Jl-ke 1, 1883.] 



♦ KNOWLEDGE ♦ 



323 



tell, or guess, what some of these minute beads may really 

 be. Those which are harmless, and those which may give 

 rise to diseases arc not marked out by obvious or striking 

 characters. Many of these organisms become visible if 

 allowed to dry on a slide, and many are very ready to take 



aniline dyes. Minute bacteria, unnoticeable in water, are 

 easily seen as it evaporates, and some arc sure to be found 

 where decomposition is going on. Giving such objects 

 specific names, unless something is' known of their origin 

 or life history, is merely playing with words. 



THE AMATEUR ELECTRICIAN. 



BATTERIES.— I. 



NOTWITHSTANDING the fact that galvanic batteries 

 have been more or loss well known during the past 

 half-century, their functions, and the conditions they are 

 called upon to fulfil are even now, in this " age of elec- 

 tricity," but very imperfectly appreciated by manj' of those 

 whose business or pleasure it is to deal with them. That 

 we are not unduly emphasising this somewhat widespread 

 ignorance is evidenced in many ways, more especially 

 amongst amateurs (a term in which we venture in this 

 particular instance to embrace all who are not engaged as 

 professional electricians). It is no very unusual thing to 

 be asked how many Daniell cells would suffice to maintain 

 a dozen or more incandescent electric lamps, although 

 their inefficiency for the purpose should be apparent to the 

 merest tyro in applied electricity. Then, again, the rela- 

 tive advantages and disadvantages pertaining to the various 

 forms of battery for any particular purpose may to some 

 extent be known, while the causes for such peculiarities 

 are, so far as the experimenter or operator is concerned, 

 enveloped in the deepest oblivion. 



Very frequently the question of applicability resolves 

 itself into one of simple electrical measurement. At other 

 times — and more especially is this the case with modern 

 attempts to " improve " the Daniell battery — the disconti- 

 nuity of the chemical reactions, and the imperfect absorp- 

 tion of nascent hydrogen, result in intermittent currents, 

 whose " pressure " (or electro-motive force) and strength 

 are constantly varying. 



The object in view in these papers is to describe, as 

 succinctly as possible, the principles involved in the con- 

 struction of the various typical forms of battery, giving, 

 at the same time, their numerical efficiency, approximate 

 cost, results of experiments on their durability and utility, 

 and such other matters of interest as may present them- 

 selves, not omitting to furnish details for their simple and 

 inexpensive construction. 



It is desirable, in the first place, that any one who is 

 about to adopt a battery for any specific purpose should 



have a clear conception of the rudimentary principles 

 involved in the doctrine of the " conservation of energy.'" 

 There is not, in the whole range of science, a grander or 

 more universally true doctrine than this, nor is there 

 any similar collection of principles, a knowledge and 

 appreciation of which will prove so useful in protecting 

 one against the allur(;ments of an innumerable ho.st of 

 impostures. Amongst the more recent attempts at " per- 

 petual motion," none are more daring, nor more frequently 

 put forward, than those which are based ou electricity, and 

 scientific lecturers are often guilty of misleading people by 

 statements and experiments, which they, however, probably 

 intended to ha\e a widely ditlerent eliect. For instance, 

 it is often put forth as among the wonderful applicability 

 of electricity that a passing current may be made to 

 simultaneously dellect a galvanometer, raise a weight, 

 decompose water, render a piece of wire or a carbon 

 filament incandescent, and perform a long list of other 

 experiments too numerous to detail. But how many 

 lecturers are there who supplement the experiment by 

 saying that the amount of force expended in all these 

 operations cannot possibly exceed the capacity for per- 

 forming any one of them ; and yet such a law is easily 

 demonstrated. If a current is allowed to pass through the 

 coil of a galvanometer without having any other work to 

 perform, we shall get a dellection of, let us say, 40°. If 

 now we insert an electro magnet in the circuit, the 

 deflection of the needle (or the work performed in forcing 

 it out of the position assigned to it liy gravity) will be 

 sensibly reduced. Here, th^n, is simply and incontro- 

 vertibly demonstrated the fact that a current of electricity 

 can no more be called upon to perform a second kind of 

 work without the first being proportionately reduced, than 

 can a boilerful of steam. Similarly, if we insert an electro 

 magnet in circuit with an incandescent lamp, the luminosity 

 (or the heat developed in the filament) will be propor- 

 tionately reduced. 



The most important battery at present in use is that 

 known as the Daniell, of which there are, as might be ex- 

 pected, a large number of modifications. The principle, 

 however, is never denied to Daniell, who is justly regarded 

 as the father of practical batteries, as the man who con- 

 tributed almost, if not quite as much as Morse or Wheat- 

 stone to make telegraphy a part of every-day life. The 

 size and shape of the to-be-adopted battery will depend 

 considerably upon the requirements of the case. Where 

 the external resistance is low, large plates are required ; 

 and where pottrries are scarce, or electrical instrument- 

 makers exorbitant in their charges, a cylindrical is 

 preferable to a square form. A cell of one quart capacity 

 is perhaps the most generally convenient size. It may be 

 put together very easily. In a glazed earthenware or other 

 non-porous jar place a cylinder of zinc. The zinc should' 

 be about a quarter of an inch thick, and should stand as 

 high as the jar is deep. Where space is not an important 

 factor it will be found cheaper to use a large earthenware 

 pot and a flat piece of zinc, the bending of which is 

 generally troublesome, at least to the amateur. Inside 

 the zinc cylinder place a porous pot, standing half an inch 

 or an inch above the zinc, and containing a sheet of very 

 thin copper, bent into an approximately cylindrical 

 shape. Nearly fill the porous pot with crystals of pure 

 bluestone (sulphate of copper, CuSOj) ; then fill up both 

 the glazed jar and the porous pot to within half an 

 inch or an inch of the top of the outer jar. If re- 

 quired for immediate use, add a small quantity of 

 sulphuric acid to the water in the zinc division, 

 making the proportion about 12 of water to 1 of acid. 

 Terminals, or binding screws, should be attached to the 



