TO THE MOVEMENT OF MACHINES. 521 



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 de^dation of the needle was 

 very strong, and that at length it returned quickly to its first position 

 of equilibrium, Avithout exhibiting any deviation, whilst the voltaic cir- 

 cuit, composed of zinc and amalgamated copper, remained always 

 closed. It appears to me also remarkable that a wire of copper, pla- 

 tina, 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 atten- 

 tion 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 

 INI. Aug. de la Rive, inserted in the Bibliotheque IJniverselle, 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 foun- 

 dries pure zinc may easily be obtained in great quantity by re-distilling 

 fit until it is purified of the cadmium and other extraneous metals. 

 I Its cost would not be much increased, but hitherto there has not been 

 [sufficient inducement to employ pure zinc to risk the expense of the 

 [repeated distillation. M. Fengler, manufacturing chemist at Myslowitz 

 f Jn Upper Silesia, has constructed the necessarj' apparatus for preparing 

 [pure zinc in large quantities; he could supply it for nine ecus the 

 I quintal, provided a quantity of three quintals were ordered, but unfor- 

 I tunately 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 mecha- 

 nically 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 ha\e succeeded at three different times 

 in making the apparatus work successively during 20, 22, and 24' hours 

 without making any cliange whatever in the pile. The experiments 



