September15,1934
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INDUSTRIAL AND ENGINEERING CHEMISTRY
measured by an alcohol-filled thermometer graduated from +50” to -50” C. in degrees. With the bulb of the thermometer in the periphery of the field of a 6X objective and with the asbestos cover in place, readings for the temperature of ice, melting slowly or in equilibrium with water, were consistently 1.5” lower than those recorded with the same thermometer immersed in melting ice to the same extent as when in the cold stage; they were 2’ lower than the freezing point indicated by “cooling curve” data. Undoubtedly a temperature gradient exists between top and bottom of the stage, and horizontal or vertical variations in the position of the thermometer bulb may also affect the temperatures it registers to the extent of one or two degrees. Therefore a specific constant for the stage a t a given temperature should be obtained by comparisons with pure compounds of known melting or transformation point, and with the thermometer in a definite location which should be maintained. The temperature a t different places in the specimen is in reality reasonably free from any horizontal gradient, since freezing may start or progress equally well from any point. POSSIBLE IMPROVEMENTS Based on experience gained from three years’ use of the apparatus described, the following modifications are suggested : The cold stage might well be made thicker to provide a deeper well, so as to decrease the temperature gradient between top and bottom of the cell. The ledges for holding fhe windows should be made deeper; the bottom one so that
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the condenser may be brought nearer the object, the upper one so that objectives of shorter working distance may be used. The stage, as described, cannot be rotated as is d e sired between crossed Nicol prisms or in the measurement of angles. This limitation is removed if pieces of rubber tubing are inserted in the inlet and outlet lines near the stage, lohg enough to allow the stage to be rotated 45” to the left and right. The rubber tubing would also permit the horizontal movement of the stage so that more of the specimen might be explored than is possible by moving the cover-glass in the small free space between the cover-glass and the walls of the well. By cementing the lower window in place, the well could be filled with liquid of low freezing point and immiscible with the specimen. Replacing the air in the well by a liquid would have the advantage of providing quicker and more uniform distribution of heat among stage, specimen, and thermometer. A circulation line of larger capacity, including larger tubing and stopcocks, would provide both quicker extraction of heat from, and lower possible temperatures of, the specimen. The return and feed lines could be shortened by placing the Dewar flask nearer the microscope and the shunt controls on the same side of the microscope as the Dewar flask. LITERATURE CITED
(1) Chamot and Mason, “Handbook of Chemical Microscopy,” Vol. I, pp. 207-8, John Wiley & Sons, N. Y.,1931. (2) Newcomer, Cornell thesis (1928). Unpublished.
R E C ~ I V ZJune D 8. 1934.
Sintered Glass Absorber for Determining Carbon by Wet Combustion P. A. WELLS,0.E. MAY,AND C. E. SENSEMAN, Bureau of Chemistry and Soils, Washington, D. C.
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HE method of Friedemann and Kendall (2) has been used for several years in the Color and Farm Waste Division for the determination of carbon in fermentation solutions, and is suited for this purpose except for the glass bead absorption column. This type of absorber is inherently inefficient, as Friedemann and Kendall have emphasized that a 50 per cent excess of alkali must be present to insure complete absorption of carbon dioxide. Moreover, it has been found difficult to wash the column of glass beads free of alkali, and ordinary glass beads after several weeks of use are so attacked by the alkali that they can no longer be used. Various gas-washing bottles have been studied recently by several workers (3, 4, ?, 8 ) , and the spiral and sintered glass (6)filter-plate types found to be the most efficient. Sintered glass disks of Pyrex glass can be made according to the method described first by Bruce and Bent (1) and more recently by Kirk, Craig, and Rosenfels (6). Thomas (9) found that the latter type of absorber was entirely satisfactory for absorbing carbon dioxide, provided a suitable surface tension depressant was added to the alkali. Butyl alcohol used for this purpose appreciably decreased the size of the bubbles and caused frothing, which was desirable. Using butyl alcohol in a concentration of 0.4 per cent, complete a b s o r p t i o n of carbon dioxide was possible until practically all the alkali was neutralized.
32.5cm
did red
This type of absorber seemed s u i t a b l e for the authors’ purpose because of its simplicity and its efficiency under the widely varying conditions which are possible. Because suitable commercial bubblers werenot available, a number of disks for these absorbers were constructed somewhat after the method of Bruce and Bent ( I ) , the principal variation being that a graphite mold (a type used with satisfaction for several years by the Fertilizer I n v e s t i g a t i o n Laboratory of this bureau) was substituted for the nickel mold. The mold was approximately 5 om. in diameter and 1 cm. thick, machined out centrally to a depth of 3 mm. and a diameter of 2.7 cm. No cover was needed. Ground Pyrex glass of SO-mesh size was tamped into the mold, after which i t was placed in a muffle furnace heated to about 800’ C. and allowed to remain for 2 minutes. The sintered disk can be removed immediately from this type of [mold, and the mold is then ready for further use. The type of absorption tower shown in the illustration was found best suited for the purpose. The indentations are necessary to prevent spray from being carried out of the tube. With a tube of this size and 50 cc. of s o l u t i o n , flows of air up to 100 cc. per minute can be used without danger of mechanical loss. The porosity of the disk, as well as the height and diameter of the tube, can be varied to suit individual needs.
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ANALYTICAL
EDITION
Vol. 6, No. 5
The absorber was tested by the method of Friedemann Typical results with the absorber described, given in and Kendall (2), in which it was substituted for the usual Table I, show that the determination of carbon can be glass bead column. After complete combustion of the sample carried out successfully with complete absorption of carbon (30 minutes’ digestion period) the absorber was raised to dioxide when less than 5 per cent of the alkali remains a convenient height above the bottom of the flask and the unneutralized. This was further evidenced by the fact alkali washed out with hot water free from carbon dioxide. that no precipitate appeared in a trap tube to which barium Usually three washings of 40 cc. each were sufficient. I n hydroxide solution (0.3 N ) had been added and through order to hasten the washing, a hand aspirator connected with which the air was passed after leaving the absorber. a soda-lime tube was used to force the water out of the SUMMARY absorber. The carbonate was then precipitated by adding barium chloride solution, and the stoppered flask was proThe sintered glass absorber described has several adtected with a soda-lime tube while cooling. It has been found vantages over the glass bead absorber previously used for this convenient to use a mechanical stirrer while titrating the determination. It is unnecessary to maintain a large excess excess alkali. To obtain consistent results, carbon dioxide- of alkali and consequently the method has a wider range of free air should be passed over the solution while titrating, application. Washing the alkali from the absorber is easier. particularly when using mechanical agitation, because Difficulties due to the disintegration of the glass beads by the otherwise air is drawn into the flask. Blanks should be run alkali are eliminated. in exactly the same manner as the determination, to correct LITERATURE CITED for carbon dioxide in the apparatus and reagents. (1) Bruce, W. F., and Bent, H. E., J. Am. Chem. SOC.,53, 990 TABLEI. DETERMINATION OF CARBON BY WET COMBUSTION (1931). USINGSINTERED GLASSABSORBER (2) Friedemann, T. E., and Kendall, A. I., J. Biol. Chem., 82, 47 (Butyl alcohol added, 0.5 per cent) CARBON TAKEN SODIUM HYDROXIDE PERCBNTOP O R I ~ I N A L (A0 8ODIUM USaD IN SODIUM HYDROXIDE CARBON OXALATB) ABSORBERo UNNEUTRALIZED FOVND &om Qram 0.1436 0.5 N 4.2 0.1430
4
0.1436 0.1435 0.0722 0.0717 0.0719 0.0278 0.0277 0.0279 60 ml. used.
0.5 N 0.5 N 0.5 N 0.5 N 0.5 N 0.1N 0.1 N 0.1 N
4.2 4.2 51.8 52.2 62.0 7.4 7.6 7.0
0.1430 0.1430 0.0724 0.0718 0.0719 0.0277 0.0275 0.0277
(1929). (3) Friedrichs, F.,Chem. Fubrilc, 4,203 (1931). (4) Halberstadt, S.,IND.ENO.CHEM..Anal. Ed., 4, 425 (1932). (6) Jenaer Glaswerk Schott und Gen., U. 8.Patent 1,620,815(1927). (6) Kirk, P. L., Craig, Roderick, and Rosentels, R. S., IND. ENO. CHEM., Anal. Ed., 6, 164 (1934). (7) Rhodes, F. H., and Rakestraw, D. R., Ibid., 3, 143 (1931). (8) Sieverts, A., and Halberstadt, S., Chem. Fabrilc, 3,201 (1930). . , Ed., 5, 193 (1933). (9) Thomas, M.D.,IND.ENQ.C H ~ MAnal. Rmcairvmn May 18, 1934. The 240th contribution from the Color and Farm Waste Diviaion, Bureau of Chemistry and Soils, U. 6 . Department of Agriculture.
A New Ultraviolet Microscope Illuminator Preliminary Studies of Its Use with Rayons THOMAS HILLDAUGHERTY AND ELMER V. HJORT, University of Pittsburgh, Pittsburgh, Pa.
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HE analytical uses of fluorescence effects due to ultraviolet irradiations have been summarized by Danckwortt (4) and by Radley and Grant (17). Apparatus for both macro and micro observation has been built or suggested by Lehmann (7), Wasicky (24), Reichert ( I @ , Naumann (11), Auer (2)’ Silverman (21),and Singer (23). One or more of the following factors limit the equipment cited above: the expense of quartz lenses, slides, and other acceswries; unsuitability for both macro and micro investigations; lack of flexibility in making the microscope available for other work; lack of suitable ultraviolet intensity; and inability to use the higher powers of the microscope. To eliminate these undesirable features as far as possible, it was decided to make use of an oblique cone of ultraviolet light impinging on the object, securing thereby an even and full illumination with the elimination of shadows, an increased depth of focus causing uneven structures to appear in relief, and the production of as true color values as can be obtained with artificial light. For visible light these results have been obtained with the Silverman illuminator (20, 28), Preston’s top light illuminator (16), and the Leitz ultropaque (8). For fluorescence, the last named has secured these effects using glass equipment. The apparatus described below was designed to secure still further advantages. The apparatus consists of an enclosed annular quartz
mercury arc (Figures 1 and 2). The experimental quartz model of the arc was built to the writers’ specifications by the Hanovia Chemical and Manufacturing Co. This arc operates on line voltages from 110 to 220 direct current, with best results a t about 155 volts, and a lamp bank resistance is used in series, such that the voltage drop across the arc is about 85 volts. From 1 to 2 amperes are required for starting, depending on the voltage. The arc is mounted just above the stage, so that the objective can occupy the position shown in Figures 1 and 2. The mounting is light-proof except for the filters which transmit the ultraviolet rays to the object under examination. It is cooled by fins attached to the arc and by a circulating water system. It is necessary to use a filter to remove as much as possible of the visible light emitted by the mercury arc (4), because its relative intensity obscures the fluorescence. The transmissivity of different filters may cause confusing phenomena. Thus Kogel (6) reported that certain filters transmit red rays which may be mistaken for red fluoresence. The published reports of fluorescence work often fail to specify what filters were used, and in most reports the use of only one filter is mentioned. To avoid the resulting confusion in reportirfg results, data obtained with a number of commercially available filters were recorded. The best results with rayons were obtained by using Heat-
