The ubiquitous alcohol lamp, or spirit lamp, seen being used to heat the contents of the retorts in this delightful engraving from the frontispiece of Worthington Hooker’s First Book in Chemistry for the Use of Schools and Families (Harper & Brothers, New York, 1862), is one of the oldest pieces of laboratory apparatus. The earliest versions, burning oil, and used in conjunction with the blowpipe, were employed by goldsmiths in ancient Egypt for making jewelry.
Alcohol lamps have been present throughout the history of chemistry. There is even one included in virtually every child’s chemistry set, or, if not included, directions are supplied for constructing one. In spite of its long history, most alcohol lamps are not used properly, resulting, most often, in flooding of the fuel, leading to burning corks and other fire hazards, as well as corrosion of the metal parts. Additionally, most commercially available alcohol lamps need to be modified for use in the microscopy laboratory, where, in addition to general heating requirements, the flame needs to be made smaller, in keeping with the scale of microchemical glassware and technique. Amongst the considerations in making and/or modifying an alcohol lamp for microscopical use are:
- size, capacity, and form of the fuel container (faceted/unfaceted, globe-shaped, squat; glass, metal);
- nature of the fuel and its temperature when burned;
- fuels and the visibility of their flames;
- caps: ground-glass, steel, aluminum, brass; glass hood, metal hood;
- wick material: woven cotton, cotton string, glass fiber;
- wick size and shape;
- wick’s feed mechanism;
- wick’s feed-through support: glass, brass, copper, steel, ceramic;
- provision for pressure equalization.
Common Faults with Alcohol Lamps and Their Use
The three most common faults with alcohol lamps and their use in the microscopy laboratory are:
- failure to provide for pressure equalization, and
- use of too large a wick, especially one that is also not kept trimmed.
Of these, the most important is the failure to provide for pressure equalization. In totally sealed systems, such as those illustrated in Figure 1, changes in temperature and atmospheric pressure will cause the alcohol lamp to act like a liquid barometer, forcing the alcohol up and out of the wick; even the heat from the hand will cause the alcohol to be driven out, especially so with an overfilled lamp. Removing the ground-glass stopper and lighting the lamp will ignite the excess alcohol, creating a fire hazard. Well-designed alcohol lamps have a tiny hole drilled through the cap or cork to act as a “breather tube” or vent to maintain equal pressure inside of, and outside of the fuel reservoir.
Overfilling of the lamp with fuel is an easily corrected mistake. If the lamp reservoir is only filled about half way, or somewhat more, there will be less likelihood of sloshing alcohol up the wick, wick support, or out of the pressure equalization vent when handling.
For microscopical use, the wicks, as normally supplied, are much too large. As smaller wicks do not seem to be commercially supplied with these lamps, the average lamp needs to be modified. Inserting a short length of narrow metal tubing with an inside diameter about the size of cotton wrapping string is a common expedient, if not the most pleasing aesthetically; such a modification is shown in the case of the alcohol lamp on the left in Figure 1. Both of the lamps in Figure 1 lack a vent for pressure equalization.
Let’s look at some examples of alcohol lamps, and then comment on them.
Some Examples of Alcohol Lamps
Figure 1 illustrates two alcohol lamps found in a typical industrial laboratory; they are both glass-stoppered, and employ a cork surmounted by a metal disc and wick support–both show evidence of having burned around the cork, following flooding; notice also the buildup of soot in the ground-glass cap on the left, and the general corrosion of the metal parts. Both lack a vent.
Figure 2 illustrates, on the left, an almost new version of the same kind of glass-stoppered alcohol lamps as in Figure 1, but with a cork that fits lower in the neck. On the right of Figure 2 is an example of an alcohol lamp with a threaded neck, and an aluminum screw-threaded cap, with integral wick support, and a loose-fitting aluminum hood. Neither lamp has a vent hole.
Figure 3 illustrates a Balsam bottle that has been converted into an alcohol lamp; the hood, with ground-glass base, is missing—perhaps that is why someone converted this container. The hole in the cork has not been bored straight, and the wick does not protrude enough. There is no vent hole.
On the right, in Figure 3, is illustrated a replacement cap and wick assembly for an alcohol lamp with a threaded neck. It features a captive wick cover, and the wick end has been bound to prevent fraying. This assembly could be improved upon by drilling a 1/16” or smaller hole in the top of the metal screw cap, to act as a pressure vent.
Figure 4 illustrates two examples of faceted fuel reservoirs. The faceted feature is not merely decorative; it is an old design purposely made so as to be able to tip the lamp while it is in use, as illustrated by the lamp on the right. The reason for tilting the lamp while in use is so that when soldering, or using the blowpipe, or when performing borax bead and microcosmic salt tests, or sharpening tungsten needles with molten sodium nitrite, drippings will not fall on to the wick, extinguishing the flame. This style of alcohol lamp is often called a jeweler’s alcohol lamp. The jeweler’s lamp on the left has been fitted with a cork, and modified for micro use. The jeweler’s lamp on the right employs a threaded metal cap and hood. Neither lamp has a vent hole, which would be a marked improvement.
Figure 5 illustrates several designs of wicks and their feed-through supports. The brass feed-through on the left is paired with a woven glass fiber wick; this fitting replaces a cork. The woven-cotton wick on the right has been paired with a formed glass feed-through support, which would have to be fitted through a cork, or used without one. The upper wick assembly uses a combination glass and ceramic wick support, paired with a glass fiber wick. All three of these are intended for contemporary oil-burning lamps used for decorative purposes, with or without optional aromatherapy intentions, but they can be adapted to the laboratory alcohol lamp. A vent hole is not generally necessary when using these wick supports, as they fit loosely in the mouth of the reservoir—another reason to avoid overfilling.
Figure 6 illustrates three alcohol lamps that are components of chemistry sets for youngsters; similar alcohol lamps have been supplied in such kits for over 80 years. The lamps illustrated here are all relatively small—about one ounce capacity—but that size is totally adequate for both these sets and for general microscopy; indeed, similar lamps are often a part of microscope sets for youngsters. The three lamps here are all 40-50 years old. The alcohol lamp on the left, from a Gilbert Chemistry Outfit, is fitted with an arrangement for elementary blowpipe work; the tip is constricted to a narrow opening, and in use a piece of rubber tubing is fitted to the lower end, and the user blows through the other end of the tubing, keeping the cheeks fully puffed out, inhaling through the nose in typical blowpipe fashion, so as to maintain a steady stream of air to produce a very sharp, intensely hot flame. The alcohol lamp in the middle, from a Gilbert Chemistry Outfit of a different era, is typical and unremarkable. The alcohol lamp on the right is from a Chemcraft Chemistry Outfit (Porter Chemical Company), and has the molded-in legend “Porter Alcohol Lamp”; the wick is badly in need of trimming! None of these lamps feature a vent hole.
Figure 7 is a page from a Chemcraft Chemistry Outfit manual, describing and illustrating the use of the blowpipe feature of the alcohol lamp.
Figure 8 is The Alcohol Lamp page from the Skilcraft® Chemlab® Manual. The text says “Do not fill to the top of the bottle” and “Fill the lamp bottle with alcohol only to the start of the neck or lower.” The “Fill Line” in the illustration is, however, too high. This manual also says “The best fuel for the alcohol lamp is any commercially available denatured ethyl alcohol (grain alcohol), available only by prescription…. Do not use methyl alcohol (wood alcohol) because it has additional poisonous properties, isopropyl alcohol is readily available, but it will burn with a sooty flame.”
Figures 9 and 10 are pages from other do-it-yourself sources; interestingly, the text in Figure 10 recommends making a wick cap from a brass rifle cartridge (this reference is from a UNESCO source).
It was Short’s Microscopic Determination of the Ore Minerals, M.N. Short, Geological Survey Bulletin 914, USGPO, Washington, D.C., Second Edition, 1940) who illustrated and described the use of a narrow brass tube and cotton string to make an alcohol lamp for microchemical methods–see Figure 11.
Figure 12 illustrates two British-made alcohol lamps—both are excellent. The capacity of both lamps is about two ounces. They are both dimensionally stable, and both employ ground-glass hoods of different design. The lamp on the left has a loosely laid in ceramic wick holder, and is vented by its loose fit. The lamp on the right has a female-threaded brass fitting cemented to the glass neck, and a threaded screw-in brass top/wick holder, which does have a vent hole drilled through! Filled no more than about halfway, this lamp is ideal for general heating purposes. In Britain, these spirit lamps commonly burn methylated spirit, often slightly tinged with gentian violet, as illustrated in Figure 12.
Figure 13 illustrates an interesting alcohol lamp for portable or field use. It is part of a World War II Field, Needle Sterilization Kit. It is nickel-plated brass, and fit in the bottom of a cigarette-package-size, front-opening metal box with this burner at the bottom, and an elongated, round-bottomed sterilization tray on top, which was just large enough to hold one or two hypodermic needles. One quarter-ounce of alcohol provides enough fuel for this lamp to burn for one hour. This is the alcohol lamp I use in my field kit.
I recently had the opportunity to modify a commercially-available alcohol lamp for one of the staff members, and then two others on the staff also requested one. I started with the purchase of an alcohol lamp from McCrone Microscopes & Accessories; this lamp is illustrated on the left in Figure 14. It is not a bad design—small, stable, metal cap/wick holder and hood made of brass; the only thing it was missing for microscopical work was a pressure-equalization vent, and a smaller wick. A vent was made by drilling a 1/16” hole through the top of the cap. For the smaller wick I decided to custom-make a piece of brass that would fit inside the supplied opening, but that would itself have a much smaller opening that would accept a fine woven-cotton string, or a fine woven glass fiber wick. The custom-made piece is shown lying between the two lamps in Figure 14, and installed in the lamp on the right.
Specifically, the outside diameter of the wick tube was 0.275”, and the inside diameter was just under 0.250”. I started by chucking a 2” length of ¼” diameter brass rod into my Unimat, a small hobbyist’s lathe, and turned a 5/32” length at the end down to 0.16” diameter. This end was then center drilled, and a 3/32” hole was drilled something more than 1” deep. The rod was then turned down to 0.24”. The other end of the rod was then cut-off and faced so that it was 1” long, plus the 5/32” extension; this is the piece shown lying down in Figure 14. This adapter was then epoxied into the wick tube, and the new string wick threaded through. Figure 15 shows a close-up of the completed modification, wick reducer and breather vent. As a final touch for my colleagues, I embellished the shoulder of their personal lamp with their own initials, by employing a rapidly rotating zirconium rod chucked into a hobbyist’s motorized hand tool.
Fuel for the Alcohol Lamp
The two best, least expensive fuels for the alcohol lamps are denatured ethanol (ethyl alcohol; grain alcohol), and methanol (methyl alcohol; wood alcohol; methylated spirit); both can be cheaply obtained at hardware stores or home-improvement centers. I have seen people use absolute ethyl alcohol in their alcohol lamps, but, in addition to being wasteful of high-grade ethanol, the disadvantage I see is that the flame produced with absolute alcohol is non-luminous, so that it is easy to forget that it is burning, and difficult to see the flame’s dimensions. Denatured ethanol, without added dye, seems to me to be more commonly used in North America. In the British Isles, methylated spirit or “meths” is generally used. Methylated spirit has, as its principal component, ethanol >60% (commonly 90%) which is denatured (made unsuitable for drinking) by the addition of methanol <10% (commonly 5%) or methyl isobutyl ketone (<10%); there is also a small quantity of water, together with a trace of bitrex to add unpleasant taste, or pyridine; and a dye is added as a visual indicator that the product is not for drinking—this may be fluorescein or a blue or purple aniline dye. There are hundreds of recipes for denaturing ethanol.
In addition to personalizing one’s own alcohol lamp with their monogram, it is also possible to further individualize one’s alcohol lamp by adding a touch of dye to achieve some characteristic color, and to add a few drops of one’s favorite perfume or cologne to the fuel!
There are differences in the heat of combustion for different alcohols, and there are websites that treat the energy transformations in such chemical combustion reactions, but in practical use of the alcohol lamp they make little material difference.
Extinguishing the Alcohol Flame
If the cap is simply placed over the flame, and left there, yes, the flame will be extinguished; however, as cooling takes place, a vacuum is formed, and fuel will be sucked up the wick, causing flooding. To extinguish the flame properly, the cap is placed over the flame, like a candle snuffer, until the fire is out, then the cap is put aside for a few minutes until the apparatus cools, then the cap is finally replaced to retard fuel evaporation.
There are significant differences in the temperature of various regions of alcohol and candle flames, and different portions are either more oxidizing or more reducing, but these differences are best learned by developing the technique that comes from using the various portions of the flame in borax bead tests, charcoal block fusions, and blowpipe analysis, as well as conducting sublimations, melting point determinations, decompositions, melt-backs, and other thermal microscopy procedures. A good book for learning these procedures as applied to minerals is, Identification and Qualitative Analysis of Minerals by Orsino Smith (Van Nostrand, New Jersey; Second Edition, 1953). The main, immediate improvements that can be made to all alcohol lamps is to provide a small vent hole, and not fill the fuel reservoir more than about half way. Next, reduce the wick size for the required smaller scale of work by improvising or custom-making a diameter-reduction adapter.