1780
ANALYTICAL CHEMISTRY
The "open area" angle on the C slider (Figure 3) and H slider (Figure 4) is obtained as follows: The optimum weight of carbon dioxide obtained may be considered to be 5 to 20 mg. (1 to 4 ratio), while o timum of weight of water is 2.5 to 10 mg. (also 1 to 4ratio). ?%erefore, the angle will be = es = 180 loglo(4/1) = 108.4' for both the C and H sliders. The positions of the indicator arrows are computed as follows: Each milligram of hydrogen in the compound produces about ,9 mg. of water. Therefore, OH = 180 log,, (2.5/9) = -100.2 , the angle between the broken line of the H interval indica:or and the H arrow. Similarly, ec = 180 loglo5/(44/12) = 24.0 . The form of the nitrogen indicator (Figure 5) is calculated as follows: At 25" C. (approximately room temperature) and 1atmosphere pressure, 1 ml. of nitrog:n weighs 1.1457 mg. Therefore, Ob = 180 log,, (1.1457) = 10.6 . A 0.5-ml. selector (dotted line) is also included; its angle (@) is calculated in the same manner. Since 0.5 ml. of nitrogen a t 1-atmosphere pressure and 25" weighs 0.5729 mg., PV5= 180 loglo (0.5729) = -43.8".
indicate the optimum range of Sam le weight in milligrams. For the few cases in which there is no cLar area, the optimum sample range is indicated by the doubly covered (green) part of the scale. As there will be two green areas, choose the one most distant from the index position of the scale, For Dumas Nitrogen Determinations. If 1 ml. of nitrogen is desired, set the arrow to the theoretical per cent nitrogen on the inner scale and read the sample weight indicated by the A' ( 1 ml.) line on the outer scale. If 0.5 ml. of nitrogen is preferred, use theN(0.5ml.)Iine.
For the analyst who prefers other volumes of nitrogen, other indicating lines can be constructed in an analogous manner. Alternatively, the slider can be divided into segments that will show the sample weight range for any desired volume range. CONSTRUCTION OF RULE
The scales and sliders were computed by use of the e values as described under Theory. A small arrow or "index position" indicated the starting point of the outer scale. Actual construetion of a workable rule consisted of pasting the carbon-hydrogen scale (Figure 1 ) on one side of a piece of stiff cardboard and the nitrogen scale (Figure 2) on the other. The three sliders were traced onto stiff plastic and scaled up to the same size as the scalesofFigures l a n d 2 Thus, the length of the arrows was made equal to the radius of the inner circle of the scales. The length
. Figure 5. Kitrogen Slider Scale up to same size as Figure 1
For Multiplying any two numbers (outer C and H scale and solid lines extending to indicator tabs are used). To multiply ;M X N , set the solid line of the C indicator on M and the solid H indicator line on the index point of the scale. The indicator lines thus form an angle. Without disturbing the angle, move both sliders together so that the H indicator line falls on :V. Read the answer under the C indicator line. The decimal point is set as usual in slide rule calculations. For Dividing (use outer scale and solid C and H indicator lipes). To divide M by N , set the C indicator line on iM and the H indicator line on N . Move both sliders together until the H indicator line rests on the index position. The answer is indicated under the C indicator; fix the decimal point by an approximate calculation. Multiple Operations. The slide rule can be used to perform operations of the type
M XN X 0X P Q X R X S
Figure 4.
Hydrogen Slider
Soale up to same size as Figure 1
of the solid and broken lines and, hence, the radius of the outer circle of the slider was made equal to the radius of the outermost circle of the scales. The indicated area on the carbon slider was colored yellow by masking the uncolored area and then spraying the exposed portion with transparent waterproof ink from an air brush. Similarly, the indicated portion of the hydrogen slider was colored blue. The width of the colored band was sufficient to cover the outermost series of numbers, No coloring was used on the nitrogen slider. Holes were punched with a cork borer in the exact center of the scales and sliders. The apparatus was assembled with a loose-fitting rivet with the sliders face up on the appropriate side of the scales; the carbon indicator placed under the hydrogen indicator. USE OF RULE
For Carbon and H drogen Determinations. Point the C arrow a t the theoreticayper cent carbon and the H arrow a t the theoretical per cent hydrogen (inner scale). The clear area between the yellow and the blue fields on the outer scale will then
by combining the multiplying and dividing steps described above. Reciprocals. The reciprocal of any number may be conveniently obtained by using the Dumas nitrogen scales and the solid line of the indicator. To perform the operation 1/-41, set the indicator to M on the inner scale and read the answer under the same hairline on the outer scale. Fix the decimal point by an approximate calculation. ACBNOWLEDGM ENT
The authors wish to extend their appreciation to William L. Braun, Jr., and Alexander J. Tatun for assisting in the construction of the working models. Grinders for Mulling Infrared Microsamples. Jesse S. .4rd, Eastern Regional Research Laboratory, Philadelphia 18, Pa. VIBRATION
grinder of exceptional simplicity was developed ( 1 )
A for mulling a series of irreplaceable microsamples, and has proved satisfactory over several years of service. Mulling on a
micro basis with this apparatus has been so convenient that the method has replaced all others for crystalline substances in the author's work, even when an abundant sample is available. Microsamples may also be ground with a reversed drill. Mulls may be prepared with a mortar and pestle ( 5 ) , by mashing between the cell WindOWE (S),and by rotating cones (6); and methods developed for tissue mincing (IO)are readily adaptable
V O L U M E 25, NO. 11, NOVEMBER 1 9 5 3 to this purpose. Many substances are soft enough to be mulled on a cell window with a toothpick. Cotton, representative of particul a r ] ~ difficult . substances, was reported to give a suitable mull piepnration after grinding in a vibratory ball mill, and this was regarded as more effective in this special case than the use of ultrasonic energy or a Waring Blendor (4). As an alternative to mulling, one may use films deposited by vacuum sublimation ( 9 ) or from solvents selected for favorable depositing characteristics ( 6 ) . Samples admixed with potassium bromide (8, 9) or polyethylene ( 7 ) may be compressed into appropriate sections. VIBRATION APPARATUS AND METHOD
The apparatus, Figure 1, consists of a commercial holder to vil)r:ite small tools, and a specially constructed hammer and anvil. 5
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1781 without spattering. After a trial, the ear readily recognizes the intensity of the hum associated with a favorable amplitude. With the usual mulling oils, this amplitude could var over a wide range, but it may need restricting to a low level wit1 special media of low viscosity. I n use, a drop of mulling oil is put near the center of the anvil, and the microsample is shaken into the oil. It is important that the sample be n e t by the medium; otherwise the particles would be scattered by the vibrations. The vibrating hammer is passed over the mixture repeatedly. Beneath the head, the action during each stroke is hammering, shearing, sucking, and expelling; and from 30 seconds to 2 minutes are usually sufficient to mull the mixture into a translucent and creamy consistency. Prolonged or excessively violent action may darken the preparation by emulsifying some steel, but probably metals in this state would give only a generalized absorption without specific band structure. LVhen completed, the mull is transferred to the cell windows by scraping and dabbing motions, with the power off when touching the windows. During this step, the flat scraping edges of the hammer are utilized to concentrate the sample into a heap near the point of the anvil. To clean, the grinding surfaces are wiped with absorbent paper and rinsed with acetone, and residues on the hammer are readily loosened by rinsing with the power on. METHOD USING REVERSED DRILL
.4s the vibration grinder was satisfactory, it was not necessary to develop alternatives fully. Therefore, the following method had not had estensive usage, but in tests it seemed satisfactory.
I I
A hole is drilled partly through a metal block, and the sample and oil are mulled together in this hole by the same drill rotating in the direction opposite to its cutting direction. At a properly chosen speed, the spiral slots of the drill continuously force the sample downward to the bottom of the hole, where it is concentrated, and mulling proceeds simultaneously as centrifugal force moves the mixture in a cycle against the shearing interfaces. If the drill is reversed again, and then gently and slowly revolved by the fingers in i b cutting direction as i t is withdrawn, the finished mull may be recovered as two neatly concentrated heaps just C 60 'l~ within the slots near the drill tip. Some laboratory stirrers have .. . m .; .: g .. f : I been adapted from kitchen mixers of the intermeshing twin-blade a t e, and many of these have a separate socket for turning a c%ck in the counterclockwise direction as required for this purFigure 1. Apparatus for Mulling pose. Microsamples
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Holder for vibrating tools. a chuck: b . on-andoff switch; c, one type of ampjitude adjustment B. Hammer d rectangular head; e, shaft to fit into chuck, a' of holder C. Anvil. grinding plate, brazed t o base f A.
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In selecting a tool holder, important considerations are a chuck, a convenient on-and-off switch, and an adjustment for selecting the proper amplitude of vibrations. Lightweight holders, weighing about 0.5 pound and intended chiefly for light marking purposes, are suitable for mulling the microquantities discussed here. These should be distinguished from heavier holders (exceeding a pound), which are awkward with the small hammer described, and are more appropriate with a hammer five or ten times as large. Satisfactory types of holders for vibrating tools are available from laboratory supply, hardware, and handicraft stores. These usually are powered by 50- to 60-cycle, 115volt, alternating current, and function by the simple action of an alternating magnetic field. [Known sources of the lightweight holders are: Ideal Industries, Tnc., 1006 Park Ave., Sycamore, Ill. (Ideal electric marker); and the Burgess Battery Co., 180 No1 th Wabash Ave., Chicago, 111. (Vibro-Graver). ] The anvil has a top of polished stainless steel. This is flat with edges converging t o a rounded point, so t h a t the finished preparations can readily be scraped to a heap on the projecting point for the transfer. This plate is mounted on a f p e bracket, which makes a rigid base heavy enough to resist t e vibrations. The metal junctions both here and on the hammer are brazed with silver solder. The hammer head is a small flat piece with rectangular edges adapted for scraping, and brazed to it a t an angle of about 45" is a shaft that fits into the chuck of the vibrating holder. The bottom portion is stainless steel, and the upper shaft is a section of brass welding rod. The grinder is made ready for use by inserting the shaft in the chuck and adjusting the vibrations so as to give adequate grinding
DISCUSSION
The outstanding previous method for mulling microquantities consisted in grinding the sample with oil directly between the cell windows (3). When this is accomplished skillfully, the economy of sample and the spectral results have unquestionably been satisfactory. It is rather difficult, however, to control the spreading, thickness, and pattern of distribution consistently while grinding the sample sufficiently, and the variable results have sometimes made it expedient to tolerate poor preparations and a low quality of spectra. Unless the sample is ground previously, this method would not be applicable to hard samples, but fortunately most organic chemicals are sufficiently soft. Even with soft samples, however, the windows are scratched by contacts between themselves and may need frequent resurfacing. The vibratory method has the uniform and intensive action characteristic of mechanical methods, and is thought to be far more versatile, convenient, and dependable. It decreases the waste caused by excessive spreading and unsatisfactory spectra, and it grinds harder substances. An outstanding difficulty in micromulling has been regathering the sample for continuing the action and for transferring, but with the vibration technique the grinding is done on flat surfaces, where simple scraping actions are effective for concentrating the sample. The hammer described is of sufficient size to grind 2- to 25mg. samples incorporated in a single drop of oil. Usually a drop of oil weighing from 12 t o 25 mg. is shaken from a delivery tip 2 mm. in outside diameter, and the sample is then visually proportioned to this to give a creamy consistency when mulled. If the ingredients for the mull need weighing, the anvil plate can be made detachable and tared to make this easier. Larger samples can be handled, but they would spread and require an inconvenient number of grinding passes. On the other hand, smaller samplee
A N A L Y T I C A L CHEMISTRY
1782
are readily ground; and the method can be adapted to very small quantities such as those appropriate for manipulations under low-power microscopes. This possibility is of interest in criminology and for electron and x-ray diffraction work. For infrared mulls, the sample is ground in an appropriate oil that does not need removal, but if an oil-free sample is desired, the oil may be flooded off with a volatile selective solvent like hexane. Preliminary results suggest that this procedure may be useful in the preparation of samples for the potassium bromide wafer method (8, 9); however, the usual advantages from grinding in an oil medium seemed to be decreaed with substances like potassium bromide and sodium chloride that fracture into cubes, probably because the surface of the cubical crystals is relatively low.
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LITERATURE CITED
(1) ilrd, J. S., Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, 1951, ANAL.CHEM.,23, 680 (1951)
(Abstract). (2) Blout, E. R., and Fields, hi., J . Am. Chem. SOC.,72, 479 (1950). (3) DuBois, E., Ed., Better AnaEysis, 4 (No. l), 6 (1953). (4) Forriati, F. H., Stone, W. K., Rowen, J. W., and Appel, W. D., Bur. Standards J . Research, 45, 109 (1950). (5) Garlock, E. A., Jr., and Grove, D. C., J . A m . Pharm. Assoc., Sci. Ed., 37, 409 (1948). (6) Randall, H. &I., Fowler, R. G., Fuson, N., and Dangl, J. R.. “Infrared Determination of Organic Structures,” pp. 92-5, New York, D. Van Nostrand Co., 1949. (7) Sands, J. D., and Turner, G. S., ANAL.CHEhr., 24, 791 (1952). (8) Schiedt, U., 2. Naturfonsch., 8b, 66 (1953). (9) Schiedt, C . . and Reinwein, H., Ibid., 7b, 270 (1952). (10) Cmbreit, IT-. W., Burris, R. H., and Stauffer, J. F., “Llanometric Techniques and Tissue Metabolism,” pp. 114, 126, 136-8, Minneapolis, Alinn., Burgess Publishing Co., 1949. PRESESTED in part before the Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, March 5 t o 7, 1961. Mention of names is intended for convenience and must not be construed am a n endorsement or recommendation by the United States Department of Agriculture over others not mentioned.
Device for Rapid Measurement of Chromatographic Rb Values. Anthony J. Glazko and Wesley A. Dill, Research Laboratories, Parke, Davis and Co., Detroit, Mich. for measuring chromatographic Rb A values, which hasdivider been used in this laboratory for more than PROPORTIONAL
3 years, appears to offer certainadvantagesover similar devices recently described in the literature [Rockland, L. B., and Dunn, hf. S., Science, 111, 332-3 (1950); Nettleton, R. hl., and Mefferd, R. B., ANAL.CHEM.,24,1687 (1952)]. As the scale is longer than the paper strip itself, the accuracy of measurement is as good as that obtained by manual measurements with a ruler, and the R, values are read off directly from the end of the pointer. No difficulty is experienced with proper orientation of the paper strip, since the device is transparent and can be laid down directly over the paper strip, holding it firmly in place. This device was first described by the authors a t aSymposiumon Chromatographyconducted by the Division of Medicinal Chemistry of the AMERICAK CHEMICAL SOCIETY in Chicago, September 1950. The device shown consists of a transparent triangular sheet of plastic material, such as ‘/le-inch Lucite or Plexiglas. An R, scale is inscribed on the hypotenuse, and a series of.lines parallel to the scaleisinscribed about 1inch apart on the rest of the triangle. One end of a movable arm having an index line drawn down the middle is attached to the angle opposite the Rb scale with a metal pivot. All lines can be inscribed with a sharp knife or razor blade, and filled with India ink, colored crayon, or enamel to render them easily visible. Approximate dimensions are 18 X 18 X 24 inches. The movable arm is 0.5 X 18 inches. I n use the scale is placed over the paper strip and oriented so that the paper strip is parallel to the scale, with the starting point of the chromatogram on the left-hand leg of the triangle and
the limit of solvent travel on the right-hand leg. The movable arm is then shifted to intersect the spot on the paper strip whose location is being measured, and the Ra value is read directly from the scale. This proportional divider is based on the principal of similar triangles, and has proved to be the most rapid and practical means of Rb measurement used to date.
Simple Method for DBerentiating between Borosilicate and Soft Glass. AI, I
