degrees amalgamated. By this the action is considerably weakened, or ceases altogether; for it is very remarkable that copper, silver, or platina, amalgamated on their surface, have scarcely any, or at most an extremely weak power of keeping up an electric current with any other metal. I have often remarked that the first deviation of the needle was very strong, and that at length it returned quickly to its first position of equilibrium, without exhibiting any deviation, whilst the voltaic circuit, composed of zinc and amalgamated copper, remained always closed. It appears to me also remarkable that a wire of copper, platina, or iron can be much more easily amalgamated under the influence of sulphuric acid by mercury containing other metals than by mercury entirely pure. It is desirable that this point should attract the attention of scientific men to make similar experiments with more attention.
Pure zinc has nearly the same qualities as amalgamated zinc or the amalgam of zinc, viz. of being very little acted upon by sulphuric acid. It is only subjected to chemical action when it enters into a voltaic combination. I refer, on this subject, to the important memoir of M. Aug. de la Rive, inserted in the Bibliothèque Universelle, vol. xliii. 1830. I have not yet been able to procure any pure zinc to repeat these experiments and to employ it in the magnetic apparatus. In zinc foundries pure zinc may easily be obtained in great quantity by re-distilling fit until it is purified of the cadmium and other extraneous metals. Its cost would not be much increased, but hitherto here has not been sufficient inducement to employ pure zinc to risk the expense of the repeated distillation. M. Fengler, manufacturing chemist at Myslowitz in Upper Silesia, has constructed the necessary apparatus for preparing pure zinc in large quantities; he could supply it for nine ecus the quintal, provided a quantity of three quintals were ordered, but unfortunately his foundry has since been burnt down. His process consists in interrupting the distillation when all the cadmium is driven off, in then changing the recipient and again interrupting the process as soon as he suspects that the other foreign metals are volatilized or mechanically drawn away. He repeats these operations as frequently as he thinks necessary. The zinc thus prepared should not be re-cast in iron crucibles.
13.
The rapid decrease of the voltaic effects in the ordinary voltaic piles opposes a great obstacle to the application of electro-magnetism. It may be overcome, partly at least, by an assiduous study of these effects. The motion of my magnetic apparatus was always very rapid at the commencement, but its velocity soon diminished, and ceased entirely after a lapse of time which never exceeded an hour. By employing amalgamated plates of zinc I have succeeded at three different times in making the apparatus work successively during 20, 22, and 24 hours without making any change whatever in the pile. The experiments
