394 



SCIENCE. 



[Vol. IV., No. 



in the cell, which is also attacked by the sulphuric 

 acid, with the formation of sulphate of lead. We 

 all know that sulphate of lead is a pretty fair insu- 

 lator. I think the action pointed out by Professor 

 Trowbridge in these cells, and the fact that there was 

 a little sulphate formed during the operation of the 

 cell ; the fact that the cell is restored after this pro- 

 longed charging, in which, of course, there must be a 

 great loss of energy ; and the fact that they ase restored 

 to their original condition, — would induce me to be- 

 lieve that it is nothing due to the impurity in the lead, 

 but rather is owing to the non-conducting film, which 

 discolors the plate. Besides that, with regard to the 

 short-circuiting, there is no short-circuiting in the 

 cell. I am quite satisfied from attendant circum- 

 stances and observations, and from experiments that 

 were made, that they saw no short-circuiting in the 

 cells. 



Before I leave this subject, I should like to say a 

 word or two with regard to the hope that Professor 

 Preece indulged in. I am glad that he has had such 

 an encouraging experience with regard to storage- 

 batteries. I am inclined to think he will be disap- 

 pointed in the hope expressed, of being able to charge 

 the cells on one day of the week, and then use 

 them during the rest of the week. A very simple 

 calculation would convince him, as well as the con- 

 ference, that such a plan is not practicable with his 

 present plant. Perhaps, if he increases his plant, he 

 may be able to do it : he cannot do it with what he 

 has on hand. If we take the figures as Professor 

 Preece has given them, of a candle from 2| watts of 

 energy, a 16-candle lamp would require 40 watts, 

 and that gives us an efficiency of about 18.6, — 16- 

 candle lamps per horse-power of candle-energy, 

 which I must say, in the first place, is good lighting. 

 40 watts, with 30 volts between its terminals, will 

 give us 31.3 amperes as the current to the lamp. 

 Now, if we suppose that Mr. Preece has, in using 10 

 lamps, for instance, — I do not know how many there 

 are in the plant used; we will say 10 lamps; put 

 the number small, because 10 lamps are enough for 

 ordinary use, — 10 lamps would require 13 amperes 

 to maintain them. 13 amperes for 3 hours would 

 be 39 ampere hours, we will call it, on an average 

 night, and, for seven nights in the week, would be 

 273 ampere hours. Now, we divide 273 by the effi- 

 ciency of the storage-batteries, — forty per cent, — 

 and we will get as the total number of ampere hours, 

 during which the battery must be charged, 6S2£. If 

 we divide that by the number of hours which the 

 charging would occupy, — twelve hours during the 

 day, — that will give us the time used in charging 



the storage-battery, to produce this result, and give 

 the current to the storage-battery of 56.9 amperes 

 and 42 volts; in other words, 52 amperes to .8 of 

 an ohm. The charging resistance of the battery 

 would certainly be greater than .8 of an ohm. I call 

 the charging resistance of the battery the difference 

 of tension between the terminals of the battery, 

 while the battery is being charged at the time *by the 

 current flowing in the circuit. That is what I desig- 

 nate by the term ' the charging resistance.' The 

 charging resistance I am sure, from my own experi- 

 ments, cannot be less than 2 ohms. Second, The 

 current of his machine would be very materially re- 

 duced. Besides that, admitting that he could get 

 this current of merely 57 amperes, which he requires 

 for charging the battery, the question is, How long 

 would his cell stand a current of that magnitude ? I 

 am inclined to think that a very few weeks' char- 

 ging with a current as great as that would very soon 

 use up his cells. 



Mr. Preece. — The assumption of the tempera- 

 ture he starts with there, is wrong; for I am only 

 using ten-candle lamps, and they absorb nine-tenths 

 of an ampere. If you go through with a calculation 

 on paper, you are sure to make a mistake. My cal- 

 culation shows that you can get two hundred am- 

 pere hours out of my battery: if so, I shall have 

 enough to last me a whole week; and the batteries, I 

 am quite sure, after they have been used a little time, 

 will give me that, and a margin to spare. I am quite 

 certain, notwithstanding those figures that I had the 

 pleasure of going over, that I shall be able to report, 

 that, from one day's charging, I have got my light 

 for a week. 



I will mention one fact, which I mentioned to you 

 this morning, that my gardener cut off the top of his 

 foot: at that time my battery was charged up Friday 

 morning. I had a dinner-party Friday night; and 

 whenever we have dinner-parties we make all the 

 show we can. On Saturday I had no dinner-party, 

 and I used my lamps as usual. On Sunday I used 

 my lights as usual. On Monday morning my man 

 cut off his toe. I had a dinner-party on Monday 

 night, and I did not know of the accident at all. I 

 got down just in time to dress for dinner. Without 

 saying a word to anybody, I trusted to my battery; 

 and I found my battery held on for the whole of that 

 night. I had, without any further attention to the 

 battery, sufficient light for two dinner-parties and 

 four days. And I think if we did that in an emer- 

 gency, with a little gentle care that could be given, 

 I shall not be far wrong in saying that I shall have 

 enough for a week's use. 



