[D8830ACH], Letter from Harry Ward Leonard, Leonard and Izard to William J Jenks, October 16th, 1888


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[D8830ACH], Letter from Harry Ward Leonard, Leonard and Izard to William J Jenks, October 16th, 1888

Editor's Notes

"Yours of the 28th ulto. Relative to meters at hand. I am very much pleased to learn that Mr. Kennelly has taken up the meter work, and am confident that his investigation will result in very marked improvements in the meter. I think there is no device in the Edison business to-day which has received less intelligent study than the metere, and very poorly handed experiments were the basis of the present meter, and almost no work has been done upon it since it was first brought out, over six years ago. You were kind enough to ask me to make any suggestions relative to the work which might possibly lead to any improvement. For the past two years I have had little or nothing to do with any meters, but will make a few suggestions which are the result of my experience with them. It may be that amalgamated zinc plates in the present zinc sulphate solution are the best plates which could be used for a meter, but I think that this has not been clearly demonstrated by the original experimental work upon the meter. I presume that the several books containing notes upon the experiments upon meters have been preserved and are at hand in connection with the present work. If not, they certainly should be found, for they represent a great deal of work and contain a great many valuable pointers. But the great trouble with all the experimental work upon the meter was that every result obtained which was in the least difficult to interpret, was scrutiznized by the light obtained from supposing that the solution contained free acid. I did a great deal of experimental work upon the resistance of the meter bottle under varying conditions, but it was after the orginal work had been practically completed, and y results not agreeing with the previous work, very little attention was paid to them. It is just possible that they were recorded in the meter books at that time, but I doubt it. I have looked among my old papers to find some records of this character, but I find only one experiment upon the subject, which I send the notes of herewith. They are in a back portion of an old note book, which seems to have suffered considerably from some cause. Apparently from the notes I had two bottles set up with a standard ohm in series with them, and took deflections by means of a Thompson Reflector Galvanometer with a high resistance in series, off of the standard ohm, and then by arrangement of switches, took the deflection off of each of the bottles in order to get the resistance of each bottle by the comparison of its deflection with that of the standard ohm. The recorded readings show that the resistance of the bottles was quite variable. The readings recorded give the resistance of the meter bottles under various temperatures and under various currents in the bottle. It was almost impossible to get the same reading twice under apparently similar conditions. The resistance of the bottle was subject to wide changes even though great care was excercised in every way. The flow of the current made a very great difference in the density of the solution between the plates and the solution outside of the plates, as was evidenced by the action of light from a lamp passing through the meter bottle, the liquid in the center presenting a waivy appearnce due to the differences in density. By keeping the solution stirred up while making readings, a tolerably fair curve could be obtained, but this of course would not be a practical condition. The result of my work upon a meter, led me to believe that it was of the utmost importance to have the res. Of the meter bottle the least possible relative to the resistance with which it was in series, so that a wide change in resistance of the bottle itself would have but little effect upon the current passing throught it. The original meter curve from which the compensating spool was figured and which was made the basis of all figuring in meter practice, was made with the full current of 25 lamps passing through the shunt. Very few readings were made, and they were quite erractic. I enclose you herewith copy of this curve taken from an old note book of mine. Since the curve itself is wrong if the spool does compensate at present, it is the result of good luck rather management. I am not at all satisified that zinc is the best metal for the plates. The reason it was selected was, I believe, because it gave less congro electromotive force. I think that any plates used in the meter should be of elctrolatically deposited metal. It is well known that there is a difference of potential between rolled copper and electroletically deposited copper, and I believe there will be a difference of potential between any rolled or cast metal and the same metal electroletically deposited. Furthermore, it is practically impossible to procure zinc free from carbon, and while the carbon is no detriment to zinc for ordinary chemical purposes, it is the worst thing possible in the meter business. The oxide of zinc is a very objectionable feature, and the zinc oxidizes more readily than almost any metal which can be used. Silver would, in my opinion, be the best thing possible if the expense would not be too great. Copper would be preferable to zinc as regards oxidation, and because the metal would deposit in much better shape. I think it would be well to try amalgamated copper plates, and by all means, electroletically deposited copper. I do not think of any other points which would be of service to you, but if there are any other points which would be of service to you, but if there are any other points upon which I can render you any further assistance, I shall be only too happy to do so. I regret that I have not at hand the results of a great many experiments and curves illustrating the same, but in my various moves, they have by some means been lost, and I have not been able to find them as yet. In case they turn up, I shall be pleased to forward them to you." Yours very truly, H. Ward Leonard





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Thomas A. Edison Papers, School of Arts and Sciences, Rutgers University
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