Mar., 1916
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
method a s described in this paper provided pure gases can he obtained as directed in Bureau of Mines Technicd Paper, 104 ( 1 9 1 5 ) by Burrell, Seibert and Robertson. For accurate work in these determinations larger measuring instruments should be used.
237
volume of the hydrogen peroxide solution and nitric acid in the same manner. The difference between thenumber of cc. of potassium permanganate solution required for t h e blank titration and the number of cc. required for the red lead titration is the amount required for the hydrogen peroxidc 34.2 34.1
A W I D METHOD FOR THE ANALYSIS OF RED LEAD AND ORANGE MINERAL BY
JOXN A. S C ~ Z A ~ F F Z R Received AYPYL4. 1915
34.0 33.9 33.8
In estimating t h e chemical value of red lead and orange mineral, i t is essential t h a t the true red lead, 3 3 . 5 Pb,O,, content or the lead dioxide, PbOl, content be 33.4 determined. Where a large consumption of these 3 3 . 3 products or their purchase on specifications necessitates 33.2 a determination of these constituents a t d l times t h e 33.1 methods in use a t present are rather long and involved. The following method has been perfected for this 32.8 analysis and gives accurate results in a most rapid 3 2 . 7 inn.on manner. The method depends upon t h e initial decomposition 9 9 . 6 9 99.38 of t h e true red lead, PbaO,, with nitric acid, according 99.07 t o t h e following reaction:' 98.77 PbaOd 4HNOa = zPb(NO& H10 HQPbOa. 98.46 The H2Pb03 or PbOa is then decomposed with hydrogen 98.16 peroxide as follows:2 97.85 Pb02 HlOz = PbO H20 On. 97.55 The excess of standard hydrogen peroxide used is then 97.24 titrated with a standard potassium permanganate c 96.94 solution. 96.63 I n carrying out the analysis, one gram of t h e red, 96.32 lead or orange mineral is treated with 1 5 cc. of nitric 96.01 acid, having a specific gravity of 1 . 2 . The mixture 95.71 is then stirred until t h e first reaction given is complete, 95 40 as is evidenced by a n entire disappearance of all red color. There is then added from a calibrated burette or pipette exactly IO cc. of dilute hydrogen peroxide, made u p of a mixture of I part of 3 per cent hydrogen 94.49 peroxide solution t o 3.5 parts of water. It has been 9 4 . 1 8 found t h a t a I O cc. automatic pipette, with a three9 3 , R8 way stop-cock, is excellent for delivering a definite 93.57 volume of hydrogen peroxide solution a t all times. 93.26 After the addition of t h e hydrogen peroxide solu92.96 tion, the resultant mixture is stirred until almost 92.66 complete decomposition of t h e lead peroxide has been 92.35 effected, a s shown by the second reaction. The 92.04 decomposition is completed by t h e addition of a little 9 1 . 7 4 hot water and stirring. The contents of t h e beaker, 91.43 after complete decomposition and solution of t h e lead peroxide, are diluted with hot water t o about 2 5 0 cc. no. I volume and titrated directly with a standard potassium permanganate solution having an iron value of o.oo5. necessary for the complete decomposition of the lead The solution is titrated t o a faint pink permanganate Peroxide. This difference multiplicd hy 3 . o j 8 givcs t h e percentage of red lead according t o the following color. proportion: A blank titration is then made on exactly t h e same aFe : PbrOl = 0.005 : X, or, 1 1 2 : 6 8 j = 0.005 : X I Treadwell and Hall. "Analyfieal Cbemirtry,'' Vol. 11, p. 623. ' [ b i d . . Vol. I. p. 53. whence, X = 3.058.
+
+
+
+
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+
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238
T H E J O U R N A L O F I N D U S T R I A L A N D E L V G I N E E R I ~ V GC H E M I S T R Y
T o determine t h e lead peroxide present t h e difference is multiplied b y 1.067, according t o t h e following proportion: 2Fe : PbOz = 0.005 : X , or, I I Z : 239.0 = 0.005 : X whence, X = 1.067. These calculations have been arranged in a series so devised as t o permit t h e direct reading of t h e red lead percentage. The basis of t h e calculations depends on the fact t h a t each cc. of potassium permanganate solution (iron value, o.ooj) is equivalent t o 3.058 per cent of true red lead; or, each 0 . 1 cc. is equivalent t o 0.3058 per cent true red lead on a one gram sample. A red lead or orange mineral having a I O O per cent true red lead content requires 32.7 cc. potassium permanganate solution of the above strength. The calculation. therefore, arranges itself as follows: Each 0 . 1 cc. on the selected burette represents 0.30j8 per cent true red lead. The number 32.7, being equivalent t o I O O per cent, occupies a n analogous position on the chart. -4 representative portion of t h e series is shown alongside Fig. I . The series is continued upward in steps of 0.1and downward in steps of 0.30 and 0.31 t o such points as are required for t h e red lead usually examined. Fig. I is a n illustration of t h e apparatus in use; calculations have been continued upward t o 40.0, or t o t h a t point where t h e hydrogen peroxide solution used is of such strength t h a t I O cc. of t h e hydrogen peroxide solution require 40 cc. of t h e potassium permanganate solution. Calculations have been continued downward t o 9.48 per cent true red lead content. I n using t h e series the chart is attached t o t h e burette by a screw clamp. A blank determination is first made on t h e hydrogen peroxide solution and the value found is placed opposite zero on t h e burette. I n t h e analysis of t h e red lead t h e value is then read off directly. As a hypothetical case we will use hydrogen peroxide solution with a blank titration of 34.1 cc. I n the analysis of t h e red lead or orange mineral 4.2 cc. of potassium permanganate solution are required for a final titration value. The calculation shows the difference between the two readings t o be 29.9 cc. or multiplied b y 3.0j8 equals a true red lead percentage of 91.43 per cent. Comparing this with t h e series of calculations we find 4 . 2 cc. from the value 34.1 t o be 91.43 per cent. Should i t be preferred t o determine. directly t h e lead peroxide content, t h e calculation will be based on the value 0.1067 for each 0.1cc. on the potassium permanganate burette. I t is understood t h a t t h e division must be made t o correspond with each 0.1 cc. on t h e burette. I t is always advisable t o make several blank determinations each day where this analysis is constantly carried out, or when only occasionally used a blank titration should be made before t h e final analysis. The strength of t h e hydrogen peroxide solution will vary from time t o time when a stock solution is kept on hand, b u t t h e permanence of t h e potassium permanganate solution renders t h e method accurate over a long period of time. CHEMICAL LABORATORY, PICHER LEADCOMPANY JOPLIN, MISSOURI
Vol. 8, No. 3
CHROMIUM OXIDE ANALYSIS By ALLAN J. FIELD
Received August 13, 1915
The chief difficulty in chromium oxide analysis is in t h e fusion. Sodium peroxide affords t h e quickest and most, complete fusion b u t has the disadvantage of attacking nickel, copper and platinum crucibles. ,4s nickel crucibles contain iron they cannot be used if iron is t o be determined in the chromium oxide. The method of heating t h e crucible as suggested b y ’Treadwell-Halll has given very good results. He recommends using a porcelain crucible which is placed inside a larger porcelain crucible and heated for fifteen or twenty minutes over a small flame. The fusion is dissolved out with water and evaporated down t o dryness to remove the last traces of peroxide. The author has found the followingmodificationstoafford decided advantages. Instead of using a porcelain crucible, which interferes with the silica determination, a platinum crucible is used. The sodium peroxide has very little action on the platinum crucible when i t is placed inside of a porcelain crucible and heated with a low flame. After making twenty determinations there was a loss of only 0.019 g. in the weight of t h e platinurn crucible, which loss took place principally in t h e cleaning of the crucible after each determination. Another modification is t h a t i t is not necessary t o evaporate t h e solution t o dryness t o decompose all peroxide as 2 0 minutes’ boiling decomposes it entirely; in fact after I O minutes’ boiling no peroxide could be found. ( T o detect peroxide t h e following test was worked o u t : To 5 cc. of a I per cent solution of sulfanilic acid add one drop of t h e sodium chromate solution, which should be neutral, then 2 drops of a 5 per cent oxalic acid solution. If peroxide is present a pink color develops immediately. This is a very delicate test and will show minute quantities.) For the determination of chromium the following volumetric method has given excellent results: Onehalf g. of t h e finely powdered chromium oxide is mixed intimately with 3 g. of sodium peroxide in a platinum crucible. The crucible is placed inside of a larger porcelain crucible and heated with a low flame so t h a t t h e mixture just melts. After heating in this manner for 2 0 minutes all t h e chromium is converted into soluble sodium chromate. The fusion is dissolved out with water and the solution boiled for 15 or 2 0 minutes. If there is a n y iron it will be insoluble and should be filtered off before proceeding further. The solution is made neutral with hydrochloric acid and diluted t o 2 50 cc. in a graduated flask. An aliquot portion of I O O cc. is taken out into a liter Erlenmeyer flask, I O cc. conc. hydrochloric acid are added and the solution diluted t o about 300 cc. with water. About 3 g. of potassium iodide are added and t h e liberated iodine is titrated with Arjlo sodium thiosulfate. T h e gravimetric determination of chromium as oxide does not give very accurate res6lts probably due, 1
“Analytical Chemistry,” Vol. I1 (1913), 6 7 5 .
