44 PKOFESSOE J, W. MALLET ON THE STEUCTUEE OF GOLD-LEAF, 



only." But FARADAY does not seem to have specially investigated the peculiarity in 

 question, or its cause, and, in view of the process by which gold is extended into 

 these thin films, the terms " plications " and " folds " which he uses must be understood 

 as referring to the appearance only of the leaf and not to its actual structure. 



The idea first suggested by the ramification and reticulation of black lines was that 

 they might depend in some way on the crystalline structure of the alloyed gold used 

 for making commercial gold-leaf, modified and distorted during the process of beating. 

 Hence specimens of gold-leaf variously alloyed were compared with each other. The 

 following samples were furnished me by the manufacturers, the W. H. Kemp Company, 

 of 165, Spring Street, New York, with a statement of their composition : 



A. Dark or red gold-leaf, made with an addition of 18 grains of copper to each 



Troy ounce (480 grains) of pure gold, or, more strictly, gold assaying about 

 998-999 fine. 



B. Gold-leaf of medium colour, made with an addition of 12 grains of copper and 



1 2 grains of silver to each Troy ounce of fine gold. 



c. Pale or light-coloured gold-leaf, made with an addition of G pennyweights 

 (144 grains) of silver to the Troy ounce of fine gold. 



Figs. 1, 2, and :] show the appearance of these three samples respectively under 

 the amplification already mentioned for No. 1, which represents the gold alloyed with 

 copper only, No. 2 that containing both copper and silver, and No. 3 that containing 

 silver only. The three exhibit some differences, but not much greater than are 

 presented by different samples of leaf of the same composition, and the general 

 character is evidently the same. In consequence of the small amount of light 

 transmitted by the leaf, exposures of the photographic plates for two or three minutes 

 were necessary, and changes in the state of the sky and character of the light during 

 this time prevent the photographs giving quite a correct idea ot the different degrees 

 of translucency of the specimens. Owing probably to slight shaking of the floor 

 affecting the position of the camera, the ramified lines do not appear quite as sharp 

 and Avell defined as when viewed directly through the eye-piece of the microscope. 



It was desirable to see whether the same appearance, if referable in any way to the 

 original molecular structure of the metal, would present itself in leaf beaten from 

 pure gold free from all alloy. On applying to two firms of gold-beaters one in 

 New York and the other in Philadelphia to make for me a small quantity of leaf 

 from fine gold, I was assured by both that it was impossible to beat pure gold thin 

 enough to be seen through. Dentists' gold foil could be had, but it is quite opaque. 

 The reasons assigned for the difficulty were the excessive tendency of the pure gold 

 to cohere, so that it could not be manipulated without different parts touching each 

 other and sticking together, and also the tendency of the pure metal to stick to the 

 " gold-beaters' skin " or animal membrane used to separate the leaves in beating. 



