January 15, 1935
ANALYTICAL EDITION
and Allport and Skrimshire (1). The reagents and materials were tested to prove the absence of lead and sulfide. The sodium sulfide solution was made as suggested by Francis, Harvey, and Buchan (2). The solution remaining in the electrolytic beaker was poured into the casserole containing the liquids used in washing the anode, and the beaker and cathode were well rinsed. The solution in the casserole was then evaporated to a volume of 10 ml. over a steam bath. Any particles of lead peroxide which might have been present dissolved during the process. In the meanwhile, 2 ml. of 10 per cent potassium cyanide solution, 5 ml. of 6 N ammonium hydroxide, and 2 grams of ammonium acetate were $aced in each of two exactly similar tall 50-ml. Nessler cylinders. he solution in the casserole was neutralized with 6 N ammonium hydroxide and transferred to one of the cylinders. Water to the 50-ml. graduation and 3 drops of sodium sulfide solution were added. Finally, the cylinder was shaken repeatedly until the ammonium acetate was dissolved and the solution was uniform. The other cylinder was treated similarly, except that a known amount of a lead nitrate solution, containing 0.01 mg. of lead per ml., was added instead of the solution from the casserole, After a little ractice, it was easy to determine within 0.05 mg. the number or milligrams of lead present in the unknown solution by noticing the color intensity, and this quantity of lead was added to the standard cylinder for best comparison. The solutions were compared in a Leitz colorimeter. The colorimetric value of the lead left in solution after electrolysis was in error from 5 to 20 per cent, but since this value was a small addition to the value determined electrolytically, the result was a considerable lowering of the total percentage error, which without the colorimetric correction was from 2 to 10 per cent. The method was tested by analyzing measured volumes of a solution of lead nitrate containing 0.5 mg. of lead per ml., prepared by dissolving a weighed amount of pure test lead in nitric acid and diluting with water to the proper volume. Since the method was developed for determining the lead
3
content of solutions containing a small amount of acetic acid (left after several hours’ boiling) a drop of glacial acetic acid was added to the known test solutions. A few of the solutions did not contain acetic acid (indicated in Figure 1) and it is readily seen that the presence of acetic acid in such small quantities did not affect the electrolytic precipitation of lead peroxide. With samples containing from 2.5 to 15 mg. of lead the deposit of lead peroxide adhered strongly t o the anode and did not drop off even under vigorous shaking. The results of the various test analyses are summarized in Table I, and in Figure 1 the absolute error in milligrams of the individual analyses is indicated. The vertical sections of the chart show the total amount of lead in the various test solutions. The accuracy in the most unfavorable cases was about 1.5 per cent, and in the majority of cases it lay well below 1 per cent.
TABLE I. MICRODETERMINATION OF LEADBY ELECTROLYTIC-COLORIMETRIC METHOD LEAD TAKEN
Me
.
15.00 12.50 10.00 9.00 5.00 4.50 4.00 3.50 3.00 2.50
AVERAQE LEAD No. OF FOUND EXPERI- ElectroColoriMENTS lytically metrically 12 2 12 4 1 3 21 2 7 3
haximum
-ERRORMinimum
AN
Average
Me.
Me.
Me.
Mg.
%
14.836 12.210 9.821 8.753 4.884 4.324 3.882 3.353 2.844 2.321
0.13 0.26 0.13 0.24 0.08 0.15 0.12 0.12 0.14 0.15
0.149 0.078 0.090 0.034 0.036 0.043 0.071 0.028 0.043 0.054
0.003 0.017 0.006 0.021
0.29 0.37 0.34 0.24 0.70 0.68 0.72 0.77 0.83 1.2
o:i)i7 0.002 0.026 0.002 0.009
LITERATURE CITED (1) Allport and Skrimshire, Analyst, 57,440 (1932). (2) Francis, Harvey, and Buchan,Ibid., 54,725 (1929). RmcmrvsD November 8, 1934.
Determination of Selenium Quantitative Determination on Animal Matter and Clinical Test in Urine H. C. DUDLEY AND H. G. BYERS, Bureau of Chemistry and Soils, Washington, D. C.
R
OBINSON, Dudley, Williams, and Byers (1) report
procedures for the determination of selenium and arsenic in a variety of materials. These methods were developed in response to the necessities of an investigation of the selenium content of minerals, shales, soils, vegetation, and animal tissues and products. Selenium has been found in the tissues and in the blood, feces, and urine of all animals which have ingested seleniferous food, and also in the milk of selenized cows, whether the cows have been fed seleniferous vegetation or have been given inorganic compounds of selenium. Selenium has also been demonstrated in eggs from selenized hens. The development of an accurate method of determination of selenium in these materials is essential for satisfactory work and a clinical test as an aid to diagnosis of selenium poisoning is urgently required. The procedures detailed in this paper are believed to be an advance upon those previously reported, QUANTITATIVE DETERMINATION IN ANIMALTISSUES AND
PRODUCTS 1. For blood, eggs, flesh, hair, bones, or hoofs, the quantity of material required is from 50 to 100 grams. The material in a suitable state of subdivision is placed in a beaker (400 to 600 cc. capacity), covered with 150 to 200 cc. of
concentrated nitric acid (sp. gr. 1.42), and allowed to stand a t room temperature for from 2 to 3 hours, during which period it is stirred vigorously at intervals. Fifty cubic centimeters of hydrogen peroxide (30 per cent by weight) are added and the mixture is allowed to stand overnight. If frothing occurs on addition of the hydrogen peroxide, foaming over is prevented by vigorous stirring of the foam. The foaming is T;articularly intense with blood, liver, and spleen. After stan ing overnight, the mixture is warmed slowly on the steam bath until frothing ceases, after which 50 cc. more of hydrogen peroxide are added, together with 20 cc. of concentrated sulfuric acid. The mixture is then taken t o essentially complete dryness on the steam bath or hot plate. The cooled black paste is treated with 100 cc. of hydrobromic acid (45 per cent HBr) to which has been added sufficient bromine to make it deep yellow in color. The material is then transferred to a distilling flask and 50 to 76 cc. of distillate are collected. Further procedure is as directed by Robinson et al. 2. For milk, the procedure is essentially as for other animal material, except that a quantity of from 500 to 1000 cc. is advised. The final evaporation should be carried out on a hot plate as soon as the fatty material has separated out as a clear yellow layer on the surface of the mixture. This fatty layer, which also appears with egg yolk and other fatty tissues, makes necessary the use of a hot plate for the complete evaporation. 3. The procedure for urine is similar to that for milk, ex-
INDUSTRIAL AND ENGINEERING CHEMISTRY
4
cept that the sample may be as large as desired. The residual pasty material, if highly colored, may be decolorized by a third treatment with hydrogen peroxide. An example of the application of these procedures is given in Table I, which illustrates the range of values obtained.
TABLEI. SELENIUM CONTENT OF VARIOUS MATERIALS OF ANIMALORWN LIB.
NO.
MATERIAL
SELENIUM CONTENT
P. p . m. B13724 13767 11814 13766 4327 4328 4328 7710 7710 12347 13727 13727 13727 13727 13726 5796 11813 11813 11813
0.02 3.0 0.5 2.0 0.0 0.6 2.0
4.7 1.2 0.0 16.0 27.0 26.0 8.0 5.0 0.1 6.0 1.0 3.0
Vol. 7, No. I
No sample of seleniferous human urine was available, but a normal sample to which was added 0.05 mg. of selenium in 100 cc., as sodium selenite, gave a somewhat doubtful test in 24 hours. A very satisfactory test resulted when 0.1 mg. of selenium was used with 100 cc. of urine, and became clearly defined in 12 hours. A cow which had been selenized furnished urine for the following tests: Ten cubic centimeters of urine containing 0.04 mg. of selenium gave a positive test after standing 12 hours. A 100-cc. sample, containing 0.40 mg., gave a clearly defined positive test in 1 hour. It is unfortunate that no test directly applicable to untreated urine is available. When the attempt is made to apply the foregoing test without treatment with nitric acid and hydrogen peroxide, no satisfactory results were obtained, even by filtering and reprecipitation. LITERATURE CITED (1) Robinson, W. O., Dudley, H. C., Williams, K. T., and Byers, H. GI., IND.ENO.C H ~ MAnal. ., Ed., 6,274 (1934). RECEIVED December 4, 1934.
CLINICAL TESTFOR SELENIUMIN URINE Since selenium always appears in the urine of animals fed with seleniferous vegetation, a clinical test sufficiently accurate for detection of minute quantities and sufficiently simple to be used in a doctor’s office or in a drugstore would be of great benefit as an aid to diagnosis in areas known to be affected by a selenium soil. The procedure outlined is relatively simple and is the best the authors have as yet been able to devise. A quantity of urine ranging between 100 and 500 cc. is placed in a large beaker and treated with 25 cc. of concentrated nitric acid and 30 cc. of hydrogen peroxide (30 per cent by weight). If seleniferous vegetation has been consumed, normally 100 cc. is a
sufficiently large sample. The mixture is slow1 warmed, and if rapid evolution of ases threatens loss the bubbfes are broken by vigorous stirring ofthe foam. After foaming ceases, the mixture is evaporated t o dryness on the steam bath or hot plate. If the residue is darker than a very light yellow, it is treated with 10 cc. of hydrogen peroxide and again evaporated to dryness. The dry residue is treated with 10 cc. of hydrobromic acid (20 t o 25 per cent HBr) which is colored yellow with half a drop of bromine. Without warming, the solution is filtered through an asbestos felt filter into a test tube of colorless glass. To the filtrate is added 0.25 t o 0.5 gram of sodium bisulfite (NaHS03)and it is then gently warmed for 15 minutes, and allowed to stand for from 1t o 3 days. A pink preci itate indicates the presence of selenium. If the coloration is !ut slight, it may be brought into sharper relief by examination in the sunlight by looking vertically into the tube. The time required for the formation of the precipitate is much less if hydroxylamine hydrochloride or hydrazine sulfate is available for reducing the selenium. If any doubt exists as to the source of any color observed, it may be resolved b filtering the material through a fine asbestos filter, washing witK water, and redissolving the pink coloration on the filter in from 3 t o 5 cc. of hydrobromic acid which is rendered yellow by addition of bromine. The filtrate is reprecipitated with from 0.1 t o 0.2 gram of sodium bisulfite (or with hydroxylamine hydrochloride). No pink color will be observed in the absence of selenium.
To test the validity of the method as outlined, 50 cc. of urine from a normal horse, which gave no test for selenium, were treated with 0.05 mg. of selenium as sodium selenate. No visible test was obtained on the first precipitation with sodium sulfite, but- on addition of hydroxylamine hydrochloride & faint coloration appeared after standing 24 hours. Using 0.1 mg., however, the test was, very pronounced, and reprecipitation as described recovered 0.08 mg. Horse urine is very highly colored and probably offers the m k i m u m degree of difficulty in the application of the method.
An Inexpensive Vacuum Regulator C. W. MCCONNELL, Hyvis Oils, Inc., Warren, Pa.
T
HE author’s method of setting up an apparatus for what
might be called a 100-mm. Engler fractionation may be of interest to lubrication engineers. In the line is a glass T, one arm of which A , is a small capillary used as a leak. This T joins the rest of the apparatus to a mercury gage, B. The leak on the T is covered by a piece of rubber or other suitable material mounted on a flexible steel spring, C, which acts as the armature for the small doorbell magnet, D. The bell or switch for the magnet is the mercury gage which is
pierced by two platinum wires, E,E‘. When the apparatus is exhausted to the desired vacuum, stopcock B on the mercury gage is closed, the mercury rises, touches contact E‘, and closes the magnetic circuit. Armature C is pulled down and opens the capillary leak, and the pressure within the apparatus is kept constant t o within at least the accuracy of a mercury manometer. Obviously, gage B is so adjusted that contact E’ just fails to touch the mercury when stopcock F is open. The apparatus is inexpensive-a couple of dry cells, the glass T, some wire, a doorbell, and an alarm clock spring are easily obtainable and leave the cost of the mercury gage the only expense. The Petroleum Research Laboratory a t the Pennsylvania State College is, so far as the author knows, the originator of the apparatus, but he believes that only his laboratory has fully utilized its really remarkable flexibility. R ~ C E I V BSeptember D 24, 1934
