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THE ELECTROCHEMICAL EQUIVALENT OF SILVER.
13. The electrochemical equivalent of silver has been determined repeatedly by absolute measurements, i. e., by means of instruments which allow a calculation of the current in terms of the fundamental units of mass, length, and time. Among the earlier investigations only those of Rayleigh and Mrs. Sidgwick and of Fr. and W. Kohlrausch can be considered accurate. In order to express all measurements in terms of the same standard, the different values found have been reduced to those given by the porous-cup coulometer, and these are given in the last columns of the following table. Since in most cases the exact conditions of the experiments are unknown, these corrected values will simply give a general idea of the agreement between different observers.
As will be seen, Richards's and Van Dijk's corrections differ considerably. In deciding upon my own corrections I have taken the average of these two and those proposed by myself elsewhere.a
It was thought unnecessary to take into account the possible effect of included mother liquid.
From this list we see that the results obtained so far are not very satisfactory.
The most reliable experiments made in the United States, England, Germany, and the Netherlands lead to an average of 1.1178 mg for the electrochemical equivalent of silver, while the last two French determinations give a value of about 1 in 1,000 higher than this. Redeterminations in absolute measure with the use of a reliable form of coulometer are highly desirable.
14. The electrochemical equivalent of silver may also be expressed in terms of the electromotive force of a standard cell, i. e., by comparing the electromotive force of the cell with the potential difference produced by the current at the terminals of a known resistance. The electrochemical equivalent will depend upon the value chosen for the electromotive force of the standard cell. The legalized value for the Clark cell is 1.434 volts. But this is probably too high. In Germany the electromotive force of the Clark cell is derived from silver-coulometric measurements, and the Reichsanstalt has chosen as the working value 1.4328 volts at 15° C. In the following table the electrochemical equivalent of silver is calculated as well for an electromotive force =1.434 as for 1.433 volts.
a Transactions of the International Electrical Congress, St. Louis, II, p. 104, 1905.
a Mascart: J. de Phys., 2, p. 100, 1882, and 3, p. 283, 1884.
a Carhart:, Am. Jour. Sci., 28, p. 374; 1884.
In the case of Perot and Fabry, who used a Clark cell at 0° C. and found its electromotive force to be 1.4522 volts, using 1.118 mg as the electrochemical equivalent, the difference of 0.0164 volt given by the Reichsanstalt has been used to reduce to 15° C., instead of the ratio given by them. The latter would give 1.1180 mg in the first column and corresponding values in the others and make the agreement with the earlier experiments a very close one.
The large differences between the earlier and the more recent comparisons can hardly be due to the silver coulometer alone. Doubtless the Clark cell comes in for its share.
Wolff and Carhart and Hulett have lately discovered an electrolytic method of preparing mercurous sulphate. Cadmium standard cells, in which this substance is used, show, according to preliminary reports, an excellent agreement among themselves, and no variation in their electromotive force in course of time as far as can be ascertained during a relatively short period.
With the improvement of our standard of electromotive force and the construction of a reliable silver coulometer, a wide and interesting field for research has been opened, and it is to be expected that the new determination of the volt and the ampere, which are in progress in the different countries, will show an agreement considerably better than the older ones.
HISTORY OF THE STANDARD WEIGHTS AND MEASURES
OF THE UNITED STATES.
By Louis A. FISCHER.
The subject of weights and measures is one of such great interest and importance and is attracting so much attention in this country and in England at the present time that a short account of the steps taken to secure uniformity in the United States is deemed an appropriate subject to bring to the attention of this convention.
The attention of the United States Government has long been directed toward securing uniformity in this country, and in the effort to secure international agreement in weights and measures it has always shown the greatest interest. The history of the original Confederation of States and of the constitutional government of the United States is full of evidences of the perplexities arising from the diversity of weights and measures throughout their jurisdiction and of the desirability of a uniform system.
The weights and measures in common use in this country at the time of the American Revolution were all of English origin and were in use in England at that period. The principal units were the yard, the avoirdupois pound, the gallon, and the bushel. More or less authentic copies of the English standards of the denominations mentioned had been brought over from time to time and adopted by the different colonies. Divergencies in these weights and measures were, however, quite common, due no doubt to the fact that the system of weights and measures of England was not itself well established, and hence the copies brought to this country were often adjusted to different standards.
That this condition was recognized very early is made evident by the Articles of Confederation which contained the following clause: “The
a An address delivered before the First Annual Meeting of the Sealers of Weights and Measures of the United States at the Bureau of Standards, Washington, D. C., 1905.
United States in Congress assembled shall also have the sole and exclusive right and power of regulating the alloy and value of coin struck by their own authority, or by that of the respective States-fixing the standard of weights and measures throughout the United States." This power was transferred to Congress by the Constitution of the United States in article 1, section 8, the language being as follows: “The Congress shall have Power . . . To coin Money, regulate the Value thereof, and of foreign Coin, and fix the Standard of Weights and Measures;”.
While Congress was not slow to take action in regard to coinage, it seems not to have been inclined to come to a decision in regard to weights and measures, though apparently willing enough to consider the subject. Washington, in his first annual message to Congress, January, 1790,a stated that “uniformity in the currency, weights, and measures of the United States is an object of great importance, and will, I am persuaded, be duly attended to.” In accordance with Washington's suggestion, the matter was referred to a select committee of the House of Representatives with instructions to prepare a bill, and it was also ordered that the matter be referred to the Secretary of State to prepare and report to the House a proper plan for establishing uniformity in the weights and measures. Jefferson was then Secretary of State, and in response to the above request made a report, in which he proposed two distinct plans. The first was substantially to define and render uniform and stable the existing system to reduce the dry and liquid measures to corresponding capacities by establishing a single gallon of 270 cubic inches and a bushel of eight gallons, or 2,160 cubic inches
The second plan was “to reduce every branch to the same decimal ratio already established for coin, and thus bring the calculations of the principal affairs of life within the arithmetic of every man who can multiply and divide plaid numbers."
No action was taken, however, by the House and in his second message to Congress, on December 8, 1790, Washington again called the attention of that body to the importance of the subject. A few days later the House ordered that the report of Jefferson, referred to above, be communicated to the Senate. On March 1, 1791, the Senate committee to which the matter had been referred reported that it would not be eligible to make a change in the weights and measures, as a
a Messages and Papers of the Presidents, 1, p. 66.