Chemical Science. 185 



upper end passing through the cork to the upper surface ; 

 the slip of copper is the sanne width as the zinc, but passes 

 round the zinc, being opposed to both its surfaces as in Dr. 

 Wollaston's construction, its upper end also appears through 

 the cork, A piece of copper wire, covered with silk thread, is 

 coiled five or six times, and tied together, so as to form a ring 

 about an inch in diameter, and the ends of the wire are con- 

 nected, one with the zinc, and the other with copper slip above 

 the cork. When this small apparatus is placed in water 

 slightly acidulated by sulphuric acid, the voltaic apparatus is 

 active enough to make the ring highly magnetic ; and by pre- 

 senting a magnet to it in different directions, it may be at- 

 tracted or repelled, and presents all the phenomena of a mo- 

 bile conducting wire. 



The other apparatus is also a little voltaic combination hung 

 from a cork, but the plates are connected together, not by a 

 ring of wire, but by a helix. The helix is made of similar wire 

 to the ring, it is about one-third of an inch in diameter, and the 

 two ends of the wire are returned through the helix till near 

 the middle, when they are made to pass to the outside between 

 the spirals, then being connected with the upper ends of the 

 plates, the helix lies on the cork, with its two ends equally 

 distant from the centre, the course of the electricity being along 

 the wire, from one end of the helix to the other, and then back 

 to the plates. When placed on acidulated water the helix be- 

 comes magnetic, and its extremities become opposite magnetic 

 poles, being attracted and repelled by the poles of a magnet, 

 just as another magnet would be in the same situation. — Bib. 

 Univer. xvi. p. 201. 



These little instruments took their rise from the floating 

 needle of M. Naef. This was composed of a strip of silver 

 and one of zinc connected together, bent, and floated on cork. 

 These, when placed on acid, were attracted and repelled by 

 the magnetic pole. — Bib. Univer. xvi. p. 120. 



18. Contact in Voltaic JF/cc<nci^»/.— In making experiments 

 in voltaic electricity and electro-magnetism, where numerous 

 repetitions of contact between wires are required, it is ex- 

 tremely useful, if these wires are copper, to rub the ends over 

 with a little nitrate of mercury ; an amalgam is thus formed on 

 ilie surface of the copper, which does not oxidate or become 

 dirty as copper itself does, but remains bright, and fit for voltaic 

 contact for a long time. M. F. 



19. Magnetism Inj Electricity. — M. Van Bcch has remarked, 

 that a very slight degree of common electricity is sufficient to 

 produce magnetism in a needle. A helix was made, and an un- 

 magncti/ed needle placed in its interior ; then one end being 

 held in the hand, tlie other was brought near tiie conductor of 



