[LM111335] Essay, February 4th, 1889


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[LM111335] Essay, February 4th, 1889

Editor's Notes

On some recent improvements in the preparation of the plates and solution for the Edison electrolytic meter.##[A latin moto]##"I reckon none but the bright hours" is a proverb that for some two thousand years has been regarded as the exclusive possession of the sundial, the same old words p---ing again into notice from the gnomon on the crumbling portal of some ancient roman resin, some medeival picture, or even from the bases of some garden dial basking in the sunlight of our own time: yet it would seem that the phrase quite so aptly deserves to be shared by the modern electric light meter, and no electric light meter has yet made its appearance that more simply more ine--p--si--ty or more truthfully claims its ----- to the motto than the Edison Electrolytic meter with which we are all so familiar.##It is not however with its faithful service in the past as six years practical experiences with the Edison meter has lately altered that we here propose to discuss, not will the recapitulation of its merits be now our concern. Our attention will rather be directed to certain defects its possesses, depots which have often been considered as inherent ones, not akcnolwedge ------ its friends and certianly magnified by its enemies, but which we have good to##[one line or so cut off in the photo of this document]##It is evident that the meter cannot fail to register correctly when supplied with pure chemicals if the combined resistance of the bottle and spool remains uniforms. It is known that this condition is practically fulfilled when the meter is steadily worked at fair l--ds, but that there is a tendency for the resistance of the bottle, to rise unduly as the load diminishes or the working intervals become more rare, this diminishing the current in the bottle circuit and causing the record to fall short, in fact under practrically condition the underindication may amount to 10% while under extremely unfavorable conditions seldom or never actually realised the error might reach 25%.##A series of experiments for the investigation of this kind other prints connected with the meter have recently been carrie don for the Electric Light Co by Mr Edison at his laboratory in Orange N.J. and it was found as anticipated that this undue resistance at light and discontinuous load was produced by the badly conducting film on the immersed plot surfaces, produced by oxides *, the effect being almost entirely confined to the periods of inactivity and being counteracted by the operation of the meters so that while the effect of rest is to increase##[at least one line cut off from the photo of this document]##[page 169]##This superficial layers of oxide which as he knew tarnishes the plates and adds in their weight is considered not to be due to any direct combination of zinc with oxygen from the water for that would necessitate the decomposition of the water and the liberation of the dissociated hydrogen, a power it is generally acknowledged that zinc does not possess. The oxide is due to the oxide of the zinc with water and free oxygen an atom of the mutual combining with a molecule of the liquid and an atom of oxygen gas which under ordinary conditions is found ready for the purpose either dissolved in the water or occluded beneath the amalgamated surfaces of the metal.##The quantity of atmosphere oxygenthat water will hold in solution at normal pressure diminishes with the temperature being about six cubic inches per gallon at zero centigrade and about four cubic inches at 20 [degree symbol] C (--F). At boiling point it is only very slightly soluble but even prolonged boiling is said to be incapable of expelling it entirely. The amount of water contained by a No 4 meter bottle in ordinary use is about 15 cubic inches and when filled with tap water at 15 [degree symbol] C (60 [degree symbol] F) holds about one quarter of a cubic inch of atmospheric oxygen in solution.##In addition to this, the zinc plates themselves contain embedded beneath their surfaces a certain small amount of oxygen and in fact all substances seem to possess ab-----tive power in a greater or less degree. Thus while glass is said to only retain the thirty thousandth part of a cubic inch of gas per square inch of surface, charcoal will hole ninety time its own --lt of ammonia, and the absorbtive power of a carbon lamp filement is evidenced by the necessity to raising it to incandescence during the period of exhaustion in order to expel th gas by heat. It is probable that the amalgamated surface of the meter zinc contain in this way quite an appreciable quantity of con---- oxygen.##[page 170]##That the tarnishing of the plates is due to the existence of this fuse oxygen in the presence of water is shown by the fact that when steps are taken to exp--- it from both plates and solution by heat the plates will either not tarnish at all durin the usual period of one month or if the solution be quite neutral they will tarnish but only very slightly and slowly. A $4 bottle made up with plates and solution freed from oxygen in this way at the Edison Laboratory and left inactive has the lu---- on its plates as bright at the date of writing this paper as when first amalgamated and [immersed?] three months ago, and its resistance is no higher than it was at that time, while another bottle made up at this same time in the usual manner tarnished within 49 hours.##Different qualities of water used for preparing the solution contain very different quantities of dissolved gases. For example freshly distilled water naturally contains least of all as its taste indicates owing to its recent [coindeneation?] from paper at a high temperature when its absorbtive power was very small. It is now practically known that meter solution made up from freshly distilled water will reduce the amount of monthly oxidation weight from 50 to 78 % with a correspondingly reduced tendency to registration --- so that the allowance for oxidation on as no. 4 plate in such solution would be 25 to 50 milligrammes only.##On the other hand water which has been freely exposed to air at low temperature such as most city or rain water especially in cold weather is comparatively rich in distilled oxygen. It is curious too that although the effect of freezing is said to expel all the dissolved gases from water so that in in itself contains none, yet the numberless little bubbles and fissure visible in the substance of -- are cells of imprisone gas forced out of solution by regulation##[page 171]##On ----lting this expelled gas seems to be reabsorbed for ice water and snow water are notoriously rich in oxygen. Hence the use of ice for the preparation of meter solution while it generally ---- a ---- liquid at the same time introduce a marked tendency to oxidation, to rise of resistance during inactive periods, and to underindicatoin of the meter.##After the trial of a number of method- per the expulsion of the gas the best plan seems to be practically as follows##Make up the solution in the usual way to the right density. Then heat so much of it as can be conveniently managed at one time in a ---- of porcelain at agate ware over a spirit lamp or Bureau burner. If the solution be made from distilled water that has had access to air, just raising to boiling point is sufficient, but if prepared from -- it shall be allowed to boil for half an hour. On cooking it should then be poured into a closed vessel, bottle ------, at carbo-, as soon as the temperature permit, and when it has quite cooled down, the density can be corrected for the loss of water in vapor during the heating process by adding some water that has been separately boiled. The solution should then be kept closed up out of free access to the air until needed. Solution prepared from distilled water freshly made or kept in closed vessels, will only contain such oxygen as may be introduced by the --- salt and will probably not need further treatment.##If under existing conditions the boiling process cannot be conveniently carried out on a seale sufficiently large to meet the demands of a station, then it would always be advisable to process distilled water for m-ta purposes.##[page 172]##----- is prepared to furnish from his ----- meter solution properly treated in sealed carbo-s that no boiling would be required at the st---- before use after arrival.##It is not yet known how many times the solution can be used over again in practice before boil--- again becomes necessary. Much will probably depend upon the amount of air left in - bottle which should be fitted as completely [as?] possible the agitation they must undergo in ----ment and removal etc.##The best treatment for the plates has been found to set a number of them in a shallow agate ware dish like a frying pan, to pour ---- till they are nearly covered and then to heat the dish over a burner to boiling point. This plate should then be withdrawn and immediately amalgamated while ---. If the mercury can itself be warmed it will be all the better. They should then be freed from [excess?] of amalgam by [brush?] or ch---- ----- skin in the usual way while still warm. Especial care should be paid to the removal of amalgam from the coupling holes as the amalgam formed at the high temperature is much more vi--id and consistent then when formed in the usual way and offers greater reisstance to expulsion by the brush. The plates may then be set to cool and though no doubt it is better to weigh and immense then as soon as possible no harm has been found to result from having then in air for two or three days before use.##After treatment in this way it is found that if the solution be quite neutral is if it contains no trace of sulphuric acid that the plates will slowly tarnish, the effect being simply to bring about oxidationmuch more gradually, the gains in weight at the end of a month amounting in a 4##[page 173]##plate to perhaps 10 milligrammes, but if the solution contain a very small quantity of free sulphuric acid say 1 part in 10,000 or 0.01 % this quantity which would have no appreciable effect on plates under ordinary treatment will in this case combine with the zinc forming sulphate of zinc and liberating hydrogen. The result will be a slight loss of weight instead of gain in the plates at the end of the month but their lustre will be maintained and the bottle resistance will not rise unduly. If the amount of free acid much exceed this above proportion this action will be precipitated hydrogen gas will be cooled on the surface of the plates and the los of weight will be proportionally augmented. If is therefore necessary to ensure either neutrality or only a very mild degree of acidity in the solution.##If then the solution be of proper purity and either prepared from distilled water or boiled, and if the plates be amalgamated hot, these will be every reason to expect an increased degree of accuracy in the registration of the meter even under the lightest and most intermittent loads.
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Thomas A. Edison Papers, School of Arts and Sciences, Rutgers University
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