Electric Bells and All About Them

by the acid, being rapidly corroded and dissolved, while at the same time a quantity of bubbles of gas are seen to collect around, and finally to be evolved at the surface of the fluid in contact w

like a letter Λ, or by connecting the upper extremities together by means of a piece of wire (or other conductor of electricity), or by causing their lower extremities in the fluid to touch, we notice a very peculiar change. The extrication of bubbles around the zinc strip ceases entirely or almost entirely, while the other strip (silver, copper, or graphite) becomes immediately the seat of the evolution of the gaseo

cumstances) has a considerable influence on the efficiency of a battery, it is well to unde

a strongly electro-negative portion, which may either be a single body, such as chlorine, iodine, bromi

bromine, iodine, etc., respectively by Cl., Br., and I., the constitution

H B

┗━━

ochl

]. Hyd

Hydr

c

of 1 atom of sulphur and 4 atoms of oxygen, united to 2 atoms of hydrogen) or nitric acid (consisting of 1 nitrogen

O4

━┛

phu

]. and

id

ts characteristic sourness and corrosiveness, becoming, as chemists say, neutralized. One atom of zinc can replace two atoms of h

ssed also by many other bodies, and is of very common occurrence in chemistry; and may be roughly likene

are used to excite electricity by their behaviour along with zinc, the follow

Zinc, equal Zinc Chl

Zn = Zn

r

inc, equal Zinc Sulp

Zn = Z

in which zinc is acted on by a compound body containing hydrogen, rep

2X = Z

orrosion and solution of the zinc, and the

ter were doing work or not. For this reason the use of commercial zinc, in its ordinary condition, is not advisable in batteries in which acids are employed, since the zinc is consumed in such, whether the battery is called upon to do electrical work (by placing its plates in connection through some conducting circuit) or not. This serious objection to the employment of commercial zinc could be overcome by the employment of chemically purified zinc, were it not that the price of this latter is so elevated as practically to preclude its use for this purpose. Fort

o salivation, etc.; and, secondly, because any jewellery, etc., worn by the wearer will be whitened and rendered brittle. When the entire surface of the zinc becomes resplendent like a looking-glass, the rubbing may cease, and the zinc plate be reared up on edge, to allow the superfluous mercury to drain off. This should be collected for future operations. It is important that the mercury used for this purpose should be pure. Much commercial mercury contains lead and tin. These metals can be removed by allowing the mercury to stand for some time in a vessel containing dilute nitric acid, occasional agitation being resorted to, in order to bring the acid into general contact with the mercury. All waste mercury, drainings, brushings from old plates, etc., should be thus treated with nitric acid, and finally kept covered with water. Sprague, in his admirable work on electricity, says:-"Whenever the zinc

ts of mercury (by weight) for every hundred of the zinc thus weighed up. The zinc should then be melted in a ladle, with a little tallow or resin over the top as a flux. As soon as melted,

ss a very considerable time be allowed for the mercuric salts to act, is neither so deep nor so satisfactory as in the case of mercury alone. It may here be noted, that although the effect of mercury in protecting the zinc is very marked in those batteries in

ate, we shall find that it is literally covered with a coating of small bubbles of hydrogen gas, and, if we agitate the liquid or the plates, many of them will rise to the surface, while the magnetic needle will at the same time give a larger deflection. If we entirely remove the plates from the acid fluid, and brush over the surface of the copper plate with a feather or small pledget of cotton wool fastened to a stick, we shall find, on again immersing the plates in the acid, that the effect on the needle is almost, if not quite, as great as at first; thus proving that the sudden loss of electrical energy was greatly due to the adhesion of the free hydrogen gas to the copper plate. This peculiar phenomenon, which is generally spoken of as the polarisation of the negative plate, acts in a twofold manner towards checking the electrical energy of the battery. In the first place, the layer of hydrogen (being a bad conductor of electricity)

t until all the zinc be consumed or all the acid exhausted, some device for removing the liberated hydroge

This mode was adopted by Smee in the battery which bears his name. It consists of a sheet of silver, pl

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the plain zinc and smooth copper form. A modification of Smee's battery which, owing to the large negative surface presented, is very advantageous, is Walker's graphite cell. In this we have a plate of zinc between two plates of gas-carbon ("scurf"), or graphite. The surface of this body is naturally much rougher than meta

ell; and the battery known by his name still retains its position as one of the simplest and best of the "constant" forms of battery. The term "constant," as applied to batteries, does not mean that the battery is a constancy, and will run for ever, but simply that so long as there is in the battery any fuel (zinc, acid, etc.), the electrical output of that battery will be constant. The Daniell cell consists essentially in a rod or plate of zinc immersed in dilute sulphuric acid, and separated from the copp

O4 = ZnS

id produce zinc sulph

the copper is, it turns the latter out, takes its place, setting the copper free, and forming, with the sulphur oxide, sulphuric acid. The liberated copper goes, and adheres to the copper plate, and, far from detracting from its efficacy, as the liberated hydrogen would have done, actual

O4 = H2S

sulphate produce sulphu

Daniel

dilute sulphuric acid. A containing vessel, V, of glazed earthenware, provided with a perforated shelf, S, on which are placed the crystals of sulphate of co

, is also constructed, and known as "Minotto's" cell: this, owing to the greater thickness of the porous layer, offers more resistance, and gives, consequently, less current. By taking advantage of the greater specific gravity (weight, bulk for bulk) of the solution of sulphate of copp

Gravit

ed to rest a thick disc of zinc, Z. Speaking of these cells, Professor Ayrton, in his invaluable "Practical Electricity," says:-"All gravity cells have the disadvantage that they cannot be moved about; otherwise the liquids mix, and the copper sulphate solution, coming into contact with the zinc plate, deposits copper on it. This impairs the action, by causing the zinc to act electrically, like a copper one. Indeed, without any shaking, the liquid

mention nitric acid, which readily parts with a portion of the oxygen (§ 18) and reconverts the free hydrogen into water. This acid is used as the "depolarizer"[9] in the "Grove" and in the "Bunsen" cell. Another very energetic "depolariser" is

This latter oxide forms the basis of one of the most useful cells for electric bell work, namely: the one known as the "Leclanch

, the porous cell itself being placed in an outer containing vessel, which usually takes the form of a square glass bottle. A zinc rod stands in one corner of the bottle, and is prevented from coming into actual contact with the porous cell by having an indiarubber ring slipped over its upper and lower extremities. The glass co

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corrode the terminal, and thus oppose resistance to the passage of electricity, the upper end of the carbon, before the lead cap is cast on, is soaked for some time in melted paraffin wax, at a temperature of 110° Centigrade: that is somewhat hotter than boili

ammonium is able, by virtue of its electrical charge, to displace the ammonium from the combined chloride. In so doing, it sets the liberated ammonium in an electro-positive condition, as it was itself, losing at the same time its electrical charge. This interchange of molecules goes on (as we saw in the case of the Daniell's cell, § 24) until the surface of the carbon is reached. Here, as there is no more ammonium chloride to decompose, the ammonium 2NH4 immediately splits

inc comp

l = ZnCl2

de of mangane

O2 = Mn2

be the case, more sal ammoniac must be added. It is found that for every 50 grains of zinc consumed in this battery, about 82 grains of sal ammoniac and 124 grains of manganese dioxide are needed to neutralize the hydrogen set free. It is essential for the efficient working of this battery that both the manganese dioxide and the carbon

he battery employed should be a thoroughly reliable one and set up in a proper manner, as a failure in the battery causes a breakdown in the communication throughout the whole building, whilst the failure of a push or wire only affects that portion of the building in which the push or wire is fixed. A common fault is that of putting in (with a view to economy) only just enough cells (when first set up) to do the necessary work. This is false economy, as when the cells are but

imply placing the carbon and manganese together loosely in a porous cell, solid blocks are formed by compressing these materials, under a pressure of several tons, aroun

.

dioxide

gas carbo

resin

.

xide (pyrolus

(powdered

resin

bisulpha

ining the central carbon core) at a temperature of 100° C. (212° Fahr.),

.

d Leclanch

dioxide

te 44

rai gras"

ur ?

r ?

temperature of which is gradually raised to about 350° C. (about 662° Fahr.); a temperature which is insufficient to decompose the depolarising substance (manganese dioxide), but sufficient to drive out first the volatile parts of the agglomerating material, and then to transform its fixed parts in a body unattackable by the ammonia of the cell. During the gradual heating, or baking, which lasts about two hours, what remains of the water in the agglomerate is driven off; then come the more volatile oils contained in the pitch, and finally the sulphur. The sulphu

g.

c, separated from actual contact with the carbon by means of a couple of crossed indiarubber bands, which serve at the same time to ho

e agglomerate form of Leclanché over the or

d to the best advantage, and that, owing to this, the ele

cell, there is less internal resistance in the

battery remains pretty constan

into contact with both elements immediately, the

y, since the elements can be removed together, fresh s

pt when several bells are arranged in parallel, so that a large current is required. The blocks certainly polarise more quickly than the old form, and it does not appear that they depolarise any more rapidly. Probably the enormous pressure to which the blocks are subjected, in the first two processes, renders the composition almo

locks prepared by process No. 3, but he is under the impression that the bl

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cell by Prout's elastic glue, or some similar compound, so as to leave spaces, which are filled in with granular carbon and manganese. The surface of the plates is perforated, so as to allow ready access to the exciting fluid. The zinc rod, which is affixed to the cover, stands in the centre of the cell, touching it at no part. O

or three-pint, size. No. 2 is always quart size, and this is the one commonly employed. When several cells are employed to work a number of bells, it is well, in order that they may not receive injury, that they be enclosed in a wooden box. As it is necessary that the ba

Battery

onsists in filling in the neck with melted pitch, two small funnel-like tubes being previously inserted to admit of the addition of fresh sal ammoniac solution, and for the escape of gas. This mode cannot be recommended, as it is almost impossible to remove the pitch (in case it be required to renew th

g.

atentees:-"All who have had experience of batteries in which a solution of salts is used are aware of the difficulty experienced in preventing it creeping over the outside of the jar, causing local loss, and oftentimes emptying the jar of its solution. Many devices have been tried to prevent this, but the only effectual one is our patent insulated jar, in which a recess surrounds the top of the jar, this recess being filled with a material to which the salts will not adhere, thus

ttery. It is of the utmost importance to the effective working of any battery that not the slightest leakage or local action should be allowed to take place. However slight such loss be, it will eventually ruin the battery. This leakage may be taking place in the battery, as a porous cell may be broken, and carbon may be touching the zinc; or

e stoneware jar, the space between the two being packed with broken carbon and manganese dioxide. By this means a very much larger negative surface is obtained. In the Grenet cell, the porous cell is replaced by a canvas bag, which is p

Cr, and oxygen by O, we can get a fair idea of its constitution by expressing it as K2Cr2O7, by which it is shown that one molecule of this body contains two atoms of potassium united to two atoms of chromium and seven atoms of oxygen. Bichromate of potash readily parts with its oxygen; and it is upon this, and upon the relatively large amount of oxygen it contains, that its efficiency as a depolariser depends. Unfo

O4 + H2O = K2

━┛ ┗━┛ ┗

acid. & 1 molecule of water. give 1 molecule of

chromic acid in these batteries; the more so as chromic acid is extremely soluble in water. In the presence of the hydrogen evolved during the action of the battery (§ 18) chromic acid parts with a portion of its oxygen, forming water and sesquioxide

3H2 = 5H

┗━┛ ┗━

es of hydrogen. give 5 molecules of wate

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lates, electrically connected to each other and to one of the binding screws on the top. Between these two plates is a sliding rod, carrying at its lower extremity the plate of zinc. This sliding rod can be lowered and raised, or retained in any position, by means of a set sc

t Re

mate S

potash (finely

water

to cool, then add, in a fine

acid (oil of vi

a glazed earthern vessel, an

nd R

Acid S

(chromic tr

r 1

ssolved, then add gra

ric ac

st not be us

filled with the exciting fluid, to allow plenty of room for

utting a small quantity of mercury in the porous cell. The porous cells must be paraffined to within about half an inch of the bottom, to prevent too rapid diffusion of the liquids, and the cells themselves should be chosen rather thick and close in texture, as otherwise the zinc will be rapidly corroded. Water alone is used as the exciting fluid in the porous cell along with the zinc. Speaking of this form of cell, Mr. Perren-Maycock says:-"The base of the zinc is more acted on (when bichromate crystals are used), because the porous cells rest on the crystals; therefore let it be well paraffined, as also the top edge. Instead of paraffining the pot in strips all round (as many operators do) paraffin the pot all round, except

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ven to the modification of the Fuller c

here the strain or tension is less. In a cell in which zinc and carbon, zinc and copper, or zinc and silver are the two elements, with an acid as an excitant, the zinc during the action of the acid becomes of higher "potential" than the other element, and consequently the undulations take place towards the negative plate (be it carbon, copper, or silver). But by this very action the negative plate immediately reaches a point of equal tension, so that no current is possible. If, however, we now connect the two plates together by means of any conductor, say a copper wire, then the strain to which the carbon plate is subjected finds its exit along the wire and the zinc plate, which is continually losing its strain under the influence of the acid, being thus at a lower potential (electrical level, strain) than the carbon, can and does actually take in and pass on the electric vibrations. It is therefore evident that no true "current" can pass unless the two elements of a battery are connected up by a conductor. When this connection is made, the circuit is called a "closed circuit." If, on the contrary, there is no electrical connection between the negative and positive plates of a cell or battery, the circ

ed 32°F. as long as it remains ice; and whether we cause a pint or a thousand gallons of water to boil (under ordinary conditions), its temperature will not exceed 212°F. The only means we have of increasing the E.M.F., or "tension," or "potential," of any given battery, is by connecting up its constituent cells in series; that is to say, connecting the carbon or copper plate of the one cell to the zinc of the next, and so on. By this means we incre

6

·

·

vo

tromotive force o

g.

sistance opposed by the narrowness of the tube to a greater flow. If now we double the capacity of the exit tube, leaving the pressure or "head" of water the same, we shall double the flow of water. Or we may arrive at the same result by doubling the "head" or pressure of water, which will then cause a double quantity of water to flow out against the same resistance in the tube, or conductor. Just in the same way, if we have a given pressure of electric strain, or E.M.F., we can get a greater or lesser flow or "current" by having less

ciated the following law, which, after him, has been called "Ohm's Law." It is that if we divide the number of electromotive force units (volts) employed by the number

omotive force/Res

s, and ohms, instead of the general terms, E, R, a

resistance. This resistance is known as "internal resistance," and must always be reckoned in these calculations. We can halve the internal resistance by doubling the size of the negative plate, or what amounts to the same thing by connecting two similar cells "in parallel;" that is to say, with both their zincs together, to form a positive plate of double size, and both carbons or coppers together to form a single negative of twice the dimensions of that in one cell. Any number of cells thus coupled together "in parallel" have their resistan

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E.M.F. AND R

apacity of Cell

Volts.

O

2 quarts

vity 2 quar

é 1 pint

2 pints

3 pints

te 1 pint

te 2 pint

te 3 pint

quart 1

vity Daniell were employed the current flowing in the same wire would only be a little over 1/10 of an ampère, since 1·079/10 = 0·1079. But every wire, no matter how short or how thick, presents some resistance; so we must alwa

stream, with constant stirring, to the water, and not the water to the aci

irits

l of v

quafo

t up a current

ny body which, by absorbing the free hydrogen, r