INDUSTRIAL AND ENGINEERING CHEMISTRY
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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
