(b. Mézières, France, 6 September 1836; d. Lyons, France, 26 May 1896)
Raulin was a pupil of Pasteur at the Ecole Normale Superieure. where he first began to study the mineral nutrition of plants. He continued this work at the lycees of Brest and Caen, then returned to the Ecole Normale Superieure as assistant director of Pasteur’s laboratory.
Pasteur had grown yeast in a medium containing saccharose, ammonium tartrate, and ashes of yeast, which supplied all the mineral needs of the growing plant. Raulin therefore determined to nourish a plant experimentally with a carefully controlled mixture of specific minerals. He chose to work with the common mold Sterigmatocystis nigra (or Aspergillus niger), which thrives on saccharose. Having ascertained the ideal environment for its growth—a large dish containing. 3 centimeters of water at 35° C., adequately aerated, in a room kept at 70 percent humidity—he set out to establish empirically the combination of mineral nutrients that would produce the best yield, measured in dry weight, in a given period of time.
After a number of attempts, Raulin determined the most efficient mixture of nutrients to be 1,500 grams water, 70 grams saccharose, 4 grams tartaric acid, 4 grams ammonium nitrate, 0.6 gram ammonium phosphate, 0.6 gram potassium carbonate, 0.4 gram magnesium carbonate, 0.25 gram ammonium sulfate, 0.07 gram zinc sulfate, 0.07 gram ferrous sulfate, and 0.07 gram potassium silicate. This mixture is now called Raulin’s medium, or Raulin’s fluid.
The chief value of Raulin’s experiment lay in his establishment, by trial-and-error methods, of the importance of each of the nutrients in his mixture, especially the minerals. For example, he eliminated potassium from the mixture, and the weight of the yield dropped from 24.4 grams to 0.92 gram; he was therefore able to demonstrate that the presence of potassium in the medium resulted in a yield of 26.6 times greater weight—or. in other terms, that the specific utility of potassium was 87, since 0.271 gram of potassium increased the yield by 23.48 grams. Raulin studied each element in the same way, and found that nitrogen produced 153 times the yield, phosphorus 182, magnesium 91, sulfur II, iron approximately 2, and zinc approximately 2.4.
In adding a few milligrams of iron and zinc to the medium, Raulin introduced the problem of trace elements. The purity of the chemical products that he used was at best doubtful, and there was no way for him to analyze how much iron or zinc might be contained in the four grams of ammonium nitrate or tartaric acid that he added to the medium. He was nonetheless able to isolate zinc as a trace element; its role in plant nutrition had not previously been recognized.
Raulin published the results of his experiments as “Etudes chimiques sur la vegetation,” for which he received the doctorat es sciences. Pasteur himself was enthusiastic about Raulin’s work, and in 1868 wrote to him that his researches had opened completely new horizons in plant research. In 1876 Raulin was appointed professor of chemistry at the Faculte des Sciences of Lyons, of which he later became dean. He also established a school of industrial chemistry, made a number of agronomic maps, and published a large number of works on a variety of subjects, of which the greatest part concern the production of silk.
Raulin s chief work is “Etudes chimiques sur la vegetation,” in Annales des sciences naturelles, botanique, 5th ser., 51 (1870), 93–299; it was separately published as Etudes chimiques sur la vegetation (Paris, 1905).
J. B. Carles