An Improved Design of Rodgers Ring Burner G. FREDERICK SMITH, University of Illinois, Urbana, 111.
to serve as supports for a triangle of nichrome wire threaded through holes drilled through the wire ends as shown in Figure 1. The modified Rodgers ring burner is shown in Figure 2. The base of the apparatushas been greatly increased in diameter. An iron plate 3 mm. thick is cut 20 cm. in diameter, with the outside edge beveled and with an 80-mm. hole in the center.
T
HE Rodgers ring burner (E. Ha Sargent Co., Catalog N ~ 2372) . has so many features which may be used to
advantage by the analytical chemist that additional attention ought t o be directed to it by describing modifications in design which will extend its field of usefulness. Improvements which have been found by extended use to be very satisfactory are therefore described. The unmodified R o d g e r s burner is shown in Figure 1. The design of base and gas a n d a i r adjustment are a cross between the P. G. and E. type of burner (A. H. T h o m a s Co., Catalog No. 2594) and the Boyce adjustable burner (Central Scientific Co., Catalog No. 11065). The gas intake is adjusted by a needle valve with milledhead disk which moves up and down at the lower end of the vertical tube, serving as mixing chamber as in the Boyce burner, with a bushing type of air-intake adjustment for altering proportions of gas and air burned as in the P. G. and E. type. The Rodgers burner terminates at the upper extremity in a bronze r i n g , 87 mm. outside diameter and 72 mm. i n s i d e diameter and 14 mm. thick, attached to the burner barrel by a hollow U-shaped support 40 mm. deep. There are 12 flame jet openings on the inside of the bronze ring approximately 3 mm. in diameter. Supported by the gas-mixing tube of t h e R o d g e r s burner there is attached an inverted tripod support for three heavy-gage wires, termiFIGURE 1. UNMODIFIED RODG- nating above the ring burner and returning inside the ring ERS BURNER
:num ph "disk, isaattached, , s , using e , small o 's&ews, , ~ to~thewunder ~ side ~ ~of the ~ ~
needle-valve regulator of the unmodified burner and a pointer is fastened to the regular base, as shown in section A-A. The barrel of the burner is calibrated to aid in adjusting the height of the wire crucible support on the burner barrel. The iron-wire crucible supports of the unmodified burner are removed and in their place a 4-mm. nichrome wire bent as shown is substituted. The triangular nichrome-wire crucible support of the original burner is replaced by a platinum wire. A iece of stainless steel 45 mm. in diameter and 41 mm. high is drxled and machined to allow the insertion of a 25 to 35-ml. platinum crucible with a fairly close fit, as shown in Figure 3. The crucible should be left to protrude at the top 3 to 4 mm. This stainless-steel radiator just fits within the nichrome-wire crucible supports with their platinum-wire triangular base.
In use the burner is connected to the gas supply (natural or artificial gas), with the needle valve closed and the supply line valve open. The flame jet magnitude is then controlled by opening the calibrated needle-valve adjustment to the desired position and properly regulating the air mixture employed. A nichrome-wire gauze may be placed over the burner on the upright nichrome supports. A beaker placed over a flame on the wire gauze may be raised or lowered, using the adjusting screw on the calibrated burner barrel. Almost any degree of temperature ordinarily employed may be thus maintained to a very close margin, * 5" or even less. A wash bottle may be kept hot t o the desired degree without boiling. A platinum crucible may be heated from the top downwards by supporting it on the platinum triangle and raising i t e
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A c
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RINGBURNER FIGURE 2. MODIFIEDRODCERS
FIQURE 3. CRUCIBLE
With stainless steel crucible radiator
484
MODIFIEDRODGERS BURNERWITH RADIATOR AND PLATINUM CRUCIBLE
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NOVEMBER 15,1936
ANALYTICAL EDITION
gradually into the surrounding jets of the gas ring burner. The stainless-steel radiator may be inserted as shown in Figure 2 with an even better effect in the volatilization of sulfuric acid from a platinum crucible inserted within the radiator, or i n , the charring of filter paper prior to final ignition a t low heat, and finally a t higher heat, with the radiator removed. Many
485
other applications will occur to the analyst. The enlarged base provides needed stability not given by the unmodified Rodgers burner. The writer believes that the user of the newly formed burner will be well compensated for the effort involved in remodeling. R E C E I V ~August D 25,1936.
Standard Liquids for the Microscopic Determination of Refractive Index A. H. KUNZ AND J. SPULNIK University of Oregon, Eugene, Ore., and Oregon State Agricultural College, Cowallis, Ore.
T
HE refractive index of a material is a definite physical
constant which, when easily determined, is a valuable aid to the rapid identification of many substances. Identification by this method has the advantage of not requiring the consumption of the material under investigation. Microscopic methods for the determination of refractive indices are especially useful and have long been used in the identification of minerals (4), and more recently in the identification of alkaloids and fibers (3). Of the microscopic methods available, the most generally applicable are those comparing the index of refraction of the material with a liquid of known index. In the Becke line method, the crystal or particle is immersed in a liquid of known index of refraction on a microscopic slide and viewed through a microscope with an objective whose numerical aperture is about 0.50. On raising the tube of the microscope, a halo of light around the particle moves from the medium of lower to the medium of higher index of refraction. By substituting other liquids the index of the material is obtained within the limits of the liquids available. In the oblique illumination method the particle is similarly compared with liquids of known index. In this case an objective of low aperture is substituted and light is made to pass obliquely through the drop, either by tilting the mirror to one side or by shading a part of the light source. The crystal is shaded on one side. When using a substage condenser in the system the crystal is shaded on the same side as the shadow in the field if it has a higher index of refraction than the surrounding medium, and on the opposite side if its index is lower (I, I,6, 6). The Becke line method serves best with particles having faces nearly perpendicular to the stage of the microscope; the oblique illumination method for particles whose cross sections are more nearly lenticular. Either device is capable of detecting a refractive index difference of 0.002 to 0.003. However, such small differences are seldom required. Since comparison with liquids of known refractive index is the essence of the determination, a series of liquids whose refractive indices vary by small and regular intervals is required. Chamot and Mason (I) suggest such a list (p. 385). However, such lists contain many natural oils whose indices often are found to be different from the published values, furthermore, the intervals are not regular, varying from 0 to 0.02 in the range of the most frequently used liquids. Such difficulties can be overcome by making artificial mixtures of totally miscible pure liquid compounds, whose refractive indices are far apart but whose vapor pressures are nearly the game (for stability). Not many liquid pairs have this desirable combination of properties, but a search of the literature revealed the fairly common compounds listed in Table I. From Table I i t is evident that the range of refractive index between 1.6582 and 1.4234 can be covered by mixtures of a-bromonaphthalene and heptylic acid and the range between
1.4981 and 1.3841 (or between 1.4234 and 1.3841 if no overlapping with the other series is desired) by mixtures of mesitylene and ethyl propionate. Furthermore, n-butyl phthalate can be substituted for the more expensive heptylic acid above 1.4932. Chemicals of technical grade were employed. An Abbe refractometer was used for the refractive index determinations. For each pair of liquids to be mixed a graph was made relating the percentage by volume of each component and the refractive index of the mixture and from this graph was read the ratio of the components required to give the desired refractive index. The mixtures were made from small burets and the index was checked with the refractometer. If the agreement was not within 0.001 it was easily adjusted by trial and error and checking. TABLEI. REFRACTIVE INDEX AND VAPOR PRESSURE OF ORGANIC LIQUID8
Compound
Vapor Pressure
c.
a-Bromonaphthalene n-Butyl phthalate Heptylic acid Mesitylene Ethyl propionate
110 110
90 20 20
Refractive Index at 20”
1Mn.
3.5 3.8 1.9 27.15 27.75
1.6582 1.4932 1.4234 1.4981 1.3841
By this means a set of liquids from n = 1.655 to n = 1.385 with intervals of 0.005 was prepared. The mixtures were kept in small glass-stoppered bottles. One year after preparation the liquids containing a-bromonaphthalene and butyl phthlate or heptylic acid had remained constant to within IL refractive index of 0.002, even though they had been inadvertently exposed to sunlight for an indefinite period. Under ordinary usage, the liquids containing ethyl propionate and mesitylene remained constant within 0.005 for a period of 3 months. Since the liquid mixtures described above cover the range of refractive index of a large number of minerals and of all the common textile fibers, they are especially useful in these fields. Identification of organic compounds, of course, is limited to those which do not dissolve in the liquids,
Literature Cited (1) Chamot and Mason, “Handbook of Chemical Microscopy,” New York, John Wiley & Sons, 1930. (2) Johannsen, “Manual of Petrographic Methods,” New York, McGraw-Hill Book Co., 1918. (3) Kunz, A. H., and Price, A. C.. Textile World, 84, 1438 (1934). (4) Larsen, E. S.,U. S. Geol. Survey, Bull. 679 (1921). (5) Winchell, N. H. and A. N., “Elements of Optical Mineralogy,” New York, John Wiley & Sons, 1928. RECEIVEDJuly 29, 1936.
