if a continuous shaker is used. Seco?zd, if the conditions of dilution, etc., are those given in the preceding tables no red or yellow compounds are observed in the white tribromphenol precipitate. I n addition to the above experiments, tests were run by the two methods to determine the error which might be introduced in the determinations due t o chemicals, evaporation of bromine due t o the use of ordinary one-half liter bottles, methods of working, etc. Thus, an error might be introduced b y running the hypob. omite solution into the phenol without shaking if the region where the hypobromite was most concentrated became alkaline. Several tests were made to determine this, but no appreciable effect was noticed. A series of six determinations to find the effect of titrating back with the thiosulphate after periods of 1 , 2 and 3 minutes (continuous shaking) from the time when the IC1 was added, gave results which showed a maximum error of o 5 per cent. within themselves. Accordingly a n error of not more than 0.5 per cent. is introduced if the solution is shaken only I minute after adding the potassium iodide. Blank experiments were run under the same conditions as the original determinations which showed that the maximum error introduced by the solutions, manipulation, bottles, etc., was 0.3 per cent. Direclioizs.-( I ) ,\'/IO sodium thiosulphate and a -V/IOof either hypobromite or bromide bromate. 20 per cent. K I and I / : ~ per cent. starch solutions. ( 2 ) Into a joo cc. bottle, fitted with a ground glass stopper, put 60 cc. water, 5 cc. hydfochloric acid (sp. gr. 1.2) and then add 15 cc. of the unknown phenol solution which is t o be determined and which has previously been diluted t o about -Y;Io. If the solution is weaker than L Y / ~ ono previous dilution is required. Add quickly enough X / I O hypobromite or bromidebromate solution to make the solution yellow and then add in addition ' I O per cent. of the amount already added. Place the stopper in the bottle and shake continuously for one minute. Add t o the solution in the bottle 5 cc. potassium iodide solution ( I O per cent.) and again shake for three minutes. Wash down the stopper and sides of the bottle and titrate the solution with the -V/IO thiosulphate, using starch solution as an indicator. The starch must not be added until enough thiosulphate has been run in t o make the solution almost colorless. The quantity of thiosulphate used represents the quantity of free iodine, and therefore the quantity of excess bromine. The difference between this quantity and the known quantity of bromine added gives the amount of solution present. Each cubic centimeter of .V/IO bromine used up is equivalent t o 0 . 0 0 1 5 6 gram of phenol. SUMMARI'.
I . The results show that by the above methods of manipulation, either with the hypobromite . o r with the bromide-bromate solution. phenol determinations can be made within an error of 0 . 3 per cent. with only one minute of continuous shaking after the solution containing the bromine is added, i. e . , the reaction
period may be reduced from 30 minutes to I minute without sacrificing accuracy. 11. The phenol in each case was diluted until it was approximately .Y/IOO before the determination was made. The resulting precipitate with the hypobromite or bromide-bromate solution was white and flocculent in each case and the precipitate showed no traces of red tetrabromphenoquinone or yellow tribromphenol bromide. 111. I n order to secure correct results, the phenol solution must be acid after the bromine is added. If i t is alkaline, a n error is introduced which increases as the concentration of the phenol in the solution diminishes and the reaction period increases. IV. The error introduced by shaking the solution for only one minute after the IC1 solution is added before titrating back with thiosulphate is 0.j per cent. Three minutes shaking eliminates this error and longer shaking has no effect. Y. The bromide-bromate solution has the advantage over the hypobromite of being permanent. When the solution used was first made, its strength was 0.0949,3 After three months duplicate tests The hypobromite solution weakened gave o 09495 one-third per cent. every twenty-four hours for the first few days Lfter the solution was made. The bromide-bromate solution has not the unpleasant odor or free bromine. A\7.
DEPARTMENT OF INDUSTRIAL
RESEARCH,
vUIVERS1TY O F KAPI'SAS.
LAWRENCE
THE COLORIMETRIC DETERMINATION OF IRON IN LEAD AND ITS OXIDES. B y J O H N -4.SCHAEFFER
Received June 20, 1912.
The determination of the small percentage of iron always found in lead and its oxides must frequently be made by chemists working in industries where any appreciable amount of iron in raw materials has a deleterious effect on the finished product. This is especially true in the use of red lead and litharge in the manufacture of high-grade cut glass, and lead and its oxides in the manufacture of lead accumulators, where the determinations are constantly made The gravimetric determination of this constituent necessitates a lengthy and a more or less inaccurate analysis, owing t o the many operations entailed. A volumetric determination is also in many cases not sufficiently accurate and rapid for estimating the very small percentages which are often present. The following colorimetric method was developed to fill this need and i t has been found that no other method compares with i t in rapidity, ease of manipulation, or in accuracy for the estimation of the small percentages of the above constituent present in lead and its oxides. The method is a modification of Thomson'sI method, so adapted as to be readily applied t o the above mentioned analysis. I t is carried out in the following manner: I n the analysis of litharge or metallic lead, treat one gram of the sample in a beaker with 1 5 cc. of water 1
J . Chem. SOC.,1886, 493.
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660
T U E J O U R N A L OF I . Y D U S T k I i 4 L A A Y D EA'GIA\'EERI.YG
and sufficient nitric acid t o convert all the lead present t o lead nitrate. Should there be any separation of basic lead nitrate add more water until complete solution is effected. I n the analysis of red lead, treat one gram of the sample with I O cc. of water and sufficient nitric acid to convert all the oxide present, excepting the lead dioxide, to lead nitrate. Add I O cc. of hydrogen peroxide ( I : 3 . j ) to the solution, and boil for a minute until all the oxides of lead pass into solution. After complete solution of either the metallic lead, litharge or red lead, boil the. nitrate solution gently for several minutes to convert all the iron t o the ferric condition, cool the contents of the beaker, neutralize the free njtric acid present with ammonium hydroxide and render faintly acid with nitric acid. A solution made from red lead may, after neutralization and the subsequent addition of acid, show the presence of lead dioxide. When this occurs, the solution can be rendered clear by the addition of a few drops of the hydrogen peroxide solution. Wash the contents of the beaker into a I O O cc. Nessler cylinder, add 1 5 cc. of dilute ammonium sulphocyanide ( I : 2 0 ) and dilute t o the mark. The ihtensity of the blood-red color depends upon the amount of iron present. The color is compared with a blank made in the following manner:
A solution of ferric ammonium sulphate of known strength is required. This is made by dissolving 0 . 7 0 2 2 gram'of ferrous ammonium sulphate in water. A4cidifywith sulphuric acid, heat to boiling and add a solution of potassium permanganate until all the iron is converted t o the ferric condition. Only the very slightest pink tinge may be present after the addition of the potassium permanganate, as this tinge will fade away, while the presence of a pink color tends to vitiate the results. Allow the solution t o cool and dilute to one liter. One cc. of this solution equals 0.0001gram of iron. Prepare the blank b y pouring into a I O O cc. Nessler cylnder I O cc. of hydrogen peroxide of the above strength, provided hydrogen peroxide was added for the solution of the oxide, approximately the same amount of nitric acid as was required for the solution of the original metallic lead or oxide, and 1 5 cc. of ammonium sulphocyanide solution. Dilute to I O O cc. and titrate to the exact color developed in the sample under examination, b y the addition of the standard ferric ammonium sulphate solution. One cc. of this solution equals 0.01per cent. of iron when a one-gram sample is used. The percentage of iron present should not require more than 2 or 3 cc. of the standard t o equal i t , or the color will be too deep for comparison. '
I t will be found t h a t the color can be accurately compared to within 0.001 per cent. of iron content. The small percentage of copper present in lead and its oxides does not interfere with the reaction. LABORATORY O F PICHER L E A D COMPANY, JOPLIW, M O .
CHE-MISTKZ'.
Sept., 1912
A RAPID MICROSCOPICAL METHOD FOR T H E DETERMINATION OF ARSENIC, AS ORPIMENT, IN SBELLAC.' B Y ROBERTS C H W A R Z . Received July 15, 1912.
As is well known, orpiment, the mineral form of arsenic trisulphid, is very generally added to shellac in India, where this product is collected and prepared for the market. Orpiment .is added merely t o make shellac more opaque and light straw-colored. An attempt has therefore been made t o obtain from India shellac t o which no orpiment has been added, but i t has been found that, for some unknown reason, almost all shipments of so-called "arsenic-free'' goods contain from small amounts to considerable quantities of arsenic, mostly in the form of orpiment. Therefore i t appeared advisable to develop a method of qualitatively determining orpiment in shellac, which method would be more rapid than the Gutzeit or Marsh tests. Such a method has been evolved and bases itself, ( I ) upon the fact that orpiment is insoluble in alcohol and can be precipitated from alcoholic solution of shellac b y centrifugal motion, and ( 2 ) , upon the characteristic appearance of orpiment under the microscope. When examined in this manner, orpiment appears as transparent t o translucent granular masses and imperfect crystals of a distinctly characteristic yellow-greenish color. The method, therefore, is very simple and rapid, as can be seen from the following: A Io-gram average sample is ground fine in a coffee mill and then dissolved in 1 5 cc. of methyl alcohol, solution being hastened b y shaking and warming the flask. The varnish is then poured into a graduated tapering tube and this revolved in a centrifugal machine for 5-6 minutes a t 1000-1500 revolutions per minute. This causes the precipitation of the greater part of the insoluble material, which contains the orpiment. The varnish is then decanted, the precipitate shaken with methyl alcohol and the tube again revolved in the centrifuge for one to two minutes. The alcohol is then decanted as thoroughly as possible, the amount of the precipitate recorded, a n d ' a small portion transferred to a microscopic slide b y means of a capillary tube. This preparation is then carefully examined under the microscope, using a magnification of 450-600 diameters. With an ordinary brewers' shellac or varnish containing a normal amount of insoluble material and above 1 5 0 parts of arsenic per million, several pieces of orpiment will be observed in each field. Some shellacs, however, contain a considerable amount of insoluble material, and so the precipitate becomes larger and the number of pieces of orpiment in each field correspondingly smaller. The method has been used not ,only on the common grades of shellac, but i t has also been tried on so-called "arsenic-free'' shipments and three bleached shellacs. The results of all tests have been embodied in a table in which is given the number of each test, description of the sample, amount of the precipitate, number of pieces of orpiment 1 Paper presented at the S e w York Section of the American Chemical Society, June 7 , 1 9 1 2 .
