UK, 1815 : Bollman's Coinage Idea

1814: 1 Troy Oz. platina (whols.) = £ 0.15 - 0.20 (USD$ 0.478 - 0.638)
1814: 1 Troy Oz. Platinum (retail?) = £ 1.25 - 1.75 (USD$ 3.99 - 5.58)

February, 1814:

Citation: Encyclopaedia Londinensis, or, Universal dictionary of arts ..., Vol. 15 (1817) p.480

1815: W.S. Jones Catalogue addendum, dated

Citation: An analysis of the principles of natural philosophy ; Matthew Young (Bishop of Clonfert), p.464

In an 1815 letter, Dr. Bollman's hypothetical $1 and $2.5 US coin are mentioned. An number of London bank tokens were coined.

The idea for Platinum coinage persisted in several nations: mules were even struck.

At the market-rate of £ 0.15, it would have been impossible for any nation to furnish The United Kingdom £ 200,000 or 41,460 kilograms of the metal, annually.

Citation: The domestic encyclopedia: or, A dictionary of facts and useful ..., Vol. 1 ; Anthony Willich, Thomas Cooper pp.498-500

US Mint Collection, 1815 mule: example of Bollman's coin, perhaps the $2.50 piece, referenced by John Quincy Adams.

The actual 1815 US Silver Half-Dollar weighed ~208 grains (13.48 grams) and the alloy (89.2% Ag and 10.8% Cu) should have an estimated specific gravity of 10.293. Assuming the specific gravity for pure Pt (21.51), a coin struck to the same dimensions at purity should have weighed 434 grains Troy, or .906 Troy Ounce.  

At 0.7181 Troy Ounce, the intrinsic value of the actual Platinum coin (@ "USD$ 3./oz" in 1813/4) was $2.1544

Weight: 344.7 Grains Troy
Specific gravity: 20.9
Diameter: 32.6 mm.
1860: 1 Troy Oz. Platinum (intrinsic) = USD$ 7.6588

Citation: A description of ancient and modern coins: in the cabinet collection at the United States Mint; Bureau of the Mint, James Ross Snowden (1860)

Liverpool: August 1815?  Dollar value drops by ~20% on ship rumor of abundant USD$ notes!