VOLTAIC ELECTRICITY. 



Many other forms of batteries have been constructed by dif- 

 olootricians, which have their own special advantages ; 



I. ut ..wintf to various causes they have not oomo into 



, therefore, be described in a series of I 

 prc-i -lit. T!H.TO are, however, one or two more which 

 nlmuld be referred to. 



If wo take a good black-lead crucible, and expose it fr a 

 M:.' to u l.ritflit rod boat, wo shall bo ablo to construct 

 in it. 



A wire must bo twisted tightly round the exterior of tho era- 

 cililf, HO as to ensure a good contact, un-l tins \\iro will be the 

 re polo. A porous cell is then |>l.i'-< I in tho crueiMe, 

 .UK I iusidu this cell a plate 

 or rod of amalgamated 

 /.inc. Nitric acid is then 

 1 into tho outer cell, 

 uml dilute sulphuric into 

 tin- inner, and our battery 

 iuplcto. Tho carbon, 

 however, in the crucible is 

 not very pure, and thus 

 does not form a good eon- 

 r ; tho power is, there- 

 much less than can 

 bo obtained from a cell of 

 's. 



The Maynooth Battery 

 is one in which cast-iron 

 iiml zinc are employed. 

 In it the outer cell is con- 

 structed of cast-iron, and is 



mode water-tight. Inside this the porous cell, with the zinc plate 

 i:i it, is placed in the usual way. Tho iron cell is charged with 

 si mixture of strong nitric and sulphuric acids, the other with 

 two parts of sulphuric, one of nitric acid, and about eighteen or 

 twenty of wiiler. The power of this combination slightly ex- 

 ceeds that of those previously described ; but it is not quite so 

 convenient, and evolves a larger amount of nitrous acid vapour, 

 which renders it very unpleasant to use. 



In all these forms of battery two different metals arc used ; 

 we must, however, notice a different kind, which depends for its 

 action on the power which certain metals possess of condensing 

 gases at their surfaces. It is known as Grove's Gas Battery, and 

 though rarely if ever used in 

 practice, is interesting, as it 

 explains several phenomena 

 which are met with at 

 times. Two glass tubes are 

 taken, and are sealed at 

 their upper ends, wires of 

 platinum being fused into 

 the glass. Inside the tubes 

 are strips of platinum con- 

 nected with these wires. 

 One tube is now filled with 

 hydrogen and tho other 

 with oxygen gas, and both 

 are inverted over a vessel 

 of dilute sulphuric acid. 

 If wires be now connected 

 with the platinum in tho 

 ends of each tube, a current 

 will pass along them, as may 



procure or make for themselves one of some of the kinds referred 

 to. The first point, and one that cannot be too strongly im- 

 pressed upon the mind in the use of all electrical apparatus, is 

 the absolute necessity for all connections to be most thoroughly 

 clean. 



Much of the intensity of the current is lost if any particle of 

 non-conducting material of any kind be interposed in 

 the circuit. Band.paper and the file are, therefore, among 

 the most important of oar tools, and should ever be found 

 at a convenient place in the laboratory, and be kept hi 

 constant use. Let the ends of wires be always craped or 

 nibbed with sand-paper before being connected to any piees 



of the apparatus, and let 

 the binding screws be 

 cleaned, and the hole* in 



th. Mi : :ir.-i L> BMHi ..f a. 



rat's-tail file before using 

 them. These appear bat 

 trifling natters, but often 

 the success of an experi- 

 ment or the working of a 

 well-made instrument is 

 greatly impaired and much 

 valuable time wasted by 

 the neglect of these little 



-,. oft 



The next point to be 

 noticed is this, that when 

 a battery is taken down 

 to be put away it should 

 be carefully rinsed oat. 



The acids may be saved if they have only been used for a short 

 time ; but where two acids are used, and the cells have been in 

 action for an hour or so, there is little, if any, saving effected by 

 this, for tho acids mix slightly through the porous cell, and the 

 mixture eats away the zinc much more rapidly than the single 

 acid does. If the cells are emptied into a jug, any mercury 

 which is at tho bottom of them will be saved. 



The porous cells should be put in a pail of water, as the 

 sulphate of zinc or (in the case of Daniell's) the sulphate of 

 copper becomes absorbed by the cell, and when it is allowed to 

 dry crystallises in an efflorescent manner round the tup, often 

 chipping or cracking the cells. The zinc likewise should be 



kept well amalgamated, as 

 otherwise it soon beooniss 

 eaten into holes. 



We may mention here 

 that it is not absolutely 

 necessary for two different 

 metals to be employed in 

 the construction of a bat- 

 tery, as a slight current 

 may be produced by em- 

 ploying two plates of the 

 same metal zinc, for in- 

 stance one of which is 

 quite new and smooth, 

 while the other is rough 

 and worn. Even with a 

 single plate a current may 

 be obtained if one part of 

 the plate be in one liquid 



Fig 21. and the rest in another. 



In illustration of this we 



easily bo shown by means 



of a galvanometer. While tho current is passing the volume of ; give a neat experiment for the student to try. 



the gases in the tubes slowly diminishes the hydrogen, of course, ; Take a glass vessel, and fill it about onerthird full with a strong 



going twice as fast as the oxygen ; the tube containing it should solution of sulphate of copper (blue vitriol), and on the top of 



therefore be double the size of the other. In this form of ; this pour very carefully a solution of salt and water, or some 



battery the current passes from tho tube containing the oxygen dilute acid, taking care not to let the liquids mix. Now place a 



to that containing tho hydrogen. The platinum plate acts strip of zinc in the vessel, so that a part may be in each soln- 



moro powerfully if its surface be somewhat roughened by de- I tion, and the existence of the current will soon be shown I 



positing a little finely powdered platinum on it. The theory of appearance of a deposit of metallic copper on the part of the 



the action does not appear to be fully understood, but tho spongy zinc which is in the solution of that metal. 



platinum ring sometimes used to ignite hydrogen gas is another Having now seen the way in which we procure our 



illustration of the same effect. force, we shall have to notice in our next lessons the 



Having thus described the forms of battery in most general produced by the combination of several cells, the way jn whic 

 nse, it will be well to give a few general hints as to their manage- we can convey the current to any required place, and the 

 ment, more especially as we hope that many of our readers will I which wo can cause it tu produce. 



