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PLANT NUTRITION AND PNEUMATIC CHEMISTRY (PMM 189) . First edition, and a particularly handsome copy, of this important work on plant nutrition, experimental physiology, and pneumatic chemistry. "He studied the movement of sap in plants and discovered what is known now as root pressure. He measured the amount of water lost by plants through evaporation and related this to the amount of water present in a given area of soil in which the plants were growing. He estimated rain and dewfall in this connection, measured the rate of growth of shoots and leaves, and investigated the effect of light on plants. He experimented on gases and found that they were obtainable from plants by dry distillation. He was the first to realize that carbon dioxide was supplied to plants by the air and formed a vital part of the plant s food supply" (PMM).Hales initiated a new stage in physiological experimentation with his statical methods, which were characterized by precise quantitative measurements, repetition and the use of controls, and were based on the assumption that that the known laws of matter operated in the bodies of plants and animals as well as in non-living materials. He prefigured the cohesion theory of water movement in plants, although his ideas were not understood at the time, so he did not influence the debate on water transport in plants in the 19th century. He also speculated that plants might use light as a source of energy for growth (i.e., photosynthesis), based on Isaac Newton s suggestion that gross bodies and light might be interconvertible. "In his experiments on plants Hales frequently noticed bubbles of air emerging from the cut stems of vines or rising through the sap, often in such quantity as to produce a froth. This, he remarked, shews the great quantity of air which is drawn in thro the roots and stem. The air, he thought for a time, was perspired off through the leaves; but an inconclusive experiment led him to suspect that the leaves of plants do imbibe elastick air. By 1725 he had performed a few experiments to prove that a considerable quantity of air is inspired by plants. The problem interested him so much that he deferred publication until he could make a more particular enquiry into the nature of a Fluid, the air, which is so absolutely necessary for the support of the life and growth of Animals and Vegetables. These investigations, carried out between 1725 and 1727, were embodied in the long chapter, nearly half the final work, called Analysis of Air. This chapter was to have momentous consequences for the later development of chemistry" (DSB). "While Hales work on the chemistry of air appears primitive by modern standards, its importance was acknowledged by Antoine Lavoisier, the discoverer of oxygen. Hales invention of the pneumatic trough to collect gases over water is also considered a major technical advance. Modified forms of the pneumatic trough were later used by William Brownrigg, Henry Cavendish and Joseph Priestley in their research" (Wikipedia). "Hales s true mentor was Newton, whose last query of the Opticks (1718) was in fact a monograph on the role of attractive and repulsive forces in chemical processes, and whose short Thoughts About the Nature of Acids Hales had also read. He was familiar too with the Chymical Lectures in which John Freind attempted to explain chemical reactions in Newtonian terms" (DSB). Rare in such fine condition. "Stephen Hales (1677 1761) was a dissenting minister, physiologist and chymist who was awarded the Copley medal by the Royal Society in 1739 … In his seminal work, Vegetable Staticks (1727), Hales applied Newtonian experimental method to plant physiology, further developing the chymical queries in the Opticks. The Staticks primarily included analyses to show how great a proportion air is wrought into the composition of animal, vegetable and mineral substances. As Francis Darwin realized, the foundation of Hales views on the nutrition.
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