4(5 PROFESSOR J. W. MALLET ON THE STRUCTURE OF GOLD-LEAF, 



it between two sheets of silver foil, roll the whole down to a fraction of the original 

 thickness, remove the silver by means of nitric acid, and see whether the lines in the 

 gold had been broadened out by flattening of the wire-like threads if present. A 

 rectangular piece of fine silver foil, '019 millim. thick, was folded in two across the 

 middle of its length, a piece of the " fine" gold-leaf which had been specially beaten 

 for me by the W. H. Kemp Company was spread out flat between the two folds of 

 silver, and then by the same firm the whole rolled down until the double thickness, 

 088 millim., had been reduced to 'OOG millim. Care was taken to introduce the 

 folded edge first between the rolls, so as to prevent as far as possible slipping of one 

 surface of foil upon the other. Examination with nitric acid of different parts of the 

 rolled-down foil showed that, although there had been no small tearing of the gold 

 and many holes had been produced in it, there were quite sufficient areas of it left in 

 a practically continuous state. Assuming that the gold had been rolled out pari 

 passu with the silver, each had been reduced to something like one-sixth or one- 

 seventh of the original thickness. 



A small piece of the foil in this condition was varnished on one side, and the other 

 side stripped of silver by very dilute nitric acid. A number of specimens were spoiled 

 at this stage, since the acid getting through any holes would attack the silver on the 

 other side and eat its way between the varnish and the gold film, which was so 

 exceedingly thin as not to bear any manipulation when unsupported. A few good 

 specimens, however, were secured. These were cleared of varnish by soaking in 

 ether, cemented by the gold face with diluted Canada balsam to slips of thin 

 microscope cover glass, and, after hardening of the balsam, the second film of silver 

 was gradually removed by very dilute nitric acid. Fig. (Plate 1), representing, 

 under the same amplification as in the other figures, the microscopic appearance of 

 one of these specimens of rolled-down pure gold-leaf, exhibits very distinctly the 

 flattening out of the minute metallic threads, favoured by the greater softness of the 

 gold than of the silver which enclosed it. 



As a further test of the black lines being due to minute wires or threads of gold, 

 specimens of the fine gold-leaf were thinned down by partial solution, in order to see 

 whether the lines would remain visible longer than the general surface of the leaf, 

 and the thicker lines longer than the more delicate. The solvent used was a |- per 

 cent, aqueous solution of potassium cyanide, to which had been added a little 

 hydrogen dioxide. The result is shown in fig. 7, and in fig. 8 (Plate 1), the former 

 of these representing a less, and the latter a more, advanced stage of the solvent 

 attack upon the leaf. The more gradual obliteration of the black lines than of the 

 rest of the surface is quite apparent. 



As it seemed to be established that the black lines under examination represent 

 microscopic threads or wires, and that these are developed in the gold during the 

 process of beating, it was natural to look for their possible origin in some correspond- 

 ing peculiarity of structure in the " gold-beaters' skin" or animal membrane between 



