326 Intelligence and Miscellaneous Articles, 



into deutoxide (oxide ferrosoferrique) and mercury into protoxide^ 

 whilst tin and lead are very slightly acted upon by this acid. 



When per-iodic acid is neutralized by carbonate of soda, and pre- 

 cipitated by neutral nitrate of barytes, the resulting liquid is acid ; 

 this is also the case with the neutral salts of lead and lime, indi- 

 cating the precipitation of a subsalt. Per-iodate of lead is white, 

 but becomes yellow by heat, owing to its losing water. Similar 

 phaenomena occur with the proto- and bi-salts of mercury, the 

 former changing from a yellow to a reddish brown, and the latter 

 from white to yellow, by the application of a gentle heat. Peri- 

 odate of soda gives a green precipitate with copper salts, which be- 

 comes more intense by heat, and the proto- and per-salts of iron 

 form yellow precipitates. All these precipitates readily dissolve in 

 dilute nitric acid. — Journ. de Pharmacie, Oct., 1836. 



ON AN EXPERIMENT IN ELECl^RICITY. BY JAMES WATSON, ESQ. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 



As the following experiment may easily be made by any person 

 who has an electrical machine, I think it will be acceptable to many 

 of your readers. 



Take a slip of card about one inch in length and one quarter of 

 an inch in breadth, and at one end of the card make a slit up the 

 middle one quarter of an inch long j then bend out the divided 

 parts in opposite directions, so that the bit of card may be made to 

 stand upright upon its two short legs. By this means the card may 

 be so nicely adjusted that a very slight touch will overbalance it, 

 and cause it to fall. Now take two pieces of stout brass wire, four 

 inches in length and pointed at each end ; bend the wires at right 

 angles, in order that each wire may have a short arm or stem, one 

 inch long. These short arms or stenis are to be inserted a little 

 way into two holes made to receive them in a flat thick piece of 

 wood. The two holes must be made at such a distance from each 

 other that the points ofthetwolong horizontal arms shall be just three- 

 quarters of an inch apart. Midway between these points place the 

 bit of card, in an upright position, c 



as in the figure, where C repre-^ i - i ^ i 



sents the edge of the card, having l\ \ \ \ | ^^ \ 



its two flat sides opposite to the ^\ \^ 



points of the two wires, A and B. ^ ZZ.^ 



To insure success in making this delicate experiment, the machine 

 must be screwed to a very stead?/ table, otherwise the card will be 

 disturbed by the turning of the cylinder. The best way of making 

 the discharge is to suspend a small jar from the prime conductor, 

 and let the jar discharge itself through the electrometer. A chain 

 must connect the electrometer with the wire A, and another chain 

 must connect the outer coating of the jar with the wire B. 



When the experiment is well performed, I always find that the 

 card is perforated, and has a bur on each side of it^ but what de- 



