1895.] ^'^ [DuBois. 



and burnished, was weiglied on a delicate assay balance. Sufficient gold 

 to produce a fine gold color was then deposited on it by means of the 

 battery ; the strip was then dried without rubbing, and reweighed, and 

 found to have gained ^V of ^ grain, thus showing that one grain of gold 

 can by this method be made to cover 200 square inches, as compared to 

 75 square inches by beating. 



" By calculation, based on the weight of a cubic inch of pure gold, the 

 thickness of the deposited film was ascertained to be -^johoo of an inch, 

 as against 3s?:z^o for the beaten film. 



"An examination under the microscope showed the film to be continu- 

 ous and not deposited in spots, the whole surface presenting the appear- 

 ance of pure gold. 



"Not being satisfied, however, with this proof, and desiring to examine 

 the film by transmitted light, Mr. Outerbridge has since tried several 

 methods for separating the film from the copper, and the following one 

 has proved entirely successful. 



" The gold plating was removed from one side of the copper strip, and 

 by immersing small pieces in weak nitric acid for several days the copper 

 was entirely dissolved, leaving the films of gold, intact, floating on the 

 surface of the liquid. These were collected on strips of glass, to which 

 they adhered on drying, and the image of one of them is here projected 

 on the screen by means of the gas microscope. 



"You will observe that it is entirely continuous, of the characteristic 

 bright green color, and very transparent, as is shown by placing this 

 slide of diatoms behind the film. By changing the position of the instru- 

 ment, and throwing the image of the film on the screen by means of 

 reflected light, as is here done, you will see its true gold color. 



"Mr. Outerbridge has continued his experiments, and, by the same 

 processes, has succeeded in producing continuous films, which he deter- 

 mined to be only the -z-.j-^hooij of an inch in thickness, or 10,584 times 

 thinner than an ordinary sheet of printing paper, or sixty times less than 

 a single undulation of green light. The weight of gold covering twenty 

 square inches is, in this case, j§§o of a grain ; one grain being sufficient 

 to cover nearly fcmr square feet of copper." 



In a lecture on "Matter," delivered at the International Electrical Ex- 

 hibition (Philadelphia), October 9, 1884, and subsequently printed in the 

 Journal of the FranUin Institute, September, 1885, Mr. Outerbridge him- 

 self made the following statement: 



"After a series of careful experiments. I have obtained, in this way, 

 sheets of gold, mounted on glass plates, which are not more than 40:^00^ 

 of a millimetre thick ; and I have some specimens to show you which I 

 have good reason to believe are not more than 5^00:^000 of a millimetre. 

 To give you an idea of this thickness, or, rather, thinness, I may say that 

 it is about ^ho V^^^ of a single wave-length of light. Such figures are not 

 haphazard guesses, but are based upon reliable and understandable data, 

 and are easily susceptible of verification. 



