The organic constituents of plants and vegetable substances and their chemical analysis / by G.C. Wittstein ; authorised translation from the German original, enlarged with numerous additions, by Baron Ferd. von Mueller.

Date:
1878
Catalogue details

Licence: Public Domain Mark

Credit: The organic constituents of plants and vegetable substances and their chemical analysis / by G.C. Wittstein ; authorised translation from the German original, enlarged with numerous additions, by Baron Ferd. von Mueller. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    paratively few cases, be executed satisfactorily, and a qualitative result has mostly to satisfy the operator. 4. To fathom the chemical constitution of a mineral, one or a few grams weight are almost always quite sufficient. On the contraiy, to ascertain qualitatively, and even supei- ficially, all the constituents of a plant, at least a hundred times more material is required, but which, if a profound study of the single constituents is aimed at, has still to be increased ten or even a hundred fold. 5. It belongs to the rarest cases, generally only occurring after intervals of years, to meet, in the analysis of a mineral, with a constituent previously quite unknown, the discovery of which means at the same time that of a new element. In a phyto-chemic analysis, on the other hand, it is not un- common to obtain constituents unknown before. It therefore offers still a very fertile field for discoveries, though it ought not to be overlooked, that the accurate decision in regard to the correctness of such a discovery is mostly no easy task, because it depends on the purity and quantity of the material, which is not always so obtainable. 6. During the analysis of minerals a decomposition of the con- stituents, as regards their elements, need of course not be appre- hended] the occurring changes consist only in the absorption or liberation of oxygen, sulphur, a few other elements—and volatile acids; the relations of these to the object of examination, whether they are constituents of the same or not, are already answered satisfactorily by other operations of the analysis. The phyto-chemic analysis, on the contrary, is never safe against irretrievable losses, and this is the more impeding, because those constituents are mostly lost, on the determination of which the success of the whole operation mainly depends. The causes of such losses are either the easy decomposibility, or the volatility, Or the solubility of many organic substances. To avoid such losses must be the incessant endeavour of the analytic operator, if he will not run the risk of losing the fruits of perhaps months of toil.