BRINTON ON THE DETERMINATION OF MANGANESE. obtained with resistance glass flasks. The percentages of evaporation, varnish and insoluble are given. Oil B Flask (a) Evaporation .... 19.00 Varnish.. .. . .. . 0.18 Insoluble.. . . . 0.28
.
Oil Flask. Evaporation.. . Varnish., . . . . . Insoluble., .
...
.
C (C
)
13.05 0.38 1.88
B (b)
19.03 0.74 0.48 C (d ) 15.77 0.43 1.81
B (C)
19.95 0.75 0.40 D (a) 23.93 1.01 2.30
B
C
(d) 15.08 0.25 0.29
(a)
C (b’)
17.15 0.37 1.90
25.75 1.14 2.29
D
D (d 1 19.32 1.25 2.50
D (b‘) 22.83 0.57 1.89
(C)
13.42 1.27 2.25
Flask (b’), first used for oil C and subsequently for D, replaced ( b ) in which B was heated. It is curious t h a t for one oil it gave high, and for the other low results. I n our opinion, the formation of “asphalt,” or, as we have called it, “insoluble,” is due t o partial oxidation of the oil rather than to polymerization or t o concentration of the asphalt as the oil evaporates. As mentioned above, there was practically no formation of insoluble when the oil was heated to 200’ for three hours in stoppered bottles. When heated for the same length of time in flasks, loosely covered with watch-glasses., there was opportunity for atmospheric oxygen to enter as rapidly as i t was absorbed b y the oil. A t the same time the lack of perfect freedom of diffusion allowed the escape of only the more volatile constituents so t h a t the change in weight was negligible. No varnish was formed, b u t the following percentages of insoluble were obtained 0.47, 0.52, 0.38 and 0.33. Not enough (of this oil was available for a test in the apparatus finally adopted. Although the figures obtained b y heating duplicate samples of the same oil side b y side are often less concordant than could be desired yet, on the whole, the method seems t o be capable of yielding data of value, this in spite of differences caused by unequal heating, variations in the rate of interdiffusion of oil vapors and air and, apparently, obscure catalytic phenomena influenced by the nature of the material in which the oil is heated. At present the method can be used t o compare a limited number of oils with one another. To make i t of perfectly general application would require a standard apparatus of carefully specified dimensions and material. The petroleum ether used would also need to be of very definite composition. Observing these and other obvious precautions, the requirements of the case would be more than met, for in actual practice the conditions must vary considerably more than in a laboratory experiment. It is not claimed b y any one who has worked along this line t h a t the method does more than indicate what may be expected to happen when an oil is in actual use, but even a slight indication is of greater value than complete ignorance, and a laboratory test is more rational than placing implicit confidence in a dealer’s statements. It is our intention t o go more fully into the question of standardization and also t o study the effect of the
237
addition of fatty oils and other substances t o the mineral oils before heating. BUREAUO F STANDARDS. February 22, 1911.
THE DETERMINATION OF MANGANESE BY THE SODIUM BISMUTHATE METHOD.’ By PAULH. M.-P. BRINTON. Received December 24, 1910.
I n looking over the tables of analyses furnished b y the Bureau of Standards at Washington with its analyzed samples of steel, I noticed t h a t the figures for manganese obtained b y those chemists who used the sodium bismuthate method were in nearly all cases a little lower than the general averages obtained b y all other methods. The differences were small, generally from 0 . 0 2 per cent. to 0.03 per cent., b u t as I had noticed the same thing in using the bismuthate method myself, I had a curiosity t o learn the cause of this tendency of the process. I have made a little series of analyses and experiments, the results of which may be of some interest, especially to those who have not yet adopted the method in regular work. As is well known, the method depends upon the oxidation of manganese t o permanganic acid b y adding solid sodium bismuthate to the cold nitric acid solution of the sample. The excess of the bismuthate is filtered off on asbestos, a measured excess of ferrous ammonium sulphate solution added t o the filtrate and the latter then titrated back with potassium permanganate. The method was originated b y Schneider,’ who used bismuth tetroxide, and subsequently developed b y Reddrop and Ramage,3 and b y Brearley and Ibbot8011.4 Blair5 states t h a t the sodium bismuthate method is not only remarkable in its simplicity and ease of manipulation, b u t t h a t for samples containing not over 2 per cent. manganese i t is the most accurate process known. The purpose of my work was to check up Blair’s results (and those of the earlier workers also) and to confirm, if I could, his statement as t o the accuracy of the method. My analyses were made on various samples of the Bureau of Standards steels. I think we may take the averages given out by the Bureau, coming as they do from a variety of independent sources, as figures which represent the highest attainable accuracy in practical work. The methods and solutions were used, in the analysis of the steels, just as they are given b y Blair. I n the ferrous ammonium sulphate solution half the sulphuric acid was replaced by phosphoric acid, as suggested b y Dr. C. B. Dudley. The end point is rendered a little sharper b y this modification as the color due t o the iron is less intense. The solution of manganous sulphate for standardizing the permanganate was carefully analyzed, Read at the Minneapolis meeting of the American Chemical Soaety. Dingl. Polytech.. 269, 224. a J . Chem. S o c . . 67, 268; see also H.Ramage, Chem. News, 84, 209. 4 Chem. News, 82,269; 84, 247. J . A m . Chem. Soc., 26, 793; also “Cltent. Anal. of Iron,” 7th Ed., 121, cf s e a 1
2
238
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 H E E R I N 6 C B E M I S T R Y .
the manganese being determined in weighed portions of the solution both as sulphate and as pyrophosphate. The results by these two methods were concordant. The permanganate was standardized against the manganous sulphate solution, and also against pure Sorensen sodium oxalate, as well as against the “Sibley” standard iron ore issued b y the Bureau of Standards. I n standardizing against the ore, the iron was reduced with amalgamated zinc in a Jones reductor. The titer obtained by the sodium oxalate was identical with that by: the standard ore. Five of the standard steels were analyzed, the last one being a vanadium steel. Table ‘ I shows a comparison between the results obtained b y taking the strength of the permanganate as determined b y the manganous sulphate method, and b y taking i t as determined by sodium oxalate or by the “Sibley” ore. I n these determinations the theoretical conversion factors were used: Na,C,O, to Mn 0.16024, and Fe t o Mn 0.1967. TABLEI.
--
Per cent. manganese. c
Bureau of Standards averages Found with MnSO, as primary standard.. Found with Na2C204 or with iron ore as primary standard
. .. .. . . . . . {
{
0.412 0.410 0.411 0.397 0.398
0.916 0.922
0.920 0.892 0.890
0.760 0.757 0.758 0.732 0.733
0.568 0.557 0.562 0.539 0,544
-
0.669 0.663 0.665 0.642 0.644
From these figures i t is seen that the results come somewhat low if the permanganate is standardized against sodium oxalate or against an iron compound, and the theoretical conversion factor used. It is interesting to note t h a t the results in this table obtained b y the latter method agree very closely with those obtained b y the analysts who used the sodium bismuthate method in the analyses published b y the Bureau of Standards with these samples. (The vanadium steel is a n exception.) The results obtained b y standardizing the permanganate against the manganous sulphate solution are highly satisfactory, and a great many determinations which I have made in addition to those given in the table have convinced me that the degree of accuracy there shown can be regularly attained ; and the process is so simple t h a t no unusual manipulative dexterity is required t o insure correct analyses. I n fact i t is hard to go wrong with the’methods, after the correct titer for the permanganate is once obtained. While standardizing against a weighed quantity of manganous suphate solution is the most accurate method known for the purpose here desired, it is also the most tedious. It requires a gravimetric determination of the manganese in the solution, and upon this result depends the accuracy of the whole process. A slight error made a t this point introduces serious discrepancies in the final results. The simplest method of standardizing is against pure sodium oxalate; but since the figure obtained in this way brings the results too low we must use an empirical factor. The ratio SNa,C,O, : aMn calls for the figure 0.16024, b u t t o obtain correct results I find t h a t the factor 0.1656 must be applied.
April, 1 9 i i
Since permanganic acid has a certain tendency to decompose in dilute nitric acid solution, particularly in the presence o€ much ferric nitrate, it was deemed advisable to investigate the rate of decomposition. Referring to the solution after the excess of bismuthate has been filtered off and when it is ready t o receive the ferrous ammonium sulphate and be titrated back with permanganate, Blair1 says: “ A t a temperature of 5OC. the solution will remain unaltered for several hours, but a t 40’ C. fifteen minutes will show a n appreciable change.” The temperature of a laboratory is never so low as s o , nor so high as 40°, so t o see what danger from this decomposition would be if artificial cooling were not resorted to, I made the following series of determinations on t h e ’ 0.760 per cent. manganese steel from the Bureau of Standards. The temperature of room and solutions was z I ’C. TABLE11. 1
Found. Per cent. Mn. Run strictly according to Blair. The filtration took about 4 minutes, and the ferrous ammonium sulphate was , , , . 0.760 added and excess titrated immediately., . *Process same as before, except that after filtering, an interval of 12 minutes was allowed before adding ferrous ammonium sulphate and titrating.. . , . , . , . [ 0.758 Same, but an interval of 25 minutes was allowed. , 0.755 Same, but an interval of 55 minutes was allowed.. . : 0.750 Same, with an interval of 1 hour and 30 minutes.. . . . 0,740
. .. . . .. . .
2
3
4 5
6: [ 1
. . ... .. . . . . . .. . . . . ... . . . ..
From these figures it appears t h a t a delay of ten or fifteen minutes is practically without effect under ordinary conditions. Twenty-five minutes causes a slight lowering of the results, and a longer time than this has a decidedly unfavorable influence. I t may be mentioned in passing that a large excess of bismuthate is inadvisable, since i t not only increases the cost of the process, b u t also tends to clog the filter rapidly so t h a t fewer filtrations can be made on the same asbestos felt. Just enough bismuthate should be used so that a slight excess is plainly visible in the bottom of the flask or beaker. As regards the application of the method to iron ores low in manganese, I find the method advised by Blair, i. e., treatment of the sample with I O cc. water, 4 cc. H,SO, and 10-20 cc. H F in a platinum dish or crucible, somewhat tedious; and t h a t i t requires so large a n amount of platinum if many samples are to be run is a further disadvantage. I prefer t o dissolve the ore, about I gram, in 1 2 cc. of concentrated hydrochloric acid in a 4-oz. Erlenmeyer flask, evaporate almost t o pastiness, and then add 4 cc. of concentrated sulphuric acid. By boiling down to heavy fumes over a free flame, manipulating the flask in a holder, the hydrochloric acid is so completely expelled that no test for chlorides can be obtained with silver nitrate. The residue is then taken u p with 50 cc. of nitric acid, sp. gr. 1.135;and finished as usual. The process is quite rapid and the results very accurate. A few ores will not yield all their manganese to this treatment, so if the residue appears dark after taking up with nitric acid, i t should be filtered off,fused with a very small amount of potassium bisulphate and added t o the main por1LOC.
cit.
PATRICK A N D W A L K E R O N T E S T I N G GALVANIZED IRON. tion. It should be noted t h a t this same treatment bf the residue may be necessary with some ores even when using the hydrofluoric method of attack. The fact t h a t the method as above given does not eliminate the silica is not really a drawback, since the silica is obtained in a form which does not seem t o clog the filter much. Attacking the ore b y fusing with sodium peroxide was also tried and i t proved fairly successful. Were i t possible t o procure iron crucibles free from manganese this would be the ideal method. Since that seems t o be impossible a t present, I had t o use nickel crucibles. It should be noted that some nickelcontains traces of manganese, but not, I believe, as a rule. I n using this method, I gram of ore is fused with about six grams of sodium peroxide a t as low a heat as possible. A minute or two in liquid fusion is all t h a t is necessary. The crucible and contents are treated with water in a covered beaker, and when the action is over the crucible is removed and one-third the volume of concentrated nitric acid added. The solution is boiled until all hydrogen peroxide is decomposed and everything dissolved but some manganese dioxide which has been precipitated. Ferrous sulphate is added until the manganese is reduced, the lower oxides of nitrogen are boiled off, and the analysis is finished as usual. The crucible is considerably attacked, but if the heat is kept low a dozen fusions may be made in a crucible before it is unfitted for further use. The color, due to the nickel, tends t o obscure the end point with permanganate somewhat, but after a little practice the point can be readily seen.
[CONTRIBUTION FROM T H E
239
RESEARCH LABORATORY OF MASS INST OF TECH1
A P P L I E D CHEMISTRY.
METHOD FOR TESTING GALVANIZED IRON TO REPLACE THE PREECE TEST. By
WALTER
A.
PATRICK A N D W I L L I A M
H.
WALKER.
Received February 27. 1911.
Some time ago one of us1 published a paper on the testing of galvanized and other zinc-coated iron, in which i t was shown t h a t the so-called Preece Test was unsatisfactory from many points of view, although no alternative method was shown t o be equally available. This study has been continued, and it: is now believed t h a t a satisfactory substitute can be given. The Preece Test consists in placing the piece of galvanized iron t o be tested, in a solution of copper sulphate under standard conditions, and observing the number of one-minute immersions which can be made before copper in a bright adherent form will plate out on the article. The accuracy of the test depends upon the following assumptions: first, t h a t the zinc will pass into solution and be replaced b y copper a t a definite rate, and hence the time taken t o dissolve a galvanized coating will measure its thickness; second, t h a t the galvanized coating is homogeneous and t h a t the speed of the reaction between the coating and copper sulphate is constant, that is, the rate of solution is uniform; third, t h a t when the iron base is reachedithe copper will plate out on the iron in a bright adherent film, in contradistinction to the black spongy form in which i t appears upon the zinc coating, and t h a t no bright copRer will be seen until the iron base is thus uncovered.
SUMMARY.
S T R U C T U R E O F Z I N C COATING.
Corroboration of Blair’s statement t h a t for small amounts of manganese the bismuthate is the most accurate method known. 2. When the potassium permanganate is standardized against sodium oxalate or iron, and the titer theoretically calculated, the results come out too low. A gravimetrically standardized manganous sulphate solution is the correct primary standard, but as this method is more inconvenient than the sodium oxalate method, i t is suggested t h a t pure Sorensen sodium oxalate be used, and t h a t the empirical factor 0.1656, and rzot the theoretical factor 0.16024, be used in the conversion of the sodium oxalate figure t o t h a t for manganese. 3. The decomposition of ores by the hydrochloric and sulphuric acids method is suggested as being fully as accurate, more rapid and perhaps more convenient than the hydrofluoric and sulphuric acids method. Fusing the ore with sodium peroxide is recommended as a method suitable for refractory ores.
The correctness of the first two assumptions depends upon a homogeneous structure of the galvanized coating. Although a detailed description of the structure of the different forms of zinc-protected iron now on the market will form the subject of a later paper, we will point out a t this time t h a t this structure is such as would almost certainly preclude the possibility of the Preece Test being a valid one, The coating of a n ordinary hot dipped sheet or wire is made u p of three well defined parts, namely, the iron base or foundation upon which the coating rests, then a layer of a n iron-zinc alloy, and next t o this the layer of zinc. The thickness of the alloy depends upon the temperature of the galvanizing bath, the length of time the iron is in contact with the molten zinc, and upon the flux which is used. I n a previous paper, one of usz stated that this layer of alloy was electro-negative t o the iron. This was a n error introduced b y the use of measurements of absolute potential, and which we herewith desire t o correct. The alloy is much less electro-positive than zinc, but is not electro-negative. Since the rapidity with which the zinc or zinc alloy will pass into solution, and a n equivalent weight of copper be precipitated in its place, is a function of the difference of potential between the two metals, i t will be
I.
UNIVERSITY OF
MINNESOTA.
1 2
Walker, Proc. A m SOC.Testzng Materaals, 9, 431. LOC.cd., p. 432.
