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.
