Circa 1820, the similarity of Paris & London prices appears to indicate a stable market for refined Continental Platinum, but that period was ending.
In Pound Sterling, the Price of Gold stabilized in London to the 1800 level.
c.1821: 1 Troy Ounce Platinum (refined) ~ Fr 25. - 27. (£ 1.05 - 1.15)
c.1821: 1 Troy Oz. Platinum (scrap) = £ 0.6441 (USD$ 3.08)
The Russian assumed rate may have dated to 1821, prior to the cornered market or price-hike that mysteriously began in 1822. It is by no means certain Platinum traded wholesale at this rate in 1821/2.
c.1821: 1 Troy Oz. coined Platinum = 9.31 Silver руб = 37.24 Banco руб
~£ 1.55
Citation: The Gentleman's magazine, Volume 143 By John Nichols (1828) p.482