modernmicroscopy : columns : "how to" tutorial series

"How To" Tutorial Series
How to Make/Modify and Use an Alcohol Lamp
by  John Gustav Delly, Scientific Advisor, Hooke College of Applied Sciences, Westmont, IL

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Fuel for the Alcohol Lamp


The two best, and 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&8212;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.


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