PLYMOUTH INSTITUTION. 233 



repeated, sometimes more than once, by a succession of lighter ham- 

 mers, so that 376 grains of gold are thus finally extended into 2,000 

 leaves of three inches and three tenths square, making in all 80 

 books, each containing 25 leaves. The metal is consequently re- 

 duced to the thinness of the 282,000th part of an inch, and every 

 leaf w^eighs rather less than one fifth of a grain. A single leaf of 

 this may be divided into 2,000,000 parts, each of v^rhich will be dis- 

 tinctly visible. 



A pound of so gross a substance as cotton may be spun into a 

 thread exceeding 100 miles in length; and the celebrated Boyle 

 speaks of a thread of silk 300 yards in length, which weighed no 

 more than 3^ grains. 



In the manufacture of embroidery it is necessary to obtain gilt- 

 silver threads of an extreme fineness : in order to effect this a cylin- 

 drical bar of silver, weighing 360 ounces, is coated. with about two 

 ounces of gold ; this bar is then wire-drawn by passing it through 

 a steel plate, (a diagram of which was shown,) until it is reduced 

 to a thread so fine that 3,400 feet of it will weigh less than an 

 ounce ; the wire is then flattened by passing it between polished steel 

 rollers, under a severe pressure, by which its length is so much in- 

 creased that 4,000 feet weigh only one ounce, the thickness of the 

 gold being the 4 or 5,000,000th part of an inch. One foot of this 

 gilt wire will weigh the 4,000th part of an ounce. The proportion 

 of the gold to the silver was originally that of 2 to 360, or 1 to 180. 

 Since the same proportion is observed after the bar has been wire- 

 drawn, it follows that the quantity of gold which covers one foot of 

 the fine wire is about the 180th part of the 4,000th of an ounce, that 

 is the 720,000th of an ounce. The quantity of gold which covers 

 an inch of this wire will be one twelfth of that which covers a foot, 

 hence this quantity will be the 8,640,000th part of an ounce. If 

 this be again divided into lOO equal pai'ts, every part will be dis- 

 tinctly visible without the aid of a magnifying power. The gold 

 which covers this small but visible portion is, the 864,000,000th 

 part of an ounce. But we may carry this even farther : — this por- 

 tion of the wire may be viewed witli a microscope which magnifies 

 500 times, so that the 500th part of it will become visible. In this 

 manner an ounce of gold may be divided into 432 billion parts; 

 each part will possess all the characters and qualities which are 

 found in the largest masses of the metal ; it retains its solidity, tex- 

 ture and colour ; it resists the same agents, and enters into combi- 

 nation with the same substances. If the gilt wire be dipped in 

 nitric acid, the silver within the coating will be dissolved, but the 



VOL. II.— 1833. f2 



