October 17, 1884.] 



SCIENCE. 



393 



constant. To get a higher electromotive force, we 

 must produce bodies like permanganic, chloric, or 

 chromic acids, or peroxide of lead. It would seem, 

 during the electrolysis of water, peroxide of hydro- 

 gen is produced in very small quantity. The peroxide- 

 of-hydrogen reactions, which are so easily recognized 

 in an acid fluid which undergoes electrolysis, do not 

 belorjgMo it, hut come from a new acid, called per- 

 sulphuric acid. It seems that persulphuric acid is 

 the first product of the process, and that this per- 

 sulphuric acid is undoubtedly the agent which is 

 generally formed, and is often characterized as the 

 peroxide of hydrogen. That being the case, there- 

 fore, we have to consider cases where we can have a 

 reverse or converse reaction. The action of iodic 

 acid on hydriodic acid is a well-known case. There 

 is undoubtedly a considerable dissipation of energy 

 in the genesis of iodic acid, because it is not endo- 

 thermic, like chloric acid. The moment the hydriodic 

 acid is mixed with the iodic acid, free iodine and 

 water result. The original constituents appear again 

 without the complication of secondary reactions. It 

 is reactions of that kind that we require. It is to 

 the question of discovering reactions of that kind, 

 without dissipation of energy, that we shall in the 

 future look for the further advance of secondary bat- 

 teries. 



"With reference to what has been stated regarding 

 the economical working of the incandescent lamp, it 

 is quite clear that such favorable results can only 

 come from working with an incandescent filament at 

 a very high temperature. There is no reason why 

 the incandescent filament should not yield the same 

 efficiency as the arc. Some years ago I made a series 

 of experiments as to the increase of the amount of 

 luminous intensity with the temperature. Since that 

 time, experiments have been made by Violle and 

 other experimenters. All the results seem to prove 

 that as an average and fair way of representing the 

 facts, sufficient in the mean time for practical pur- 

 poses; that, above a temperature of 500° C, the mean 

 rate of increase of luminous intensity is as a sixth of 

 the power of the temperature. 



This law enables us to calculate the temperature of 

 the incandescent filament. There can be no doubt 

 of the explanation of the advantage of working at 

 higher temperatures. The greater the temperature of 

 the filament, the higher is the mean refrangibility 

 of the emitted light. If blue light is considered, 

 instead of the increase being as the sixth power of 

 the temperature, it moves up to the seventh. In case 

 of the violet rays, the rate of increase would move up 

 to the eighth power of the temperature, and con- 

 sequently the percentage of rays of high refrangi- 

 bility is greater at higher temperatures. I still think 

 that there are a great many points in connection with 

 the chemical constitution of the secondary battery 

 which require further investigation. 



Mr. Keith. — I would like to ask Professor Dewar 

 whether he has investigated, either theoretically or 

 practically, the decomposition and re-composition of 

 the sub-salts of lead, such as I considered some time 

 ago, and were the subject of discussion. I think he 



was not present at the time when I stated my own 

 experiments in that line. 



Mr. Dewar. — No, I regret to say that I have not. 



Mr. Keith. — Taking the solutions known as Gou- 

 lard's solutions, or sub-salts of lead, which are all 

 very soluble, the peroxide is readily formed and dis- 

 solved and re-dissolved in that solution, as my own 

 experiments have shown: so far, I have carried them 

 into practical effect only in laboratory experiments. 

 But I have found that all the electricity is returned 

 as electricity; but, of course, all the energy is not 

 returned. 



Mr. Dewar. — As I understand it, the eventual 

 action is admitted to be, that the peroxide of lead is 

 really produced from the sulphate. All I can say is, 

 that if you take and compress a block of sulphate 

 of lead on a platinum plate, and if it is electrolyzed 

 for hours, you will get a small deposit of peroxide of 

 lead. 



Mr. Keith. —I think the gentleman misunder- 

 stood my question. I want to state here, that, from 

 solutions of sub-acetate of lead, there is by electro- 

 lytic action deposited upon one pole the peroxide of 

 lead, and metallic lead is deposited on the other pole. 

 The reversal of the current reverses the operation: 

 the peroxide of lead enters the solution, and lead is 

 dissolved. There is a difference of potentials, say, 

 of 1.70 volts. 



Prof. George F. Barker. — I should like to point 

 out some of the defects in storage-batteries. I made 

 an experiment three years ago with secondary bat- 

 teries, and I called attention to these experiments in 

 the meeting of the American association at Mon- 

 treal. I believe that the same thing had been found 

 by Gladstone and Tribe; but I think that it did not 

 excel, although they said in their paper they had 

 seen it referred to. The cells to which I referred 

 were not Faure cells: they were cells of the Plante 

 type, of a peculiar construction. The lead plates 

 were of a peculiar form, but they were entirely sepa- 

 rated from each other. They were separated, also, by 

 pieces of wood to prevent the buckling. Now, with 

 regard to whether it was the impurities of the lead or 

 not, I am not inclined to agree with Mr. Keith on 

 that point. The lead, in the first place, was clean. 

 I have no doubt that the claim was a good one, and 

 that it was as absolutely pure as lead could be ob- 

 tained. Beyond that, they were so placed, that, if 

 the lead was not pure lead, any local action that 

 would take place in the cell on account of the im- 

 purities of the material would not affect the general 

 electromotive force of the cell: it would cause a 

 waste of the material, but no other effect, and would 

 not affect the resistance of the battery of this cell, 

 nor its electromotive force. 



I attribute this action to the formation of some 

 non-conducting film over the surface of the plates, 

 both the peroxidized plate and the metallic lead 

 plate. There is no doubt about it, both that the 

 metallic lead, in this particular form in which we find 

 it in the secondary battery, is attacked by sulphuric 

 acid, with the formation of sulphate of lead; and that 

 there is a chemical action and reduction of the lead 



