MICROCHEMICAL APPARATUS: A LONG-TERM PROJECT' JOHN T. STOCK University of Connecticut, Storrs, Connecticut
N o ONE would pretend that the making of simple chemical apparatus belongs to the higher flights of r e search. However, something on these lines can be done under very difficult conditions, as the writer and colleagues, M. A. Fill and P. Heath, found out in England during and after World War 11. Shortages of materials, time, technical assistance, and even of working space, had to be faced. With the teaching laboratories loaded nearly 12 hours a day, the reduction in accident-risk, atmospheric contamination, and storage requirements following the adoption of small-scale techniques in suitable instances enabled available accommodation to be utilized to the utmost. This led to the institution of a modest long-term project, which still continues on a transatlantic basis, for the design and construction of small-scale apparatus (3). After some years, we were surprised t o receive applications for the manufacture and marketing of some of our devices. This was quite unexpected, since, with few exceptions, we have aimed a t "apparatus that anyone can make." Perhaps this may be illustrated by reference to micro-
(a)
Cliwon tray; ( b ) rniaro watelrbath.
chemical devices for heating, stirring. and a few miscellaneous operations. HEATING DEVICES
A tiny gas flame provides ample heating for many microchemical operations. Direct heating is quite satisfactoryfor brieftreatment such as employed in inorganic qualitative analysis, but when used for prolonged operations such as refluxing or distilling, careful adjustment and ample flameshielding are necessary. One simple form of shielded micro-burner (shown in Fig. 1) consists of an ordinary Bunsen burner from which the flame-tube has been removed and replaced by a small screw-capped reagentbottlewith the bottom cut off (10). The bottle screws into its cap, which is held on the screw thread below the jet by means of a nut made from sheet lead. This can be forced on to the thread without damaging it. Air enters through 6 to 8 holes around the central hole in the cap, when a flame from 5 t o 15 mm. high burns quite steadily under ordinary laboratory conditions. Various attachments may be fitted to this simple device. For example, a snap-on arm will support a micro reaction assembly, while a clip-on wiregauze tray (shown a t (a)) is admirable for drying and warming micro crystallizing tubes, etc. The micro waterbath, (b) made from a small beaker, may also be heated on this tray. A micro test tube or other small vessel may be adequately supported by slipping it within a rubber band stretched between two glass "ears" sealed on the rim of the beaker. Temperature may be reduced by pushing the bath towards a comer of the tray. Similar attachments are applicable to a more robust device which permits a considerable degree of control without altering the flame height (11,19). For less-critical operations a little heater made from a block of wood, two strips of tinplate and a short length of thin brass tubing is useful (IS). Another approach employs indirect heating with a larger fixed-height flame which is relatively insensitive t o draughts and which heats a miniature hotplate (19). The heating effect is controlled by varying the distance between the bottom Presented a t the joint meeting of the New England Association of Chemistry Teachers and the Connecticut Valley Section of the American Chemical Society, Weaver High School, Hartford, Connecticut, April 13, 1957.
JOURNAL OF CHEMICAL EDUCATION
of the vessel to be heated and the surface of the hotplate. Using a soldering iron heating element, the device may he adapted for line operat,ion ( l & , 15). In a form developed as a commercial prototype (Fig. 3, rise and fall of the hotplate is controlled by a knurled thumbwheel. As shown hy Figure 3, proximity control is particularly useful for micro-dist~illat~ioii, etc., of volatile liquids.
Fisvre 2.
Miniature Electric Hstplste
A simple micro blowpipe constructed mainly from a large steel washer and two discs of copper foil has proved useful in the constniction of apparatus from meltingpoint tubes and very thin glass rod. The very small requirement of compressed air is easily supplied by a simple reciprocating device operakd by a filter pump (16). STIRRING DEVICES A feature of the micro-stirrer shown in Figure 4 is the
'"lmpact principle" which ensures self-starting and re-
liable operation (17). Filter-pump surtion applied to the upper side t,uhe causes the mercury, and henre the glass float, to rise in the guide tube. When considerable momentum has been gained, the float strikes the valve rod and drives it upwards thus producing t,he stir-
0
10
20
30
Time, min. ~i~~~~ 3.
Figure 4.
-Hammer-astion" Micro-stirrer
(4 "slave" stirrer.
ring motion and a t t,he same time breaking the varoum by opening the valve. As the moviug parts fall hy gravity, the valve closes and the cycle is repeated ahont, 3 t,imes per second. The stroke of the interchangeable stirrer head may he adjnsted within the approximate limits 1 to 10 mm. This nnit will operate the "slave" stirrer in) through several feet of ruhher tubing connected t,o the lower side arm. The "slave," which is operated by the pressure-waves set up by the pulsati~~g mercury, is merely an easy-fitting glass piston sliding within a glass tubing cylinder and carrying a suitable stirrer head. The "slave" will operate in any position and, by rotating the knob attached to the stop srrem, t,he stroke may he adjusted while running (18). Rotation of the high speed micro-stirrer shown in Figure 5is effected by gentle filter-numn suction. vhen a streak oi air froln the jet impinges on the toothed rotor cut from an ordinary cork (19). At the same time, entry of secondary air hetween the sewing-needle spindle and its glass bearing lifts the spindle assembly slightly, giving almost frictionless running. An allglass form which fits directly into t,he standard taper of a semimicro reaction vessel has also been developed. The availability of cheap, reliable miniature electric motors of lorn current consumption2 renders these at-
assembly
~ i ~ t i ~ of lmhar ~ t iin~- o ~ u i ~ ~ f i tsomimicro -~
No. ISMU3 Distanoe between hotplate aurfsoo and bottom of flask: c w u e 1. 5 in!".. 11. 20 mm., 111,30 mm., I V , 40 mm.
VOLUME 34. NO. 7, JULY, 1957
Figvro 5. High-speed Suction. operated Micro-stirrer (a) Plan view of rotor.
' The Ever Ready
Co., Ltd.,
Holloway, London, N. 7, Eng-
land. Type T.G.18B.
tractive power-sources for micro-stirring. In one form, four la/*inch diameter plastic reagent-bottle caps form a casing for the motor and controlling resistor. A hollow shank allows the unit to be mounted on a ring stand and carries the connecting leads to the battery. Other forms clip on to the neck of the reaction vessel or are equipped with a standard-taper male cone to fit directly into the top of a reflux condenser or other apparatus (20). I n electrometric micro-titration, the mouth of the vessel is often nearly filled by the buret jet, electrode system, etc. A miniature bar stirrer operated from underneath by a rotating magnet is then particularly useful (4, 21). A suitable bar consists of a 5- to 7-n~m. length of sewing needle sealed up in a slightly longer piece of melting-point tubing. For smooth running, the bar should not rotate a t more than about 500 r.p.m. Set a t this rate, however, these small motors will not start reliably. One remedy is to incorporate a booster button to supply an increased starting voltage. A better solution is the use of a motor having a 6 to 1 reduction gear.# This permits the motor to run a t a comparatively high speed and hence to perform reliably. As shown in Figure 6, the small slotted cylinder magnet4 is merely cemented to the face of the larger gear wheel ($8). To prevent a small vessel from "wandering"
"dead-stop end point" titrimetry. In conjunction with a simple directreading titrimeter, the assembly is useful for conductometric titration (4), simple rate studies (6), and for comparing the properties of weak and strong electrolytes (5, 6). A convenient support for conductometric and other microelectrodes is shown in Figure 7. The holder is bent up from a rectangle of sheet brass and has a hardwood stem to permit mounting on a ring stand (7). Stretched over wire
as a thin ri9u.a .I. S"pp0.t COP Micm-eI-rubber band rigidly holds trode systems the electrodes in the notches. Two pairs of notches a fern millimeters apart, as shown, are useful if the electrode-pairs should not touch one another. Apparatus for polarography and amperometric titration is easily made (8, 26); a cell which is very useful for samples less than 1 ml. in volume does however require some skill in glassblowing (9). QUALITATIVE ANALYSIS AND GENERAL
I
I Figure 6.
M i n i a t u r ~Magnotis Bar-type Stirrez
during stirring, it is thrust within a rubber band stretched between brass bolts projecting from the stirrer platform. An alternative form of drive is a filter-pump-operated turbine which has a cork, balsa, or moulded plastic rotor (23, 24). When not causing dificulties such as foaming, loss by volatilization or interference with electrode processes, stirring by means of a stream of fine air bubbles is often very effective. When compressed air supply is not available, a simple electrical (25) or suction-operated (16) pump is useful. ELECTROCHEMICAL DEVICES
Consisting mainly of a length of thin platinum wire sealed into each of two melting-point tubes, a conductometric micro-electrode system may be constructed in about 15 minutes ( 5 ) . If the electrodes are left unplatinized, the assembly is useful for micro-scale Victory Industries, Ltd., Guildford, England. James Neill, Ltd., Sheffield, England; Type M4776A; Radio Shack Corporation, 230 Crown St., New Haven 10, Conn. No. R8128 ABC.
Owing to the favorable surface-to-volume ratio of small volumes of solution, the so-called "pressure" method of saturation with hydrogen sulfide is very effective in semimicro inorganic qualitative analysis (SO, 31). Very little gas is wasted, so that a normallycharged Kipp generator lasts for months and, consequently, the laboratory atmosphere remains uncontaminated. For individual use, a simple pump-action high-pressure generator may be used ( I , 32). A compact unit for semimicro qualitative analysis(27) has been available commercially5 for some years. I t has since been modified to permit the micro-scale "detection of elements" in organic compounds as well (28, 29). This revised form is now in the pilot stage of commercial production. Intended mainly for the identification of organic compounds, a set of small-scale apparatus to our designs (24) went into production in 1951 and has recently been brought up to date? The set packs away into a small uartitioned box, thus permitting easy checking and storage. Features are (i)standardization of neck and stem diameters, so that a single size of pre-bored cork may be used interchangeably, and (ii) use of simple spring clamps for easy assembly and dismantling. A survey made soon after sales commenced showed that, in many cases, t,he sets mere being used for teaching organic preparations in introductory courses. This is not surprising, since it is common British educational practice to include considerable amounts of chemistry, physics, and sometimes biology in all of the final three high-school years. In view of this demand, a version particularly suitable for preparative work has recently Aimer Products, Ltd., 56 Rochester Place, London, N.W.1, England.
JOURNAL OF CHEMICAL EDUCATION
gone into producti~n.~This version incorporates a still-head which permits distillation to follow refluxing by mere interchange of a thermometer and a "coldfinger" condenser (IS). High-efficiency steam-distillation devices are included in both versions; the design in one case is that of E. A. Robinson (0, one of the author's past students. Now available on both sides of the Atlantic' is a compact doublesided unit which was originally designed for demonstrating small-scale organic techniques. It includes assemblies for micro-filtration, simple, fractional, steam, and vacuum distillation, etc., and has since proved valuable in research work and in mobile laboratories. A hand-made prototype (24) was exhibited during the International Congress on Analytical Chemistry, held a t Oxford, England, in 1952. At the invitation of Quickfit and Quartz, Ltd., we collaborated with their Development Department in getting the exhibit into the production form. Our services received an unusual form of acknowledgment, namely, the endowment of the "Quickfit and Quartz" prize a t Norwood Technical College, London. This prize is awarded annually to the best chemistry student of that particular year. As a teacher, i t gives me no little satisfaction to know that our efforts will benefit, in perpetuity, a succession of deserving students. When the unit finally went on the market, it caused quite an interest in the technical press. Someone christened the unit "the vest-pocket laboratory" and the name caught on. The interest spread to the lay press and,eventually, to the BritishBroadcastingCorporation. Before long, a film unit was on site, taking pictures for the television program, "Science Review." The growing interest in the United States is reflected in news reports and in two televised demonstrations. If one lesson has been leaned from this long-term project, it is that there are usually many complicated ways of achieving a purpose. The work really begins when simplification is attempted. The "Micro~d" Semi-micro Organio Set." Grifin and George LM., Alperton, Middlesex, England, The Ealing Corporation, Box 90, Natick, Mass. ' Quickfit and Quartz. Ltd., Stone, Staffs., England, Arthur F. Smith Co ,311 Alexander St., Rochester 4, N. Y.
VOLUME 34. NO. 7 , JULY, 1957
LITERATURE CITED ( 1 ) HEATEI,P., Analyst, 7 9 , 787 (1954). O A., N , School Sn'. Reo., 38,103 (1956). ( 2 ) ~ O B ~ N ~E. ( 3 ) S w c a , J. T., Times (London) Edue. Supplement, No. 2111, 1136 (1955). J. T., Metallurgia, 42,48 (1950). ( 4 ) STOCK, ( 5 ) STOCK,J. T., J. CHEM.EDUC.,31,410 (1954). J. T.,School Science Rev., 31,336 (1950). ( 6 ) STOCK, J. T., Chem. Age (London),71,575 (1954). ( 7 ) STOCK, ( 8 ) STOCK, J . T., Analyst, 71,585 (1946). J. T., Analyst, 71,583 (1946). ( 9 ) STOCK, ( 1 0 ) STOCK,J . T., AND M. A. FILL, Chem. Age (London), 72, 847 (1955). (11) STOCK,J . T., AND M. A. FILL,Chem. Age (London), 71,889 119.U\ - - - .,. ( 1 2 ) STOCK,J. T., AND M. A. FILL, J. CHEM.EDUC.,33, 619 (1956). . . (13) STOCK,J. T . , AND M. A. FILL,J. CHEM.EDUC.,31, 144 (1954). , T . , AND M. A. FILL,Labomtory Practice, 4 , 501 ( 1 4 ) S m c ~ J. (1955). . (15) STOCK,J. T.,and M. A. FILL,Labomto~yPractice, 5 , 344 (1956). J . T., AND M. A. FILL,Analyst, 74,122 (1949). ( 1 6 ) STOCK, J. T., AND M. A. FILL,A m l y ~ t69,212 , (1944). ( 1 7 ) STOCK, ( 1 8 ) STOCK, J. T.I AND M. A. FILL,Analyst, 71,536 (1946). J. T.,AND M. A. FILL,Analyst, 74,318 (1949). ( 1 9 ) STOCK, J. T., AND M. A. FILL,Laboratory Practice, in print. ( 2 0 ) STOCK, ( 2 1 ) STOCK, J. T., AND M. A. FILL,Chem. Age (London), 63, 296 114.5nl - - -- ,. ( 2 2 ) STOCK,J. T., AND M. A. FILL, Mikroehim. Ada, 1, 89 (1953). J. T., AND M. A. FILL,Metallurgia, 41,290 (1950). ( 2 3 ) STOCK, (24) STOCK,J . T . , AND M. A. FILL,J. CHEM.EDUC.,30, 296 (1953). J . T., AND M. A. FILL,Analyst, 74, 52 (1949). ( 2 5 ) STOCK, J. T., AND M. A. FILL,Analyst, 69,178(1944). ( 2 6 ) STOCK, ( 2 7 ) STOCK,J. T., AND M. A. FILL,Chem. Age (London), 67, 85 (1952). ( 2 8 ) STOCK,J. T.,AND M. A. FILL, J. CHEM.EDUC.,33, 345 (1956). J . T.,AND M. A. FILL,School Science Rev., 37, 346 ( 2 9 ) STOCK, (1956). ( 3 0 ) STOCK,J . T., AND P. HEATH, "Small-soale Inorganic Qualitative Analysis," Chemical Publishing Co., New York, 1954. ( 3 1 ) STOCK,J . T., AND P. HEATH,School Science Reu., 36, 193 (1955). (32) STOCK,J. T., AND P. HEATH,Analyst, 7 6 , 496 (1951). \
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