AND THE ABSORPTION SPECTRUM OF GOLD. 45 



After a good deal of persuasion I succeeded in inducing the manager of the 

 W. H. Kemp Company Mr. W. II. HAN'NA to try the experiment of beating into 

 leaf, as thin as could be had, a sample of fine gold which I sent him. This was 

 " proof gold" from the assay department of the United States Mint at Philadelphia, 

 and therefore of the highest attainable purity. The result was quite satisfactory for 

 the intended purpose, though it would not have been so in a commercial sense, there 

 being a good deal of waste, and many torn leaves and large holes. The microscopic 

 appearance of this pure gold-leaf is shown in fig. 4 (Plate 1). It is in general like 

 the commercial specimens, but the lines are bolder and more strongly defined a 

 consequence, as I think will be shown, of the greater softness of the pure metal. 



Study of these microscopic appearances, and comparison of them with each other 

 and with the micro-photographs of OSMOND, RoBEETS-AustEN, ARNOLD, ANDREWS 

 and others, did not seem to support the idea that the lines in question are due to 

 more or less distorted crystalline structure. In order to learn whether the lines are 

 to be referred to, and originate in, the process of gold-beating by which the leaves 

 have been produced, the attempt was made to obtain galvanically-deposited films of 

 something like the same thickness, so that these latter might be microscopically 

 examined by transmitted light. 



Pieces of thin rolled silver foil, much larger than would be needed for microscopical 

 examination only, were varnished on one side and then electrolytically coated with 



/ ' ti \J 



fine gold on the other, using a specially prepared pure cyanide solution and an anode 

 of fine gold. As there was no guide by which to determine in advance the thickness 

 of the gold film which would admit of being satisfactorily seen through, the current 

 was passed for various periods of time, producing films of several different thicknesses, 

 and, after the subsequent treatment, one or two were selected which gave the best 

 results. About a square centimetre cut from each piece of foil was well washed with 

 ether to free it from varnish, and was then cemented the gilded face downwards 

 upon a slide of .thin microscope cover glass by means of Canada balsam somewhat 

 diluted with ether. After time had been afforded for the balsam to harden, the silver 

 was dissolved oft' slowly by very dilute nitric acid, and the gold film was ready for 

 microscopic examination. Fig. 5 shows the appearance presented, the amplification 

 and distance from eye-piece to camera plate being the same as for fig. 1 and for all 

 the other microscopic illustrations of this paper. It is evident that the mottled 

 structure of this film, showing varying thickness, is unaccompanied by the ramifica- 

 tions of well defined black lines to be seen in beaten gold-leaf. No attention should 

 be given to the two large bars of shadow crossing each other at right angles in this 

 photograph ; they are due to the shadow of a part of the window sash having been 

 inadvertently allowed to fall on the illuminating mirror of the microscope. 



To test whether the black lines are really due to minute threads or wires of gold 

 with diameters considerably greater than the thickness of those parts of the leaf 

 which can be seen through, it was proposed to protect a piece of gold-leaf by placing 



