VIII. On a simple electro-chemical method of ascertaining the presence of different metals; applied to detect minute quantities of metallic poisons

Abstract

It is now nearly a quarter of a century since the late Sir Humphry Davy, by a train of masterly researches, developed the general principles of electrochemical action, which subsequently led him to many fine discoveries and important practical applications. Some years since, I repeated most of the interesting experiments noticed in his excellent Bakerian Lecture “On the chemical agencies of Electricity.” On the decomposition of metallic salts by the Voltaic battery, Sir Humphry is very brief. He clearly ascertained, however, that “when metallic solutions were placed in the circuit, metallic crystals or depositions were formed on the negative surface;" and that “the metals passed towards the negative surface, like the alkalies, and collected round it.” In the course of my experiments on this subject, phenomena occurred which led me to think that some novel results might be obtained by instituting a series of experiments on metallic salts, using as a Voltaic arrangement the feeble power produced by the contact of small slips of different metals, with solutions of the common metallic salts. Operating in this manner, I could readily detect very minute quantities of different metals, coat platina with gold, silver, copper, &c., or cover gold with a surface of these metals, and tin, copper, brass, iron, &c. Several of those facts I have been in the habit of bringing forward and illustrating in my annual courses of lectures delivered both in the Royal Cork Institution, and in the Royal Dublin Society. Circumstances which it is unnecessary to mention, have hitherto prevented me from giving greater publicity to those facts. In the course of the present summer my attention has been directed to apply similar means to the detection of metallic poisons, a subject of acknowledged and increasing importance; and the results I have obtained, and now beg leave to submit to the Society, appear to me both novel and interesting, and afford, if I mistake not, means more simple, delicate, and effectual, than any at present known for detecting the common metallic poisons. The fear of trespassing too much on the time of the Society, induces me to limit the present paper to one part only of the subject. At no distant period I promise myself the pleasure of communicating the remaining part, which will embrace the different electro-chemical experiments I have made on the other metals and their compounds, together with the application of the facts to the processes of gilding, silvering, tinning, &c.