[LM111256] Test Report, December 1888


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[LM111256] Test Report, December 1888

Editor's Notes

.####[page 143]####Section III####Suggested -----ments --able of being made in [future?], ------- meters in accordance with results of this entire investigation.####(1) Calibration.####It is submitted that the shunts and spools should be calibrated and fixed in terms of the legal ohm and not as at present in terms of the B.A. ohm.####This is not in any case a matter of much importance since it is the ratio between the meter circuits and ---- their absolute unless that effects their accuracy, and all meters are presumably repaired when necessary by the meters. Still the suggestion offers itself on the ground of uniformity in the electric light system which universally adopts the legal ohm in its operations.####(3) Platinoid Shunts####It is suggested that platinoid should replace german silver in the use of shunts, the reason being that while the coefficient of temperature variation in german silver is 0.044% per [degree symbol] C it is only 0.021 % per [degree symbol] C in platinoid, and consequently an equal variation of temperature will only produce half the usual alteration in resistance.####The platinoit metal supplied to the Edison laboratory by the S---vill Manufacturing Co of Waterbury Conn. has been found by several trials to have a specific resistance of 40 [mier ohms?] and a temp: --ff of 0.021%####The permanence in the resistance of a strip some 15 long and of approximately the same####[page 144]####breadth and thickness --- that in a No 4 Meter shunt was ---- by measuring its resistance ---- when ------- at its extremities into two clips and those operating it ---- in the circuit of a No 8 Edison under absorbing from 5 to 20 40f. during working hours, the current being from 15 to over 150 amperes according to the ---- at the end of a fortnight the resistance of the strip agreed with the originals determination to 1/4th of one percent, and the metal was as bright as when first used. The figures are given in Appendix K####The introduction of platinoid is not a matter of great moment, as the present limit of temperature variation with german silver is as already stated put--- within 1% on each side of the normal, but if no disadvantage can be offered to the trial of platinoid it is well worthy of consideration.####The [anti?] abolition of duplicate bottle. The abolition of duplicate bottles is a subject that has already engaged the attention of the Standardizing Bureau. The treatment of the bottles will probably so far remove the tendency of the meter to underindicate, that the necessity for a duplicate bottle on the ---- of inaccuracy will disappear. It is submitted that under the form and treatment proposed the second bottle will be superfluous, and it was pointed out, at a late meeting of the Bureau, that the complaints of customers might as validly be met with the argument of a duplicate plate in the same bottle as of a duplicate bottle itself. This proposition if adopted would reduce space and labour.####[page 145]####The nominal resistance of shunt and ----.####It is suggested as a matter well worthy of consideration that the present ---- of the bottle circuits and shunt circuit be -----. This of course has no effect on the meter constant that has a very marked effect on the meter accuracy. It has already been pointed out that an increase of resistance in the bottles amounting to one ohms reduce the current passing during that time through the bottles by 9.1% and considering the tendency that may occasionally present itself towards hydration even in spite of treatment, there is a wide range open to underindication. By doubling the resistance of each circuit, the deduction of current for -- of extra resistance in the bottle would then be only half as much 2.5%.####The adoption of this stop means no more than to take the old type of meter with two bottle on each side of the [neutral?], each bottle with a separate shunt, to throw aside the duplicate bottle and place the remaining bottle in circuit with the two shunts and two spools together with a slight alteration in the spools). The drop of potential will then be no greater with the proposed meter then with the double shunt meter and the only difference in cost of construction will be in a little ---- spool wire.####The ratio of shunt and bottle circuits.####It is submitted that the advisability of altering the existing ratio between bottle and shunt circuits needs consideration, this being a matter that affects the meter-constant and is independent of the suggestion of double resistances last made.####The reason for this suggestion is that it ----tting seems --- generally take place in the bottles####[page 146]####when a current of 10 milliampere passes through it continuously for more than 40 hours. That is equivalent to a steady load of 50% full values in a No 4 meter. It is certainly [rare?] for such a [can?] to present itself practically, but it seems desirable that a meter should be able to sustain permanently a greater activity than 50% of full load.####This ----tting has been the subject of experiments given in Appendix - It seems to be almost independent of the -ensity of solution, but takes place more readily of at low temperature. The 'smut' itself prove by chemical analysis to be pure zinc with perhaps a little hydrate. It appears that when the rate of deposit on a given area exceeds a contains amount the molecules of zinc do not have time to arrange themselves in the crystalline form their mutual-- attraction desires, and consequently an amorphous condition of small density and coherence results. This smelt has evidently less resistance than the layers of liquid through which it projects, fo it ---tinences to build up more rapidly on the formations, but it certainly has a distinct resistance considerably in excess of pure metal since smelting will continue as long as any liquid space remains unfilled between the plates.####Although 10 milliamperes generally produces sm--t after 30 hours in -- -- 4 plates as above mentioned, current of 200 milliamperes can be ---- for 6 hour without appreciable smelting.####No means have yet been found by which this action can be reduced. The density of current is the only menas that can at present control it. consequently as it seems undeisrable to increase the size and are of the present plates, th question for consideration is whether the current flowing through the bottle should be reduced. The advantage to be gained being the lessened####[page 147]####liability to smelt, and the disadvantages being that each milligramme transferred in a month would represent a greater amount of current than at present and thus call for a proportionally greater degree of care in weighing.####If however it is considered inadvisable to allow the constant, it will be necessary to observe precaution in the disposition of meters and their nominal rating, so that at no time any be called upon to operate continuously on over 50% of their present full load duty, so that for example the present 20 amperes for a limite period continuously.####Should it be considered desirable to ins---- the capacity of these meters in the manner suggested then the question arises as to what amount of change should be mad ein the resistance ratio and meter constant. To this there can be only one answer, that the change should not exceed 20% as more than that degree of responsibility can hardly be thrown on the weighing in commercial practice. This therefore leads to another point viz that the reduction of current density by increase of resistance, in the bottle circuit to the amount of 20% will not only increase the accuracy of the meter so far as guarding against e----- bottle resistance is concerned, reducing the effect of an ----- ohm from 4.5% to 3.7%; but it would also result in causing cash milligramme of zinc transferred to represent one ampere hour of current and thus simplify the meter constant. It is true that this sompl---te of the constant would only come into consideration on establishing a station changing the subscriber's rates but on the other hand since the whole object of the meter is to record ampere hours, any####[page 148]####undetrimental means by which the indication of ampere hours could be obtained immediately from milligrammes without calculation could be hailed as an advantage.####The uses of two different classes of meters in any one station, each with its separate constant might give rise to confusion; but if the new meter with its changed constatnt were supplied to new stations as they formed, the difference in appearance and type would be ample means of distinction.####Plates.####The Bureau has already sanctioned and authorized the introduction of a modified form of the - plate for all meters of that and higher exp---ties. THe plate is - thicker than the original form but its areas remains unchanged. These paltes have been case in an ion mould at the Edison Laboratory from Bergmann rolled zinc from electrolysis zinc, both zinc, and alloy with mercury from 1 up to 5%. These mercury castings seem to require only one amalgamation at the ------ in order to work will thus ---ing the second and third amalgamations generally given to the existing form of plate; the metal seems well and if carefully handled oin casting some reliable and homogenous. Appendix M gives some measurements that show its density to be practically the same as Bergmann zinc if no mercury is used, so that there seems to be no danger to be apprehended from softness of material.####An important advantage is seemed by casting a tube of zinc [1/4?]'' long over the copper rod above the entrance of the latter in the plate proper. Appendix H give some measurements which hsow that when the junction between metal rod is submerged and the copper surface is not protected by varnish, local action produce loss of weight in the zinc.####
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Thomas A. Edison Papers, School of Arts and Sciences, Rutgers University
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