COLLECTIONS IN ECONOMIC GEOLOGY AND METALLURGY. 15 



Application of Gold. 



GrOLD LEAF. 



A single illustration of the application of gold is shown in the col- 

 lection llustratiug the manufacture of gold leaf from the works of 

 Hastings & Co., Philadelphia, Pennsylvania. This collection begins 

 with gold in sheets as thin as it is possible to roll it, and follows through 

 the various stages of reducing its thickness, by beating between skins 

 on a wooden block with a peculiar-shaped maul, until it is about 70V0 

 of an inch in thickness, which constitutes the ordinary gold leaf of com- 

 merce. The specimens are : 



(1) Ribbon of 23^ karat gold, rolled as thiu as possible betweea steel rollers. 

 (51106.) 



(2) Ribbon, cut into convenient size for beating. (51107.) 



(3) Foil, produced by beating No. 51107 for half an hour with a 15-pound hammer. 

 (51108.) 



(4) Foil, No. 51108, marked off into quarters. (51109.) 



(5) Foil, a quarter of No. 51109. (51110.) 



(6) Foil, obtained by beating No. 51110 for one hour with 12-pouiKl hammers. 

 (51111.) 



(7) Foil, No. 51111 marked off into quarters. (51112.) 



(8) Foil, a quarter of No. 51112. (51113.) 



(9) Foil, obtained by beating No. 51113 for five hours with 8-pound hammers. This 

 sxjecimen is inclosed in the skin used to inclose the foil during beating. (51114.) 



(10) Foil, commercial size of foil 3| inches square and Yihm of an inch thick. (51115.) 



(11) One dollar coin, showing sufficient gold to make 100 sheets of No. 51115. 

 •(51116.) 



IlilDOSMINE. 



This is a natural alloy of the rare metals iridium and osmium, con- 

 taining variable proportions of these metals, together with rhodium, 

 platinum, and ruthenium. It carries from 43 to 77 per cent, iridium, 

 and 17 to 48 per cent, osmium. 



It crystallizes in the hexagonal system, but crystals are rare. It is 

 generally found in flattened grains similar to gold dust, and associated 

 with gold and platinum. It varies in hardness from 6 to 7, and in spe- 

 cific gravity from 19.3 to 21.12, has a full metallic luster and tin- white 

 color, and is only slightly malleable. 



Considerable amounts are found in washing for gold, especially in 

 the beach sands of the Pacific coast. 



Iridosmine is remarkable for its infusibility and resistance to all ordi 

 nary solvents; all single acids and even aqua regia fail to dissolve it. 

 Iridosmine, as found, is used only for tipping the points of gold pens, 

 but considerable amounts are required for this purpose. The naturally 

 occurring material is carefully picked under a magnifying glass, and 

 all the grains of proper size and shape are saved and utilized. 



When iridosmine is sent to the mint with gold dust its removal causes 

 considerable trouble. The plan now followed is to add a large amount 



