Platinum Foil, Weight by inch

1881: 10 cm² (1.55 Sq. In.) Platinum Foil = 11 - 13.2 Grams (169.75 - 203.70 Grains) 
∴ 1 Sq. In. = 109.5 - 131.4 Grains (7.1 - 8.51 Grams)  
∴ 0.516 - 0.619 mm thick (~B.P.G # 9, #10)

∴ 1 Ozt Platinum Foil (~B.P.G # 9, #10) = 3.65 - 4.383 Sq. In. (23.56 - 28.28 cm²)



Jacob R. Elkfeldt's estimation, circa 1870?

1 Cubic Inch of Gold weighing 10.167 Ozt = 316.231 Grams, so
1 Cubic Centimeter of Gold weighing 0.62 Ozt = 19.3 Grams

1 Cubic Inch of Silver weighing 5.532 Ozt = 172.061 Grams, so
1 Cubic Centimeter of Silver weighing 0.338 Ozt = 10.5 Grams

1 Cubic Inch of Platinum weighing 11.33 Ozt = 352.32 Grams, so
1 Cubic Centimeter of Platinum weighing 0.69 Ozt = 21.5 Grams





Queen's 1888 Catalogue (p.261) tabled the weight of Platinum Foil per square inch.

Thickness                            Weight
{"very thin" ~                          = 0.2581 grammes ....................(3.983 grains) }


.001 inch per sq. in. .............. = 0.400 grammes ....................(6.173 grains)
.0015 inch per sq. in. ............ = 0.525 grammes ....................(8.102 grains)
.002 inch per sq. in. .............. = 0.65 grammes ......................(10.03 grains)
.0025 inch per sq. in. ............ = 0.775 grammes ....................(11.96 grains)
.0031 inch per sq. in. ............ = 0.9 grammes ........................(13.89 grains)
.0035 inch per sq. in. ............ = 1.25 grammes ......................(19.29 grains)
.005 inch per sq. in. .............. = 1.8 grammes ........................(27.78 grains)  {B.P.G. #2}
.01 inch per sq. in. ................. = 3.5 grammes .......................(54.01 grains)  {B.P.G. #4}
.0179 inch per sq. in. ............. = 6.25 grammes ....................(96.45 grains)  {B.P.G. #8.5}
.0319 inch per sq. in. ........... = 11.15 grammes ....................(172.1 grains)   {B.P.G. #11.5}
.05 inch per sq. in. ............... = 17.5 grammes ......................(270.1 grains)   {B.P.G. #16}
.064 inch per sq. in. ........... = 22.4 grammes .......................(345.7 grains)   {B.P.G. #19}

The 18th Edition (n.d.) of Bullock & Crenshaw's Catalogue of Chemical, Physical, and Pharmaceutical Apparatus (c. 1888) lists Platinumware from Joaquim Bishop & Co. 

p. 121:
'687. Platinum Foil, .001, weight about 6 grains, per sq. in.'  (0.388 grams)
'688. Platinum Foil, .002, weight about 10 grains, per sq. in.' (0.648 grams)

An English textbook mentions very thin foil, actually tissue (0.0007?): 
10 cm2 = 1.55 sq. in @ ~0.4 Grams ; 1 sq. in = 0.2581 Grams

Citation: Exercises in practical chemistry: Elementary exercises, Vol. 1 Augustus G. Vernon-Harcourt, Henry G. Maddan (1869)
 
 
Assuming 'Thin Foil' a sheet 6 Sq.In. would weigh ~ 2.4 Grams; a 12" x 12" Sheet (144 Sq. In.) would weigh 57.60 Grams (1.852 Ozt)

Medium Foil "~1 Gram per Sq. In." =  13.58 Grains = 0.88 Gram
Medium Foil "~0.75 Gram per Sq. In." =  10.05 Grains = 0.65 Gram
Thin Foil "? Gram per Sq. In." =  6.173 Grains = 0.4 Gram

  




Eimer & Amend 1920:
 
Heavy Foil "1.0 Gram per Sq. In." = 15.43 Grains 
Medium Foil "0.75 Gram per Sq. In." =  11.57 Grains
Thin Foil "0.50 Gram per Sq. In." =  7.7 Grains 
Extra Thin Foil "0.25 Gram per Sq. In." = 3.86 Grains