19th Century: A Silver-Platinum Ratio

Ref

Following the age-old Gold-Silver Ratio, the Price of Platinum was frequently expressed as a ratio to Silver and/or Gold.  Comparing cited Platinum (and not ore) prices to London Bar Silver (see below), the ratio for refined ingot metals was never lower than 5:1 after 1867.

It appears the Platinum ratio was never below 4:1 after 1840, nor was it ever below 3.5:1 (1830-1).

1874: ~5.71/1 
1875: ~5.4/1
1876: ~6.02/1
1877: ~5.83/1
1878: ~6.06/1
1879: ~6.25/1
1880: ~5.96/1
1881: ~6.19/1
1882: ~6.67/1
1883: ~6.8/1
1884: ~7.05/1
1885: ~7.58/1

In an excellent historical summary, the US Platinum Price 1867-1904 is borrowed from Raynor's Johnson & Matthey invoices (erroneously transcribed by Bullsman in 1892):

Citation: The Journal of the Canadian Mining Institute, Vol. 8, By Canadian Mining Institute

1867 - 1907: Silver Fell -51%

1868: 1 Troy Ounce Silver = USD$ 1.33

1907: 1 Troy Ounce Silver = USD$ 0.65317 

1865 - 1904: Silver Fell -55.85% 

1865: 1 Troy Ounce Silver = USD$ 1.3384

1904: 1 Troy Ounce Silver = USD$ 0.5909

USD$ Silver Chart:

The Value Changes of Gold & Silver, as estimated in the Pound Sterling against a broad Commodity Basket.

Citation: Money and currency in relation to industry, prices and the rate of interest, By Joseph French Johnson

 Gold-Silver Ratio, as estimated in the late 19th Century.

Citation: The history of bimetallism in the U.S. 4th ed By James Laurence Laughlin, 1900