GALVANISM. 



bodies, when moistened with water, but 

 does not pass at all, except when moisture 

 is present. 



Having given an account of the effects 

 resulting from a single galvanic combina- 

 tion, we will next give some account of 

 the constructions of that compound appa- 

 ratus, termed Galvanic, or, more proper- 

 ly, the Voltaic battery. 



The pile of Volta, of which we have 

 already given a slight description, is at 

 present so little used, that we shall direct 

 our attention more particularly to the 

 trough, as being more convenient for ex- 

 periments than the pile, and at the same 

 time less liable to be out of order. 



The wood of which the trough is form- 

 ed should be the oldest and hardest ma- 

 hogany, being less liable to warp than 

 other kinds of wood. The sides of the 

 trough must be dove-tailed together, and 

 the bottom ought to be grooved into the 

 sides, and fitted in with turpentine ; per- 

 pendicular grooves must be made in the 

 sides of the trough, for the reception of 

 the plates, correspondent to which there 

 must be grooves in the bottom. When 

 the length of a trough is more than two 

 feet, it becomes unwieldly ; it should not 

 even be that length, when the size of the 

 plates would render it too heavy to be 

 handed about. The distance between 

 the plates should be about three-eighths 

 of an inch; if they are nearer together, 

 the acid employed is too soon exhausted, 

 and, consequently, the power of the bat- 

 tery less lasting. 



The plates should be of copper and 

 zinc. Though silver is stronger than 

 copper, it is not so in proportion to the 

 price. 



The 7/1 nc plates are best cut out of 

 sheets of malleable zinc, as being cheap- 

 er, less liable to break, and may be used 

 much thinner. 



The copper may be employed so thin 

 as six ounces to the square foot. 



The plates of copper, being made a lit- 

 .vger than the zinc, may be lapped 

 over the edges of the latter, by which 

 means they fit much closer to the zinc 

 plate, without the labour of hammering 

 the copper plates previously flat. The 

 copper plates only require to be soldered 

 to the upper edge of the zinc plate, since 

 the other three edges are so secured with 

 cement in the grooves as to preclude the 

 necessity of soldering. The lapping over 

 of the copper is sufficient to keep it 

 close to the zinc plate till the plate is 

 fastened in the trough. Previously to in- 

 rrting the plates in the trough, the in- 



side must be lined with a cement, form- 

 ed of resin and bees-wax, or, what is 

 cheaper, of six parts of resin and one of 

 lime and oil. The plates, being previous- 

 ly warmed, are to be pressed down into 

 the grooves before the cement becomes 

 quite cold. After the plates have been 

 inserted, in such order that all the zinc 

 surfaces shall face one way and the cop- 

 per the other, the cement must be more 

 evenly adjusted with a hot iron which 

 will reach to the bottom of the cells; the 

 trough being laid first on one side and 

 then on the other for that purpose. 



When the cementing process is finish- 

 ed, and the whole sufficiently cold, the 

 trough must be dressed oft", and varnished 

 with copal varnish, where it can be had ; 

 but in lieu of that with common spirit 

 varnish. When the varnish is dry, it 

 must be polished with rotten-stone and 

 water. 



In the above construction it is manifest 

 that two of the surfaces are lost by being 

 laid and soldered together. About two 

 years ago the writer of this article had 

 conceived the possibility of making use 

 of both the surfaces of the copper and 

 zinc plates at the same time. According- 

 ly he cemented into a trough, in the 

 groove made for the plates of metal, plates 

 of glass. The metal plates were formed 

 by soldering together a plate of each, of 

 copper and zinc, and then bending them 

 till the plates became parallel to each 

 other, leaving a space between the two 

 surfaces a little wider than the thickness 

 of the glass plates. 



The cells between the glass plates be- 

 ing filled with the proper liquid, each of 

 the above compound plates were made to 

 bestride one of the glass plates, in such 

 order that a zinc and copper plate of two 

 different compound plates, in succession 

 to each other, may occupy each of the 

 cells. All the surfaces are by this contri- 

 vance exposed to the action of the liquid, 

 and might be considered double the pow- 

 er of a common trough, having the same 

 number of plutes. 



Little or no advantage was gained by 

 this method. Though there are two sur- 

 faces of each metal in each of the cells, it 

 will be evident, from several minor expe- 

 riments already given, that two of the 

 surfaces are so completely disconnected 

 as to produce little or no effect. One of 

 the zinc surfaces in this trough is facing 

 the glass on one side the cell, and one of 

 the copper surfaces is similarly situated 

 on the other side. 



The trough, therefore, which is repre- 

 sented in figure 1, and which has been 



