This article appeared in the
"Editor's File"
in The Textbook Letter, Volume 12, Number 3.
Prentice Hall's picture shows an experimental setup in which a candle-holder, a burning candle, a flower pot, and a small plant have been enclosed in a covered glass jar. The jar evidently has no bottom, but it seems to be standing upon a separate, circular base which is made of glass and which evidently engages the lower rim of the jar to form an air-tight seal. If this interpretation of the picture is correct, an experimenter could have created the setup by first placing the candle-holder and the flower pot on the glass base and then installing the jar. (He couldn't have introduced the candle-holder or the flower pot into the jar through the jar's neck, because the neck is too narrow.)
In the accompanying caption, Prentice Hall's writers lead students to believe that the setup shown in the picture was devised by Joseph Priestley (1733-1804), and that "When [Priestley] placed both a plant and a candle in a covered jar, the candle kept burning."
The entire illustration is a fiction. Both the picture and the caption are fantasies, for Joseph Priestley's writings don't contain any record of an experiment in which a plant sustained a candle flame. Moreover, a puny plant like the one shown in Prentice Hall's picture could never have generated oxygen rapidly enough to keep a candle burning.
We can infer how those fantasies originated. Prentice Hall's writers evidently heard that Priestley had done something which involved a plant and a candle and photosynthetic oxygen, so they invented the fake "fact" that he had put a plant and a candle into a jar and had found that the candle burned indefinitely. Then a Prentice Hall illustrator faked a picture to affirm that nonsense.
Though Prentice Hall's pseudohistorical stuff about Priestley is rubbish, Priestley did indeed perform a signal experiment with a plant and a candle. He burned a candle in a closed vessel of air until the air could no longer support combustion; then he put a living sprig of mint into the container and found that, after a few days, the air in the vessel could again enable a candle to burn for a short time. This was one of several important observations, reported by Priestley and by others, that led to the recognition of oxygen as an element and to an understanding of oxygen's role in combustion.
After I saw Prentice Hall's stuff, I wondered: Would a small plant, in a setup like the one shown in Prentice Hall's picture, exert any effect at all on the longevity of a candle flame? To seek an answer I created an imitation of Prentice Hall's setup by using a plastic drinking-water bottle whose nominal capacity was five gallons, and whose shape was much like that of Prentice Hall's jar. I removed the bottle's bottom, and I made a base for the bottle by stacking three layers of terry cloth. When I saturated this base with water and then installed the bottomless bottle, the wet cloth formed a seal with the bottle's lower rim.
I used my bottle-and-base apparatus to conduct trials with a common dinner-table candle and two potted plants that I had got from a garden-supply store. One of the plants was Salvia officinalis, a species of sage; my specimen was about 8 inches tall. The other plant was Vinca rosea, the rosy periwinkle; again, my specimen was about 8 inches tall.
I ran my trials outdoors, in strong sunlight, between the hours of 1200 and 1300, on two successive summer days.
During five trials in which the candle burned alone in the bottle, without any plant, the mean lifetime of the candle flame was 226 seconds. (I considered the flame's lifetime to be the period which began when I installed the bottle on its base, and which ended when the guttering candle suddenly emitted a plume of light-colored smoke.)
During five trials in which the bottle contained the candle and the periwinkle, the mean lifetime of the candle flame was 195 seconds.
During five trials with the candle and the sage, the mean lifetime of the candle flame was 198 seconds.
During five trials with the candle and both of the plants, the mean lifetime of the candle flame was 173 seconds.
I am certain that if Joseph Priestley ever had tried the experiment which the Prentice Hall fakers have attributed to him, he would have seen the same result that I have observed: The presence of a potted plant causes a small reduction in the length of the period during which the air in a closed jar can keep a candle burning.
What induces this effect? The answer, I believe, lies in the fact that the potted plant occupies some space that otherwise would be occupied by air. If a jar contains both a candle and a potted plant, the amount of air that the jar can hold is slightly less than the amount it can hold when only the candle is present -- and since the jar holds slightly less air, the lifetime of the candle flame is slightly shortened.
I thank The Textbook League's research correspondent, Howard P. Lyon, for directing my attention to Prentice Hall's fake stuff about Joseph Priestley. Readers of The Textbook Letter can learn about other follies and frauds that appear in the Prentice Hall Science Explorer textbooks by consulting these two items: "Pandering" in TTL, Vol. 10, No. 5; and "Prentice Hall Concocts a Fake Article and Ascribes It to The New York Times" in TTL, Vol. 11,. No. 3.
William J. Bennetta is a professional editor, a fellow of the California Academy of Sciences, the president of The Textbook League, and the editor of The Textbook Letter. He writes often about the propagation of quackery, false "science" and false "history" in schoolbooks.
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