Jan Ingenhousz (1730-1799). Ingenhousz was born in Breda, Holland. He obtained a degree in medicine from the Catholic University of Louvain in Belgium, summa cum laude, in 1753. From 1768 to 1788 he lived in Vienna as a physician to the Austrian court (Rook 1964; Egerton 2008). He discovered that the ability of plants to purify the air, now known to result from photosynthesis, occurred only when the green parts of plants were exposed to sunlight. He showed that green plants expel oxygen in the presence of sunlight, but under shade or in the dark they produce carbon dioxide.
For three months in 1778 when he was in England, he conducted about 500 experiments the results of which were published the following year (1779). He conducted experiments on air purification following Priestley’s methods and arrived at the same conclusion as Priestley’s that green plants could purify contaminated air. However, he found that it occurred in just hours and not days.
Jan Ingenhousz initially explained his observations applying the Phlogiston Theory (Rook 1964). But in 1796, he adapted the ideas of Lavoisier and others that the gases carbon dioxide and oxygen are involved in air purification and suggested that the carbon dioxide (he called it carbonic acid; Govindjee and Krogmann 2004) in the atmosphere is an important source of carbon for plants. He emphasized that plants do not just engage in the exchange of “good air” and “bad air.” He suggested that consequent to the absorption of carbon dioxide, oxygen is given off while carbon is retained by the plant (Devlin 1975; Hopkins 1999; Moore et al. 2003).
Both Priestley and Jan Ingenhousz, therefore, proved Stephen Hales correct that plants absorb something from the atmosphere. In addition to his finding that sunlight was essential in air purification (photosynthesis), Ingenhousz also investigated various factors affecting this process. These include the differential effects of light intensity, time of the day, types of plants, and parts of plants.
In his work published as Experiments on Vegetables, Discovering Their Great Power of Purifying the Common Air in the Sunshine, and of Injuring it in Shade and at Night (1779), Jan Ingenhousz made the observations below enumerated.
1. Contrary to Priestley’s finding of 6 to 10 days, plants have the ability to correct bad air in a few hours. In correcting bad air, plants produce “dephlogisticated air” (oxygen). They continually produce purified air which mixes with the atmosphere and benefits animal life;
2. This air purification process is subject to the influence of sunlight upon the plant. However, the sun alone has no power to purify the air in the absence of plants, but instead may contaminate it;
3. This operation begins only at sunrise. The rate that this process occurs slows down as the day comes to an end and ceases completely during sunset, with the exception that some plants perform this process somewhat longer than others;
4. The rate that this process occurs is correlated to light intensity or the degree of brightness of the day. Plants shaded by high buildings or heavily shaded by plants do not perform this process but instead produce air (carbon dioxide) that is injurious to animals and even contaminate the surrounding air both during the night and day;
5. The whole plant does not perform this process but only its leaves and the green leafstalks. Fully developed and older leaves produce more “dephlogisticated air” with higher quality than young leaves which have not fully developed;
6. The lower surface of leaves generally expel more “dephlogisticated air”;
7. Plants perform this process regardless of whether they are acrid, ill-scented, poisonous, or otherwise. But some plants produce more dephlogisticated air than others and some aquatic plants perform this process more excellently.
8. Some plants with excellent ability to produce beneficial air in the presence of sunlight surpass others in making the surrounding air noxious in the dark to such a degree that in just a few hours the quality of the air has diminished and that an animal put in it dies within a few minutes;
9. All flowers and, with a few exceptions also roots, make the surrounding air highly noxious both during the day and night;
10. In general fruits, even those which are most delicious like peaches, also render the surrounding air noxious at all times but principally in the dark to such degree that the air can endanger human life if the man is put in a room where a large stock of such fruits is stored.
Note: The lists of contributors and Literature Cited are in the History of Photosynthesis Mainpage. A portion of Jan Ingenhousz’s published results from which the above list was taken is found in Rook A (ed.). 1964. Jan Ingenhousz (1730-99): The process of photosynthesis in green plants is described in a series of experiments. In: The Origins and Growth of Biology. Harmondsworth, Middlesex: Penguin Books, Ltd. p. 215-220.