Reference standards for mass and metal content of US coins

I was on the PCGS Coin Facts website to find the total mass of a Double Eagle. The mass is reported 33.40 grams. Knowing the mass of gold in a Double Eagle in terms of troy oz (i.e., 0.9675 troy oz), I calculated the total mass of a Double Eagle as 33.44 grams (using 4 significant figures). So, to verify my figures, I searched the web for the total mass of a Double Eagle. NGC's website stated the mass of a Double Eagle to be 34.4360 grams. Wikipedia states the mass as 34.4362 grams. Other sites give the mass as 34.44 grams or 34.436 grams.

These small deviations in the way these masses are reported may seem trivial, but, as a chemist, these numbers are screaming at me. Back in 1849, I highly doubt that the US mint was able to mass produce coins to one ten-thousandth of a gram. So it doesn't make sense to state the mass of a Double Eagle as 34.4360 grams or possibly even 34.436 grams. This variation in the way these masses are reported is not limited to Double Eagles; I have seen such discrepancies for almost all US coins.

So then, is there a reference source that states the mass of US coins in terms of how the US mint originally intended? For example, in the 1800's, it was common to measure mass in terms of ounces, troy ounces, grains, etc. Masses are now stated in the metric system. When converting from one system to another, there is always the chance of sacrificing a digit (if the number of significant figures is taken into account). If the mass of a Double Eagle was intended to 1.075 troy oz, then converting to the metric system should give 34.44 grams after rounding. It is tempting to write 34.436 grams to account for the error in rounding, however, stating the mass as 34.4362 grams makes no sense.

Sorry for the numerical analysis - I realize that it is not the most interesting topic. I am trying to find a source that states the mass of a coin with both the number of significant figures and the units as intended by the US mint at the time of production. I suspect that the US mint did not use the metric system back in the 1800's. This is probably the reason why there are so many variations in reporting the mass in grams. I see the same issue with the diameter of US coins as well.

 

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I am a chemist too, and those specs are way outside of precise. If you go to this wikipedia site you can see the original specs from the Coinage Act of 1792, then follow the other links for other denominations that were added or changed. Most of the weights were done in grains, which is the smallest unit they could measure with any precision. Hope that helps.

 

On a somewhat related note, I'd be interested in a site that states weight tolerances of (modern and historic) U.S. coins.

 

Anyone who would like a PDF table of US coin specifications from the U.S. Treasury, please PM with your email. It's free.

 

I got a copy of the Coin World Almanac GDJMSP suggested for $3.75 on ebay. It has all of the weights and tolerances and more. My new favorite book. Thanks for the suggestion!

 

I bought it also. Very resourceful. I got from Amazon $19.99
Thanks GDJMSP!

 

I sure will. Thanks.

BTW I could not find the specs for the Shield Nickel in the Coin World Almanac.

 

The specs are in my copies (76,77,78,84, and 1990 editions)
5.000 grams +/- .130 grams 77.162 grains +/- 2.00 grains diameter 20.50 mm composition 75 Cu, 25 Ni specific gravity 8.92

 

These are for the 1866-1873 issues. For 1873-1883 the specs are the same, but the tolerances are +/-0.194 g or 3.00 grains.

 

You are right, I just looked at the first listing (Because I knew the first listing would be the shield nickels) and didn't pay attention to the fact they loosened the tolerances in 1873.

 

OK, I see it now. Since the Shield Nickel has a slightly smaller diameter than the Nickels in subsequent series, it thought Shield Nickels would have a slightly smaller mass.
The one thing I find peculiar with the mass of Shield and Liberty Nickels is that the mass of these nickels are reported to exactly 5.000 grams or 77.162 grains. It seems like the mint switched over to the metric system during the last half the the 19th century. For example, up until 1873 the mass of the quarter was 96.000 grains or 6.221 grams. Then, the mass of the quarter was changed to 96.452 grains or 6.250 grams. The same is true for other denominations:

Dimes:
before 1873, mass = 38.400 grains or 2.488 grams
after 1873, mass = 38.581 or 2.500 grams

Twenty Cents:
after 1873 (starting 1875), mass = 77.162 grains or 5.000 grams

Quarters:
before 1873, mass = 96.000 grains or 6.221 grams
after 1873, mass =96.452 or 6.250 grams

Half Dollars:
before 1873, mass = 192.000 grains or 12.441 grams
after 1873, mass = 192.904 or 12.500 grams

Looking at the specs from the Coin World Almanac, the Shield Nickel is the first coin that the US Mint specified its weight in grams. I could not find additional information in the book, but from a quick search online I found the Metric Act of 1866:
The use of the metric system made legal (but not mandatory) in the United States by the (Kasson) Metric Act of 1866 (Public Law 39 - 183). This law also made it unlawful to refuse to trade or deal in metric quantities.

Since the Shield Nickel was first minted in 1886 (the same year of the Metric Act of 1866), I wonder if 1886 was the year the US Mint decided to switch from the English system to the Metric system.

 

Shield nickels are thicker than modern nickels. That's how they can have a smaller diameter yet the same mass.

 

That explains it. The conservation of mass. I have a Jefferson Nickel Dansco Album that had some extra ports at the end. So, I thought I would make a mini nickel type collection with the remaining ports. When I went to place a Shield nickel in a port, it would not fit snugly and rattled around. I though the album had a defect.

 

I haven't yet sprung for the Coin World Almanac. For those of you who have, does it give a source for the tolerances? The statutes I've found from the US government don't seem to provide them, and I'm wondering where they're codified...

 

It does for most. The only measurements that I found from "unofficial data" are some diameters in mm. The weights all appear from official data, but it doesn't refer to where that is found.

 

The 1947 table has been sent to all who requested it.

As for coin weights, the Mint and Congress were trying to make some aspect of coins in even metric units, or conform to Latin Monetary Union standards. For example, two post-1873 half dollars were exactly the same weight as one 5 Franc coin.

 

Got it. Thanks Roger!