 +0.0005 +0.0005
..
SOTES AND PRECAUTIONS.
Numbers 6, 7 and 8 of Table I show that very large amounts of chromium can be completely precipitated by the barium carbonate method carried out as above described. However, if the amount of chromium exceeds that recommended in the method described herein, i t cannot be readily extracted b y 2 grams of sodium carbonate, particularly if too great a n excess of barium is present. The amount of sodium carbonate used was governed by the directions of Noyes and Bray' who state that, for a successful separation of chromium, not too much sodium nitrate should be present. The separations described herein were made in a volume of 2 5 0 cc., and inasmuch as 2 grams of sodium carbonate were used for fusions, the resulting sodium nitrate concentration was about I . 3 grams per I O O cc. The filtrates were tested for chromium b y removing the excess of lead with sulphuric acid, filtering, concentrating to about I O or 1 5 cc. and making alkaline with sodium hydroxide. No color indicative of chromate was ever obtained, even after adding a little hydrogen peroxide and boiling t o 1 Chrome-vanadium standard: 4 determinations; each gave 1.34 per cent. Average of results of cooperating analysts: per cent. chromium 1.36, per cent. vanadium 0.204. 2 LOC.cit.. Q. 48,Note 4.
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERIhrG C H E M I S T R Y .
Jan., 1912
oxidize any chromium t h a t may have been reduced. Possibly the larger amounts of chromium could have been completely extracted b y one fusion. had more sodium carbonate been used, but the manipulation is then less convenient; moreover, with the usual range of chromium content in commercial steels one need never work with more than 7 or 8 centigrams t o secure a n accurate determination. The boiling with hydrogen peroxide in alkaline solutions before precipitation with lead nitrate is done in order t o destroy any nitrite formed during the fusion. If this were present when the solution is acidified, the resulting nitrous acid would possibly reduce some chromium or vanadium. Five minutes’ boiling will insure destruction of the excess of peroxide if only z or 3 cc. of the usual 3 per cent. solution are used. The hydrogen peroxide should be completely removed before acidifying, inasmuch as it reduces chromic acid.1 The freeing of the: solution from carbon dioxide is an important step, for if this is not done, the precipitate does not settle out rapidly and is not so easy to filter; shaking in a separatory funnel, as described, is a convenient way of accomplishing this. The solutions containing the chromium, after titration, were treated with enough sulphuric acid t o precipitate the lead, which was filtered off and washed with dilute sulphuric acid. The filtrates were evaporated on the hot plate until free from hydrochloric acid and then electrolyzed with a mercury cathode’ until free from iron and chromium. The solution in the electrolyzing apparatus was then tested for vanadium b y hydrogen peroxide, none being found in most cases and in others only traces, showing t h a t the separation under the conditions qiven is practically perfect. It is well t o examine the insoluble from the fusion for chromium by again fusing i t with sodium carbonate and potassium nitrate. The solution from the second fusion is almost invariably colorless when working under the conditions herein recommended. Should there be i i slight yellow color, however, the chromium causing i t can be estimated colorimetrically. A determination of chromium can be made easily in II/, hours. CONCLUSIONS. I . Sources of error in some of the usual methods for determining chromium in chrome or chrome-vanadium steels, which limit the accuracy of the results, are described. 2. The precipitation of chromium from solutions of steels and its separation from practically all the iron can be effected quickly and easily b y boiling with a number of precipitants, herein described. 3. The chromium may be readily extracted from the precipitates b y fusion, and separated from vanadium by precipitating as lead chromate, under the conditions prescribed. BUREAU O F STANDARDS,
.
WASHINGTON.
1
Perchromic acid is fist formed, but is rapidly decomposed.
2
cain. JOG.
ci:.
19
T H E BISMUTHATE METHOD FOR MANGANESE. By D. J.
DELIOREST.
Received October 2 0 , 1911.
There seems to be considerable misapprehension as to the effect which chromium has upon the bismuthate method for manganese. Thus it has been stated that chromium affects the results for manganese b y this method. If, however, the method is properly carried on, the chromium has no influence. I t is true that the bismuthate oxidizes sbme of the chromium to chromic acid, and this is titrated along with the manganese if the manganese is titrated by adding an excess of ferrous sulphate and then titrating the excess with permanganate. ’ This is not the proper way. If the permanganic acid is titrated directly with sodium arsenite until the pink color disappears, the chromic or vanadic acids which may be present do not interfere a t all and the results are accurate. To show this, the vanadium steel standard issued b y the Bureau of Standards was analyzed for manganese with and without the addition of chromium. The Bureau gives 0.669 per cent. as the manganese in the steel. The following results were obtained. Without adding chromium.
With 3 per cent. chromium added as K2CrzOr.
0.666 0.669 0.666 0.666 0.666 0.671 Another steel was run in the same way obtaining: 0.468 0.468
The acid open-hearth steel standard issued by the Bureau of Standards, and for which the Bureau gives 0.407 as their average, and the average b y the CGoperative chemists as 0.412 was analyzed with and without 3 per cent. Cr. The results were 0.403 per cent. Mn without, and 0.405 per cent. Cr with 3 per cent. chromium. Another sample gave 0.489 per cent. without addition of Cr o r V and 0.488 per cent. with the addition of 3 per cent. Cr and I I / ~per cent.
1:. The method as used in this laboratory is as follows: One gram sample is dissolved in 45 cc. of water and 1 5 cc. HNO, (sp. gr. 1.42)and the solution boiled until nitrous fumes are gone. After cooling a little some “bismuthate” is added, a little a t a time, until the resulting permanganic acid or manganese dioxide persists after a few minutes’ boiling. Now KNO, is added to dissolve the MnO, and the solution is boiled a few minutes to expel nitrous fumes. I t is then cooled to t a p water temperature. When cold, bismuthate is added a little a t a time, while the solution is shaken, until about gram has been added. After settling a moment the solution is filtered through asbestos on glass wool (for speed) and the asbestos washed well. Then sodium arsenite is run in from a burette until the pink tinge just disappears. There should not be a brownish color a t the end. If there is, i t indicates insufficient acid. The arsenite is made b y adding t o z I / ~ g. As,Q, in a beaker a hot solution of Na,CO, until the As,O, dissolves. It is then diluted to Z I / ~ liters. DEPARTMENT O F METALLURGY, OHIO STATEUNIVERSITY,
COLUMBUS.
