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Nature seems to have made it difficult for the chemist to carry out his work of preparing and separating substances which can find a place in his scientific system. On the other hand, the naturally separated units of organisms and their organs are often characterized by special substances so that the chemist's work can easily be based on these biological units.


The apparent simplicity of these processes proved deceptive. The number of chemically definable units increased with accelerated speed from the beginning of the nineteenth century. Toward its end, the very multiplicity which sometimes became confusing made it possible to solve many problems. The genius of the great "natural philosophers" of earlier times had its successors in the genius of chemists who constructed a new unity by fitting together separate pieces of special experience. At first, however, the organismic products had to be taken apart and transferred from a biological system to that of elements and molecules.
In 1827 William Prout (1785- 1850) distinguished between three groups of food materials: fats, proteins, and sugars. From the combustion of sugars which he carried out he concluded that sugars are related to starch and characterized by containing oxygen and hydrogen in the proportions in which these elements are present in water. They are hydrates of carbon, or carbohydrates.
The conversion of starch into the sugar found in grape juice (glucose) was carried out by Gottlieb Sigismund Kirchhoff, a German pharmacist in Russia, in two ways: by heating with dilute sulfuric acid or by digesting with the "gluten" of malt (1811, 1814). ...
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