Oct. 16, 1884] 



NA TURE 



587 



undoing diffusion, which is impossible, but because during 

 each charging fresh acid is formed, and in great part falls 

 to the bottom in visible streams. Another great advan- 

 tage was that some amount of inspection of the plates 

 became possible, and experience as to the actual behaviour 

 and appearance of the plates, began to be accumulated. 

 And painfully varied that experience was. Every variety 

 of extraordinary behaviour which could be suggested as 

 probable, and a good many which no one could possibly 

 have imagined beforehand, made their appearance. The 

 hundreds of tons of batteries made at this period doubt- 

 less enabled these unpleasant experiences to be more 

 rapidly acquired than would have been done on a small 

 scale, but it was a costly series of experiments. However, 

 the experiments were made, the public involuntarily 

 assisted in the acquisition of experience, and, caring less 

 for knowledge than for marketable commodities, they 

 expressed dissatisfaction at the result. Many of these 

 incipient difficulties are now overcome by the manufac- 

 turers, but the great dislike of the public to involuntary 

 experiments, and the shock which their confidence under- 

 went on being unexpectedly called upon to participate in 

 research, have not yet altogether abated. 



The main difficulty now experienced was how to keep 

 the plates from touching. They might be put in wooden 

 frames, or elastic bands might be stretched round each 

 of them, and if the)' would only keep flat it was impos- 

 sible they should touch unless the composition should 

 drop out of the holes. Sometimes the composition did 

 drop out of a hole, and bridge across the interval between 

 two plates, but the more common and more fatal ex- 

 perience was that the plates would not keep straight. In 

 a few months the positives were found to swell, and as 

 they swelled to buckle — to buckle and twist into every 

 variety of form, so that elastic bands, wooden frames, 

 and every other contrivance failed altogether to prevent 

 short-circuiting. The cause of the buckling is of course 

 irregular and one-sided swelling, and the cause of the 

 swelling is apparently the gradual peroxidation and sul- 

 phating of the material of the bars of the lead grid, which 

 occupy less room as metallic lead than as oxide or salt. 

 As the bars swell, they press on the inclosed composition, 

 occasionally driving it out, but more frequently, and with 

 properly made and treated plates universally, distending 

 themselves and stretching the whole medial portion of the 

 plate. The edge or frame of the grid is stronger than the 

 middle bars, and is not so easily stretched ; in a good and 

 uniformly worked plate it does stretch, and an old posi- 

 tive plate is some quarter of an inch bigger every way 

 than a new one, but if one face of the plate is a trifle 

 more active than the other, it is very plain that the most 

 active side will tend to become convex ; and buckling once 

 begun very easily goes on. To cure it two opposite 

 plans have been tried : one is to leave the plates as free 

 and unconstrained as possible, hanging free it may be 

 from two points, thin, and with crinkled or crimped 

 margins to allow for expansion ; the other is to make 

 them thick and strong, with plentiful ribs for stiffness, and 

 besides to clamp them up one to another as tightly as 

 may be, and thus in mechanical ways to resist buckling and 

 distortion. I do not know that any one could say for certain 

 beforehand which of these two plans would be likely to 

 answer best, but practice is beginning to reply in favour of 

 the latter, and well braced plates of fair thickness show no 

 unmanageable tendency to buckle. It must be remem- 

 bered that no material can buckle with a force greater 

 than that necessary to restore it to flatness, and this force 

 in the case of lead is very moderate. Hence it may be 

 fairly hoped to overcome and restrain all exuberances by 

 suitable clamps and guides arranged so as to permit flat 

 and even growth, but to check all lateral warpings and 

 excrescences. 



Uniformity of action is still essential, especially if all 

 the plates in a cell are clamped together. Plates mechani- 



cally treated alike ought to be electrically so treated also, 

 and it is impossible to keep a set of plates working satisfac- 

 torily together unless the contact of each is thoroughly and 

 equally good, so that each may receive its fair share of cur- 

 rent. Defects of contact havebeen a fruitful source of break- 

 down and irregularity. Clamps and screws of every 

 variety have been tried, but the insidious corroding action 

 of nascent oxygen exerted through the film of acid which 

 by spray and creeping forms and concentrates on the 

 lugs — this corroding action crawls between the clamped 

 surfaces, gradually destroys all perfect contact, and some- 

 times produces almost complete insulation. Contacts on 

 the negative plates give but little trouble ; contacts on 

 the positives have taxed a great amount of patience. 

 Lead contacts " burned," i.e. melted, not soldered on, are 

 evidently less liable to corrosion than brass or copper 

 fittings, or than any form of clamp, but they are apt to be 

 somewhat clumsy if of sufficient conductivity, and more- 

 over they are awkward to undo again, and somewhat 

 troublesome to do. However they have proved them- 

 selves so decidedly the best that now no other contacts will 

 be used, and their re-introduction has been followed by a 

 marked improvement in the behaviour of the cells. So long 

 as contact with one plate was better than with another, a 

 thing quite possible to happen without any difference being 

 perceptible to the eye, so long was it possible for one or 

 two plates to remain almost wholly inactive while another 

 one or two received far more than their share of current, and 

 became distended, warped, overcharged, and ultimately 

 crumbled away. If one or two plates in a cell are black, 

 and giving off torrents of gas, while the rest are brown 

 and idle-looking, it is pretty fair evidence of irregular and 

 insufficient contact, or else of some great discrepancy in 

 the age or make of the plates. This point also is one that 

 was not attended to in the early stages of manufacture ; 

 plates were made for stock, and cells were made up with 

 plates of all ages selected at random from the store. 

 Directly uniformity is perceived to be essential, this is 

 recognised as obviously bad. Plates intended to work 

 together should be of the same age and make, and inas- 

 much as keeping does not improve them, the best plan is 

 not to make for stock, but to keep material ready, and then 

 quickly make up as wanted. Plates in work deteriorate 

 slowly, but the)' are wearing out in the fulfilment of their 

 proper function ; plates in idleness deteriorate as quickly, 

 and they are rusting out in fulfilment of no function at 

 all. Worn-out plates, however, are by no means value- 

 less. Lead material has a well recognised price, and if 

 attention were given to the subject, it is probable that 

 decrepit and useless plates might be made to yield a very 

 large percentage, if not the whole, of their original lead. 

 For it must be remembered that plates deteriorate not 

 by waste but by accretion : an old plate contains as 

 much lead as a new one, but it contains it with the addi- 

 tion of oxygen and sulphion ; no longer a tenacious 

 coherent frame, but a crumbling mass of incoherent 

 powder. 



The age of plates is a point of vital interest, though 

 but little is known as to the possibilities in this direction 

 at present. A year may be regarded as a fair average 

 age at the present time ; but this is a low rather than a 

 high estimate. Thick plates are found to last far longer 

 than thin, which is only natural when it is remembered 

 that the wearing out is due to corrosion, that corrosion 

 proceeds mainly from the surface inwards, and that the 

 internal portions of a thick plate are to a great extent 

 protected by the mass of superincumbent material. If it 

 can be shown, as we understand it can, (1) that the cost of 

 materials is far more than the cost of manufacture ; (2) 

 that the worn-out material has a market value not in- 

 comparably less than the original ; and (3) that the 

 frequency with which plates have to be renewed is not 

 such as to cause much inconvenience ; then we hold that 

 the first stage of the durability difficulty has been over- 



