II. On the Structure of Gold- Leaf, and the Absorption Spectrum of Gold. 



By J. W. MALLET, F.R.S., Professor of Chemistry in the University 



of Virginia. 



Received May 22, Read June 11, 1003. 



[PLATE 1.] 



GoLD-leaf, as seen under the microscope by transmitted light, presents a remarkable 

 appearance which seems to have been hitherto either not at all or only slightly 

 noticed. The colour of the transmitted light is bluish-green, unless silver in 

 considerable proportion be alloyed with the gold; in this latter case the colour is 

 purplish-blue. The amount of light transmitted is, as might he expected, not uniform, 

 the thickness of the gold film varying within very small areas of the surface. All 

 this is well known to anyone who has ever looked through a bit of the leaf. 



But, in addition, numerous black lines are visible under verv moderate amplification, 

 ramifying irregularly over the surface, here and there showing some tendency to 

 parallelism, but for the most part running into each other in the most irregular way. 

 Fig. 1* illustrates this ; it is a microscopic photograph of ordinary commercial gold- 

 leaf, taken with an amplification of 75 diameters, and a distance from the eye-piece to 

 the camera plate of 378 millims. 



In FARADAY'S Bakerian lecture, read before the Royal Society on February 5, 1857, 

 on the " Experimental Relations of Gold (and other metals) to Light," t there occur 

 two or three sentences which prove that this peciiliar appearance did not escape his 

 keen observation. For example, he says " when the thicker parts of the leaf were 

 examined they seemed to be accumulated plications of the gold, the leaf appearing as 

 a most irregular and crumpled object, with dark veins running across both the thicker 

 and thinner parts, and from one to the other." Again, referring to specimens of gold- 

 leaf which had been heated in oil, he says " it will be seen that it is the thicker folds 

 and parts of the mottled mass that retain the original state longest." And again he 

 remarks, " there is a little difficulty in admitting that such an irregular corrugated 

 film as gold-leaf appears to be, can possess any general compression in one direction 



* All of the microscopic photographs referred to in this paper have been presented to the Royal Society, 

 but only Nos. 4, 6, and 8 have been reproduced for publication, 

 t 'Phil. Trans.,' 1857, pp. 145-181. 

 (360.) G 2 29.1.04 



