Roulette Comparator for Colorimetric Analysis JOHNH. YOE AND THOMAS B. CRUMPLER,University of Virginia, University, Va.
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HE roulette comparator is designed to assist in securing a precise matching of colored solutions in Nessler tubes. A revolving circular rack carries a series of ten standard solutions in 100-mI. Nessler tubes. Beside this is a stationary rack which holds the tube containjng the unknown solution. A rachet device on the circular rack allows the standard tubes to be brought, one by one, into a fixed position beside the tube containing the solution to be matched. Below the tube containing the unknown and the standard tube in fixed position beside i t is an adjustable light-reflector, having a mirror on one side and white glass on the
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CROSSSECTION OF OPTICALSYSTEM
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opposite half of the image of the left-hand tube. The observation tube is provided with an eyepiece, E, having a hole 1.5 mm. in diameter and at, the end next to the mirror box is a diaphragm having an aperture 24 mm. in diameter. By having the apertures of the eyepiece and diaphragm properly proportioned, only the image of the bottoms of the Nessler tubes can be seen, thus preventing interference by light reflect,ed from the inner sides of the tubes. A magnifying lens D is placed in the light path between the mirrors and the eyepiece. This enlarges t8hecircular image and permits a better matching of the two half-fields. Upon looking through the eyepiece, the observer sees a large circular field, divided by an almost imperceptible line when the light from the two solutions has the same intensity. The mirror box and observation tube are painted dull black inside. Two metal spring clips whose position is indicated by C w e placed in the mirror compartment, between the mirrors and the lens, to permit the use of color filters. The mirror box is so attached that it can be rotated through 180" to permit a check on the adjustment of the mirrors and on the matching, and also to allow observations in case fumes from the solutions are objectionable. The Nessler tubes (100-ml. low form) have double-plane, fused-on bottoms instead of being ground on the outside only as were the old type bottoms. This is a decided improvement, since a uniform field of the same degree of color intensity is obtained.
reverse side. The white glass is ground to a pIane, matte surface. The source of light may be either skylight (preferabIy north sky) or a daylight colorimeter lamp. The white glass reflector is generally used for matching lightly colored solutions where a low intensity is desired and the mirror for darkly colored solutions where the light intensity must be greater.
A further use of the apparatus is possibIe in case it is desired to compare the spectra of two solutions. The eyepiece, E, is threaded so that it can be removed, and b y means of a fairly short focus lens an image of the two halffields can be formed on the slit (placed horizontally) of a spectroscope. This arrangement also permits photographing the two spectra side b y side on one film.
Light from the reflector passes up through the two tubes under comparison, impinges on mirrors A and B, and is reflected horizontal1 through the observation tube. One-half of the circular fie& of light from the right-hand Nessler tube is cut off by mirror B, the edge of which thus serves as a dividing line between the two halves of the circular field. The image of one-half of the right-hand tube is then observed in juxtaposition to the
The authors wish to express their thanks to the American Instrument Company, Washington, D. C., for building t h e roulette comparator.
ACKNOWLEDGMENT
R E C ~ I V EDecember D 6, 1934.
Determination of the Phosphorus Fractions in Blood Serum R. R. ROEPKE,Kansas Agricultural Experiment Station, Manhattan, Kans.
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N OVERCOMING the difficulty of proper pH control in
determining phosphorus by the co~orimetric method, Green (1) ashed the sample with calcium acetate and finally neutralized with ammonium hydroxide using phenolphthalein as indicator before developing the color, a procedure which does not give satisfactory This procedure has the disadvantage also that the ash contains some carbon particles even with careful heating. The following procedure eIiminates these difficulties: TOTAL PHOSPHORUS. Into a 150-CC.beaker, pipet an aliquot of diluted serum containing from 0.05 to 0.15 mg. of phos horus. Add 2 cc. of magnesium nitrate (50 per cent solution of Mg&O+-
6H20) and evaporate on hot plate, increasing the heat until a portion of the ash has become white. Fifteen to twenty minutes a t the highest temperature are sufficient. If a portion of the ash has become charred, it will be necessary to add several cubic centimeters of water and a drop of nitric acid and repeat the heating. When dry, heat the sample over a free flame (or in a muffle) until all the magnesium nitrate has been decomposed. This should leave a white ash. Dissolve the ash in 2.5 cc. of 10 A ' sulfuric acid and 10 to 20 cc. of water, heating to insure complete solution. Cool, add a piece of Congo red test paper, and neutralize with ammonium hydroxide. Transfer the solution to a 100-cc. volumetric flask through a small funnel containing a bead
or some other form of constriction which will retain the test paper. Add sufficient water to bring the volume to 70 or 80 cc. Prepare standard by adding 5 to 15 cc. of standard phosphorus solution (0.01 mg. of phosphorus per cc.) and 5 cc. of 5Nammonium sdfate to a 100-cc. volumetric flask and dilute to 70 to 80 cc. To both add from a buret 2 CC. of molybdic sulfuric acid reagent (DenigBs reagent). Dilute to the mark, add 0.5 cc. of the stannous &loride solution, and mix. After 1 or 2 minutes in a color.meter, setting the standard at 30. The unknown should read within 3 or 4 units of the standard. Transfer 10 to 20 cc. of the alcoholLIPOIDPHOSPHORUS. ether filtrate (corresponding to 0.2 to 0.4 cc. of serum) t o a beaker containing 1 cc. of magnesium nitrate and proceed as for total phosphorus. TOTAL ACID-SOLUBLE PHOSPHORUS. Transfer 5 to 10 cc. of trichloroacetic acid filtrate (1 volume of serum to 4 volumes of 10 per cent trichloroacetic acid) and 1 cc. of magnesium nitrate to a beaker and proceed as for total phosphorus. Care should be taken to see that all the trichloroacetic acid has been volatilized by heating on the hot plate before heating over a free flame, since too rapid heating will cause it to char. LITERATURECITED (1) Green,H. H., J. Agr. Sci., 18,372 (1928). R E C ~ I W D12, 1934. Contribution No. 183, Department of Chemistry, Kansas Agricultural Experiment Station.
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