WIRELESS NEWS.

Press, Volume LX, Issue 18147, 9 August 1924, Page 11

WIRELESS NEWS.

♦ THE OPERATION OF DRY CELLS. CAREFUL USE MEANS GREATER LIFE. (obcullt -warmer jo* "m mas?.") (By "Elytra.") The dry eell as a source of power for radio valves Beem3 to be taken for granted.", One or several are usually connected to a set and then entirely forgotten. Sometimes they last 'a day, sometimes a week, sometimes a few months, and the radio enthusiast may find thorn- a constant source of trouble and irritation, as they may go dead just when least expected or dosired. This need not happen. If radio broadcast listeners would stop to learn a few simple facts about dry batteries it never would, but they aro really not to be blamed, as comparatively little on the subject has appeared in the popular and widely-read radio magazines now published. The Season Why. Therefore in this article, it is my intention to give those who have occasion to use dry cells a little knowledge as to the principle of these colls in the hope that it will enable them to obtain longer and more satisfactory service from their batteries. In understanding why certain phenomena take place they will be in a better position to prevent or assist them. An electric battery is an arrangement for producing electricity in a simple and economical fashion. It makes use of the properties of certain chemicals; and converts the clu<mical energy into electrical energy. Essena battery consists of two dissimilar metal plates immersed and separated in a ehemical solution, which aqts .more rapidly on one than on the other.. If the two plates are joined by a wire so as to form a complete circuit, it will be found that an electric current will flow through this wire. The magnitude of .the pressure which is developed depends, strangely as it may seem, only.on the material rf the plates and the solution, known as the. "electrolyte," and is independent of their «rea.... There are innumerable types of batteries, but in nearly every case one plate is' of zinc arid the other of carbon or copper. The electrolyte can be chosen from a number of liquids. When the battery' becomes exhaust."d, the zinc pfcites and the electrolyte must be renewed,, as the electric current, has been obtained, at their expense. . If we have an elemental cell made up of the. materials just mentioned, a complicated chemical action Bets in, and during it ia generated, among other things', a quantity of hydrogen •;as. This is the same gas balloons are filled with. Now this > hydrogen has a tendency to cling to the carbon or copper plate, and after a few minutes .of use the latter will become more or less covered with the bubbles of it. This will 'prevent the proper functioning of the chemicals,' thus reducing the amount of current .that can be drawn. If the battery is ke«t in service long enough,- the hydrogen bubbles will cover the entire surface I of the carbon, and! make the cell quite 'useless.''.,/ . .'.'; '

Polarisation.

This prdeess Js known as "polarisaand'is v tho, one ■ great problem of battery design. The defect can in part" be overcome by the introduction of other chemicals, which will combine with ; the .hydrogen, to -form, harmless substances, which will not affect the battery action itself. As a matter of fact, the entire value of a battery- depends on the effectiveness df its deprtlarising agent. This is easy, to, Understand,, for if the hydrogen is not disposed of v a useful amount- of electricity will be obtainable- only when' the' battery is first turned .on, which is.when tie plates are i clean.

In addition to covering tne carbon plate and thys'reducing its active Surface, the hydrogen- gas causes.etill another drop jn f the. battery's outpat for in itself it is of high" electrical. re - sistance;, that is, it does not permit even the little remaining electricity to flow through it easily. In some cheap batteries it is astonishing how quickly this action sets in.

'ln commercial'f dry r M cens, sueh, M arc sold for radio and other purposes, the two plates used are o£ : zikt and carbon. • ' . .--•■'••.'•:'

.The zinc, in addition to acting as one of the actual plates.in the chemical, process, serves as the container for the rest of the materials. It is made in the form of an< air-tight shell about six inches'high and two and a half inches in diameter. It is completely lined with a layer of blotting or other absorbent paper. 'ln the eeritire of the shell is set a round carbon stick about fin in diameter, and around it is packed a fine mixture of powdered carbon and manganese dioxide which has been thoroughly soaked in sal ammoniac (ammonium . chloride). The paper lining is similarly, soaked. The sal ammoniac is the electrolyte, and the manganese dioxide the depolarisor. The purpose of the paper lining is to insulate the groand carbon from the zinc, for if these two materials touehed an internal short circuit .would occur.

The carbon rod and the ground carbon act together as one "plate." Thp end of the rod protrudes above the level of zinc, and is equipped with a brass cap and terminal, to which connexion can be made. A layer of sawdust is placed o<rer the mixture and the cells sealed off with Another terminal is soldered to the outside of the zinc, and the whole thing enclosed for protection in a heavy paper case. It may be as well to mention at this point that there is absolutely no difference between round and square dry cells. The insides are exactly the same. The square earfon is sometimes used because it permits orderly stacking of the batteries on a shelf or in' a box. This point is frequently brought up.

"Dry" CeOs Not Dry. Prom the foregoing description it can be seen that "dry" cellfl really aro not dry, bat since the electrolyte is held by the absorbent paper and by the carbon and manganese dioxide mixture, the whole unit can be placed in any position without fear of spilling. However, it -is recommended that dry cells be kept in an upright position wherever possible. The life of a dry battery depends mostly on the electrolyte. Of course, it will be used up by actual me. the dry cells deteriorate even when idle, especially if kept in warm, damp places. The moisture will weaken the solution ix'd lhe waimth will'dry. it. I*ty mast never be allowed to freeze. The carbon is not consumed by ose, i but- the zinc is. A battery fl»eh. has been in service can always »« deteetledbr the white, eaten through spots in the shell. Sometimes, though, the shell lain, fairfy good condition, oven when tire battery can-no longer furnit* carrent. The cell can then bo almost resuscitated by punching holes through the zinc and allowing the whole thing to,soak in a strong solution, of sal ammoniac Tkis ~a*»A old trie*

which often doubles the life of e*n» which otherwise mnst be discarded. A dry battery will behave mash belter if the current drawn is very small* as the effects of polarisation will thsn not bo aa ravishing a« when a heavy current is drawn off in a short space of time. CORSESFONDEHCZ. L.8., Grcymoatht—Satisfactory Jesuits must not bo expected from nngte valve set using a loop serial. I icubt if you would be able to receive say of the New Zealand brondcasthsg stations on the above combination. At least three valves (IRF.-Det-lAF) &r» necessary for obtaining long distaw* results on a loop. t>imeaai«ji» -of a loop with a rango .of approximately 200 to 600 metres are as follows; Outside wire 3ft s<ic-wire wour.4 t* inside—ls turns spaced i inch apart—tap taken off fifth turn from the rentr-, DCC, 18 gauge wire to be vsM. A gaugo smaller or larger will do, ¥>& 300 meters down the first five turn* aw used; for 300 to 800 meteTs use all toe loop. F.J.C, Tcmuka. —Ton certainly havs the wrong connexion for yonr eiwuit, I am forwarding you the correct *oq?:<up. and I think yon should find a hig difference. G.HJ'., Leithficld.-—Tour tremble to certainly very peculiar, and it ia i»possible to givo any opinion en th# matter from the few details in year letter. One can never be certain of the wiring of any radio set aa faalts are always likely to develop, and I would advise yon" to give it the "evm over" if yon have not done so. "Novice."—The higher aerial wfil be by far the better of the two. T&e difference in si2e between the two .wires you mention (7-22 aad 7-80) would not moke enough' diffefeww m Bignal strength to be noticed. SolM wire may be used with the same results as that obtained from the straaded if it ia No. 14 wire or larger. Questions en radio aattar* wffl to answered In this oolasa. HflMrgtW fullest details, ete, and addrm aS correspondence to "HecSra,". cm* ffce Editor, "The Prwo," GfcittlcfcaMt. Beports from readers on tests ©r lasi& distance receiving or any cUwar flusters of interest will b« gladly ncttonL