Crompton. doing so with any material that is not attacked, but the method Mr. Α I wish to call attention to Mr. Swinburne's figures as to the comparative bulk of peroxide of lead, red lead, litharge, and lead sulphate. Those figures are very instructive, if they are correctly shown, and if the lead sulphate is to peroxide as 297 is to 160, it of course points out very clearly the cause of the buckling and twisting of the plates, which has been one of the greatest difficulties we have had to meet. At one time a great many of my experiments were made with porous lead plates,plates which had been cast in such a manner that they crystallised in cooling, and when they were drawn into thin plates the whole of the material became pervious to the electrolyte. plate of that kind six inches square would grow to eight inches square, and at one time we thought that that growth was a very fine thing: we thought that it really meant that we were making the plate more and more active, and that we were getting more and more useful material; but recent experience has led me to believe that that idea was wrong, and that as more active material was obtained continuity decreased, and that the greater part of heavily grown plates became useless. The best plates that I have known have been those that have grown least, and very magnificent results both of heavy discharges and great capacity have come from plates which, after having been formed for a year or a year and a half, have not grown more than from 6 inches square to 64 inches square: and this is very comforting to us, because it is evident that if a plate grows rapidly it loses mechanical strength, and is quite unfit for rough work at all, such as driving tramcars, and things of that sort; whereas it is proved that plates will get sufficient formation without any inordinate growth, without stretching the fine filaments of lead Mr. which join the whole fabric together to such an extent that there Crompton. is no longer any electrical continuity. Mr. Evershed. The Mr. S. EVERSHED: Mr. Swinburne's paper gives me a convenient opportunity of bringing before the Society a rather curious phenomenon which I observed about two years since, when working with small secondary cells. I had been forming a set of small Planté cells, and on one occasion, on cutting off the charging current, I noticed a rush of large bubbles to the surface from the whole of the cells simultaneously. Of course I thought I had shaken the cells, and I put on a very small current, and on carefully breaking the circuit (so as not to shake the cells), and observing the cells at the same time, I saw the large bubbles which had formed on the anodes rush to the surface instantly. I was able to repeat the experiment several times, and as I was working with Mr. Swinburne, I called his attention to it. We did not at the time go into the theory of the thing, and it has been put on one side. Quite recently I have made a rough experiment to ascertain, if possible, the cause of the rising of the bubbles. I had an idea that the surface-tension of gas bubbles might be diminished under the electrical action of the cell, and that, if I could collect a large bubble the surface of which could be easily altered on starting or stopping of the current, I should observe some alteration in its shape. However, nothing of the kind occurred, although I varied the conditions of current density, etc., as far as possible: neither oxygen nor hydrogen bubbles seemed to alter in shape in the least. I should be very glad to hear if some one else has observed this phenomenon, because, as far as my rough experiments have gone, I have not even been able to reproduce the conditions which evidently obtained in my experiments two years ago. The PRESIDENT: The subject which we are discussing to-night is one of great importance: it could not be exhaustively discussed, in fact, in two or three nights, but I have three more speakers on the list who wish to be heard. There is also Professor Forbes' paper, which we hope to be able to hear, and therefore I must ask speakers to be as brief as possible, to give Mr. Swinburne time to reply. Walker. Mr. SYDNEY F. WALKER: I will only make a very few remarks, Mr. as the time is short. I think we all are very much indebted to Mr. Swinburne for what he has said, and also to Mr. Crompton for his remarks. It is quite as important for us to know what we cannot do as to know what we can do, as if we know all we cannot do there is not very much left; and the subject is a most difficult one, because the electro-chemical and electro-mechanical requirements are in opposition. If you are to have a large current capacity, a big charge that is to say, from a comparatively small battery, apparently you want a large quantity of active material, which must be in a certain spongy state; and practically it amounts to this, that when you have a perfect plate electro-chemically it is useless, because it will not hold together. That is, as far as I can gather, the question, and apparently the experiments that have gone forward, divide themselves distinctly into two kinds-those in which a plate is plugged with active material, and those in which the plate is formed. Those who have experimented with the kind in which the plate is formed, apparently have endeavoured to divide up the plate as much as possible into very thin laminations in hair lead, and in the form which Mr. Crompton has referred to; but apparently the result is that, when they have got their perfect form, it is useless, because it is so rotten, and requires a backing of some kind. I imagine that with those in which the plate is plugged (I have not had very much experience with them) there must be a very great risk of the material falling out, owing to the unequal bulk which it occupies. Assuming Mr. Swinburne's figures to be correct, if you plug a hole with peroxide of lead, and it expands or contracts, whichever way you take it, there is great risk of its falling out and short-circuiting, and so on. Therefore, as far as all that I can read, and can learn from experiments that I have made, the direction which we have to go in appears to be on Planté's old lines, only to make the cells big enough; but of course their size is limited when they have to be portable. There are many cases-country house lighting, private lighting, etc.-for which secondary cells are a practical necessity, and in which it will not matter how heavy the cells are; but for Mr. Professor portable work some sacrifice will have to be faced. Apparently you cannot have long life and high charge in a small weight and compass. One of the great, almost the greatest difficulty, so far as my experience goes, in the use of secondary cells is the uncertainty of individual cells: you never know exactly when a cell is going to break down, and it does not end with the loss of its own electro-motive force. It is not a dead horse, but it becomes a horse pulling against you: you have to work through its resistance, and the working current going through it, as Sir David Salomons has pointed out in his pamphlet, sets up an opposing electro-motive force, so that practically it takes two cells to neutralise it; and I think, until we can get over this, and we can have cells which will not be liable at uncertain times to break down in this way, we shall not be safe, if I may say so, in using secondary cells, except in special cases where there is skilled labour always at hand. Professor W. E. AYRTON: I have had very little to do with the formation of cells since the early days of the Faure accumulator, about 1881-82; although I have have a good deal of experience since in the use of secondary cells. Speaking as a user, I have found that cells which are sent out ready formed, such as those supplied by the Electrical Power Storage Company, are much more convenient for users than those which are sent out with directions telling the buyer how to form the cells, which takes several weeks. In the ready-formed cells of the Electrical Power Storage Company, the positive plate-the plate by which the current enters in charging, and by which the current leaves in discharging-has in its holes minium, Pb,O,, while litharge, or PbO, is used for the negative plate. The different way in which plates are made consists in using a different oxide of lead for the positive plate to what is used for the negative plate, and that, I believe, is one of the great recent improvements. In the early days of the Faure accumulator, minium was used for both positive and negative plates. Also the modern plates are formed separately, but we will not go into that. In the early days of the Faure accumulator we were under the impression that lead sulphate was the great bugbear, and was to be got rid of by Ayrton. using sulphuric acid. As far as I know, Dr. Frankland was the Professor first to show that the lead sulphate was the most important thing in the cell, and I understand from the best chemists that the action in the accumulator in charging is the breaking up of lead sulphate PbSO, into PbO, which is deposited on the positive plate, and Pb which is deposited on the negative plate, with a liberation of sulphuric acid, H2SO; while the action in discharging is the re-forming of the lead sulphate PbSO. If that is the action of charging and discharging, why do we go through this roundabout way of getting the lead sulphate when it is lead sulphate which is decomposed in charging by the liberation of sulphuric acid, and which is reproduced in discharging? Might it not be possible to accelerate the formation of an accumulator by putting a certain amount of lead sulphate in it to start with? Mr. BERNARD DRAKE: My experience has been mostly con- Mr. Drak fined to one form of cell, which I have endeavoured to render a commercial success, and I have had little time for experimenting with batteries on entirely different lines. Mr. Swinburne states that if lead and peroxide of lead are electrically connected, and any of the surface of the lead is exposed to the acid, that part of the surface is attacked, and a thin film of sulphate is formed, which protects the surface from further corrosion. This was the old idea, which I believe we were the first to disprove. If sulphate is allowed to collect, the grid will be soon destroyed throughout. The protecting coat is one of dense peroxide and not sulphate. The table of volumes occupied by lead in different forms is most instructive, and clearly bears out our statement made before the British Association, that the formation of sulphate was the main cause of buckling. It is clear that if the pure lead grid is converted into sulphate, an expansion takes place, and the plate must either " "grow' or buckle. The destruction of the flannel referred to might have been caused by the strong sulphuric acid formed during charge. The flannel would prevent this from mixing with the remainder of the electrolyte, and the flannel would therefore be destroyed. Probably, also, the cells would give a bad result, as we found that |