Observations on Reinsch's test for arsenic / by William Odling.

  • Odling, William, 1829-1921.
Date:
1800-1899
Catalogue details

Licence: Public Domain Mark

Credit: Observations on Reinsch's test for arsenic / by William Odling. Source: Wellcome Collection.

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

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    shoulder, and proceeding backwards to the copper. By this means, the arsenicum was volatilized from the copper, which Fig. l.» resumed its normal appearance, and on examining the capillary termination of the tube, a delicate glistening ring was observa- ble. This, when examined microscopically, with a quarter-inch object-glass, presented a most characteristic appearance. The triangular facets of the crystals, with here and there well-marked octahedra and tetrahedra, truncated and otherwise, were per- fectly recognisable. Any further examination was quite un- necessary ; but to render the experiment as perfect as possible, a minute quantity of sulphide of ammonium was introduced into the capillary tube, so as to reach the deposit. Heat was then very cautiously applied, and a bright yellow ring of orpi- ment obtained, which could be sublimed up and down the capillary tube. The above experiment, which I have frequently repeated, shows that ^th of a grain of arsenious acid can be positively determined by ReinsclTs process, and may be obtained, suc- cessively, as a metallic deposit, a crystalline sublimate, and a yellow sulphuret. This degree of delicacy, though, from the statements of others, and in accordance with my own observa- tion, inferior to that of Marsh's process, is more than sufficient for every practical purpose. Moreover, I believe that even it does not constitute the limit of applicability of the test. In the performance of these minute experiments, it is ex- tremely important that the hydrochloric acid employed should be perfectly pure. It should always be tested, not only for arsenic, but also for nitric acid or free chlorine. I have found many specimens of miscalled pure hydrochloric acid, which bleached sulphate of indigo; and, only within this last week, by employing unwittingly an acid of this description, was 1 Fig. 1 is a somewhat enlarged representation of the above-described subliming tube. A indicates the copper gauze ; B, the crystalline sublimate.