Supplement to Minutes of the course of chemical instruction in the Medical Department of the University of Pennsylvania / by Robert Hare, printed for the use of his pupils.

  • Hare, Robert, 1781-1858.
Date:
1824
Catalogue details

Licence: Public Domain Mark

Credit: Supplement to Minutes of the course of chemical instruction in the Medical Department of the University of Pennsylvania / by Robert Hare, printed for the use of his pupils. Source: Wellcome Collection.

Provider: This material has been provided by the National Library of Medicine (U.S.), through the Medical Heritage Library. The original may be consulted at the National Library of Medicine (U.S.)

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    In short, as, in the analysis of the mineral kingdom, we de- signate, as elementary, those substances which we cannot ana- lyse further; so, in examining organic products, those sub- stances which cannot be simplified, without destroying their most important characteristics, are to be viewed, as the elementary principles, by which the nature of compounds is to be understood and described. By the distillation of vegetable substances, they are easily resolved into their ultimate elements. These, I have said, are, for the most part, hydrogen, oxygen, and carbon. Some few vegetables, exhibit nitrogen as a constituent. The alka- lies, and some of the earths, or their elements, besides still more minute portions of other matter, are also generally found in vegetables. But, hydrogen, oxygen, and carbon, are, in quantity and importance, greatly predominant. It is a marked distinction, between inorganic, and or- ganic products generally, that the one cannot, like the other, be reproduced by art. This incompetency in chemical skill, has caused the results of chemical analysis to be questioned. Rousseau, having heard Rouelle lecture on farinaceous matter, said he would not confide in any analysis of it, till corroborated by its re- production from the alleged elements. Those, who have any acquaintance with modern chemistry, will not be so skeptical. When diamond and charcoal, are burned under difierent bell glasses, in difierent portions of the same oxygen gas, and, in lieu of them, carbonic acid gas is found, in each vessel—who would hesitate to admit both sub- stances to consist of carbon, because this element cannot be recovered in its crystalline form ? I pointed out, early in my course, the very great discord- ancy of the habitudes of carbon, hydrogen, and nitrogen, with caloric—that, while the two latter cannot be obtained, per se uncombined with that cause of the repulsive, or the aeriform state, charcoal can only, by the most intense galvanic ignition, be united with it, to a sufficient degree to become aeriform.