Chemical Science. 379 



determinate proportions was necessary to prevent this electric decom- 

 position, and that mixtures had no influence on the phenomena. 



These results may be important to the mineralogist ; and M. Macaire 

 Prinsep, in illustration, concludes, that the grey cohalt ore of Luna- 

 berg, which is composed of cobalt, arsenic, and sulphur, contains 

 only sulphurets of the metals ; that, on the contrary, the metals 

 of aerolites, although sometimes found associated with sulphur, and 

 always with silica, exist neither as sulphurets nor silicates, but in 

 their metallic condition*, 



5. POWERFUL ELECTRO-MAGNET CONSTRUCTED BY PROFESSOR MOLL. 



If a piece of iron rod be bent into the form of a horseshoe mag- 

 net, and coiled round with a copper wire, so that the latter may form 

 a helix through which the voltaic current may be sent, the iron 

 becomes for the time a powerful magnet. 



Professor Moll has repeated this experiment upon an enormous 

 scale. His galvanic apparatus was a copper cell, charged with 

 water, mingled with ^ of sulphuric and T ^ of nitric acid, into which 

 was introduced a zinc plate exposing 11 square feet of surface to the 

 acid. His magnet was made of a cylinder of soft English iron, 1 inch 

 in diameter ; when bent into form, the interval between the ends was 

 8j inches: the copper wire forming the spiral was i of an inch in 

 diameter, and made eighty-three convolutions ; the weight of the whole 

 was 5lbs. A connecting piece, of the usual form, made of soft iron, 

 joined the two extremities of the horseshoe, and the ends of the spiral 

 were dipped in mercury for ready voltaic communication. The horse- 

 shoe was hung in the usual manner of magnets. 



In the first experiment this arrangement sustained, first, 501bs., and 

 afterwards, with care, 76lbs. by its magnetic attraction. When the 

 suspended weight was small, it was found that the iron retained its 

 magnetism for a time after the voltaic communication was broken. 

 If, instead of merely breaking the direction, the electric poles were 

 reversed, then the reversion of the magnetism took place with ex- 

 traordinary rapidity. On effecting the change, the iron lost all 

 power, the weight fell off, but, with the rapidity of lightning, was 

 again attracted and sustained to an equal amount as at first. 



The rapidity of this change is the more extraordinary, if compared 

 with the slowness and difficulty of charging the poles of a magnet, 

 of equal force, by the ordinary method. If, instead of a heavy weight, 

 a light steel needle be in contact with the poles of the electro-magnet, 

 then so rapid is the change that the needle never falls off, for the 

 attractive force is destroyed and re-established before the gravity of 

 the needle has time to remove it sensibly from its first position. 



\Vlicn the piece of soft iron connecting the poles is held by the 

 hand during this change, the sensation is of the most extraordinary 



Bib. Univ. 1830, p. 146. 



