Napoleon - The Common Ancestor for U.S. Silver (Barber, Mercury Dimes, etc.) and LMU Silver Coins

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The U.S. silver dimes that we are all familiar with are 2.5 grams (the Seated Liberty 1873-1874 and 1875-1891, Barber 1892-1906, Mercury 1916-1945, and Roosevelt 1946-1964). This is an unexpected size the U.S. has famously never jumped on board the metric bandwagon. So what's the deal?

NAPOLEON: THE ANCESTOR OF U.S. SILVER

The French system was formalized by Napoleon such that 1 franc was 5 grams silver at 0.9 fine (here). Thus, a 1/2 franc = 2.5 grams at 0.9 fine. In 1873, U.S. silver began to mirror French coins at a 1:5 ratio. U.S. dimes (10 cents) have the same weight, fineness, and silver content as the Napoleon III 50 centimes and earlier French coinage such as the Napoleon I 1/2 franc.

The U.S. Coinage Act of 1873 (here) set the new weights of U.S. subsidiary (<$1) coinage in terms of grams. The change in U.S. silver coinage was small (the weight of the dime was increased from 2.49 grams to 2.5 grams), but they were intentional to match the French system. The 1873 Act does not state this expressly, but the U.S. Comptroller of the Currency (here) explains that the act introduces:

a metric system of coinage suggesting the issue of a subsidiary silver coinage consisting of two half dollars constituting in weight and fineness an exact equivalent to the French five-franc piece, and a quarter dollar and dime with proportionate weight and fineness, which proposition was finally adopted.

At 5 grams, the short-lived U.S. 20 cent piece was equivalent to one franc. The U.S. quarter and half-dollar used the same ratio, but do not have an equivalent in the French system due to the 1:5 ratio. At 6.25 grams, one U.S. quarter (Seated Liberty, Barber, Washington) is equal to 1.25 francs and at 12.5 grams the half-dollar (Seated Liberty, Barber, Walking Liberty, Franklin, and 1964 Kennedy) are equal to 2.5 francs.**

Due to the 1:5 ratio for denominations (a story for another time), U.S. denominations do not reflect rounded weights like the French coins (2 francs - 10 grams, 1 franc - 5 grams) That is one reason why the French/metric connection of U.S. silver coins is overlooked.

WHY DID THE U.S. ADOPT FRENCH STANDARDS?

The 1860s-1870s were a period of international cooperation on monetary issues. U.S. adopt French monetary standards occurred shortly after the U.S. expressed interest in joining the Latin Monetary Union ("LMU") around 1867 (further info here). The LMU was formed in 1865 as monetary system of standardized coinage matching French coinage as established by Napoleon. There was only a few formal members, but LMU-type coinage was adopted by more than 60 countries.

The U.S. transition was also small and was not disruptive. Following changes in the 1850s (discussed below), U.S. silver was already very close to the French system. However, by the time of the Coinage Act of 1873 France had changing its subsidiary silver coins (<$1) from 0.9 fine to 0.835 fine in 1864 (an adjustment intended to compromise with countries and to keep smaller coins in circulation). So U.S. silver is a little different than French coinage of the same year, but they have a common ancestor -- the French monetary law of 1803 by Napoleon I. A 1960 Roosevelt dime is identical to a 1808 Napoleon 1/2 franc: 2.5 grams, 0.9 fine, 18mm.

As an aside, due to the French influence (in Europe and North Africa) and French/U.S. influence in the Americas, this 2.5 gram coin size was ultimately minted in over 70 countries across over 150 years (listed here). This makes it one of the most widely minted coin sizes in history.

THE SILVER DOLLAR EXCEPTION

The silver dollar (the seated liberty and later Morgan dollar) did not follow the metric trend. At 26.73g (0.9 fine), the Morgan dollar outweighed the French 5-franc piece (25g, 0.9 fine). Why?

The initial reason was simple. The U.S. Coinage act of 1873, which had defined subsidary silver in French metric terms, discontinued the silver dollar entirely. This divergence between the silver dollar and subsidiary coinage (<$1) traces back to the U.S. Coinage Act of 1853, which debased silver coinage by 8%, except for the silver dollar. Following this debasement, a U.S. silver dollar contained proportionately more silver than the subsidiary coinage. This is one reason the silver dollar was not in circulation by 1873.

Why was U.S. subsdiary silver debased? In the 1850s the California gold rush made silver more valuable, relative to gold, and the silver coinage used in everyday transactions became scarce. By reducing their silver content the U.S. sought to keep these coins in circulation (here). So why was the dollar denomination exempted from this debasement? A PCGS article explains that the silver dollar was largely out of use and unintentionally omitted. As of the 1853 act, mintage of the silver dollar was indeed low, but I find the "omission" explanation a bit unsatisfactory. Until 1873 silver dollar continued to be minted at its old weight. In 1873, when the silver dollar was excluded entirely, a trade dollar was introduced, which was even larger (27.22 grams rather than 26.73 grams), further diverging from subsidiary silver. A trade dollar had nearly 11 dimes worth of silver!

Both France and the U.S. had the same quirk: large coins contained more silver than smaller ones. France accomplished this by reducing the fineness of smaller coins while the U.S. reduced the weight of small coins but kept the dollar heavy.

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TDLR: In 1873, the U.S. adjusted the size of silver (dimes, quarters, half dollars) to mirror the French standard at a 1:5 ratio. Napoleon I established a metric standard coinage system (1 francs = 5 grams at 0.9 fine) in 1803. Thus, U.S. silver dime is the same weight, fineness, and diameter as a 50 French centimes (half franc) minted under Napoleon: 2.5 grams of 0.9 fine.

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* This 1 to 5 ratio was used throughout the Americas.

** The 2.5 francs was used by Belgium, but not France. Due to the 1:5 ratio in the Americas (2.5 francs = 50 cents local), there are 50 cent coins in Bolivia, Panama, and other countries, that match U.S. half-dollars.