ON IRIDESCENT SILVEB. 
51 
microscope the surface, will be seen covered with delicate 
grooves, some thousands in an inch, formed by the sections of 
the concentric laminse, and this configuration gives rise to the 
glowing tints of the shell. The next step is to obtain an 
exact impression of this surface upon some good conductor of 
electricity. This we are enabled to do by means of fusible 
metal, if proper precautions are employed in taking the im- 
pression. I pursue exactly the same method as in taking the 
copy of a medal. After fusing the metal, I pour it upon oiled 
paper, and when the air bubbles cease to rise through the 
metal the oxide is skimmed from its surface with a card, and 
as soon as it presents the appearance of a perfect mirror the 
shell is forced down upon it by a sudden pressure. When the 
metal has cooled I remove it from the shell, and having ascer- 
tained the accuracy of the impression, immediately plunge it, 
before any change of the surface can occur, into the silver 
solution, thereby completing the circuit between the poles of 
the battery. In a few moments the surface of the metal is 
frosted with silver, and the configuration of the shell exactly 
copied. A sheet of silver, of sufficient thickness to be easily 
removed with a pen-knife, will be deposited in the course of 
five or six hours under favourable circumstances. The battery 
I have employed consists of two plates of amalgamated zinc 
and one of platinized silver, six inches by eight. The working 
mixture is sulphuric acid and water, the strength varying with 
the temperature, and the amount of work to be performed. 
I have found a wine-glass of acid to three quarts of well-water, 
at the temperature acquired by standing a few hours in a room 
at 70° Fah., to answer very well, when the surface to be 
plated did not exceed lh square inches. The silver solution 
is made by dissolving cyanide of potassium in water, and add- 
ing thereto the oxide of silver. The ratio of the ingredients 
I am unable to state, as I have not hitherto directed my at- 
tention to this point, but have prepared the solution by trial 
until I obtained the desired result. 
By the process above described, we can at pleasure transfer 
