METALLIC THREADS SOAP BUBBLE. 



purpose. The threads of the web of the spider were used, with 

 more or less success ; but the late Dr. "Wollaston invented a 

 beautiful expedient by which metallic threads of any degree of 

 fineness might be obtained. 



Let us suppose a piece of platinum wire, the one-hundredth 

 of an inch in diameter, a fineness easily obtainable by the process 

 of wire-drawing, to be extended along the axis of a cylindrical 

 mould, the one-fifth of an inch in diameter, the wire being thus 

 the twentieth part of the diameter of the mould. Let the mould 

 be then filled with silver in a state of fusion. When this is cold 

 we shall have a cylinder of silver, having in its axis a thread of 

 platinum the twentieth part of its diameter. 



This compound cylinder is then submitted to the common pro- 

 cess of wire-drawing, during which the platinum in its centre is 

 drawn with the silver, the proportion of their diameters being 

 still maintained. When the wire is drawn to the greatest degree 

 of fineness practicable, a piece of it is plunged in nitric acid, by 

 which the surrounding silver is dissolved, and the platinum wire 

 remains uncovered. 



By this process Dr. Wollaston obtained platinum wire so fine, 

 that thirty thousand pieces, placed side by side in, contact, would 

 not cover more than an inch. 



It would take one hundred and fifty pieces of this wire bound 

 together to form a thread as thick as a filament of raw silk. 



Although platinum is the heaviest of the known bodies, a mile 

 of this wire would not weigh more than a grain. 



Seven ounces of such wire would . extend from London to New. 

 York. 



15. Gold is subdivided into parts of inconceivable minuteness 

 by the gold beater. A pile of leaf gold, an inch high, would 

 contain 280000 leaves. The thickness of each leaf would there- 

 fore be the 280000th part of an inch. Yet such leaves, used for 

 gilding, not only produce a perfect coating of gold, but protect 

 the article they cover from the action of external agents that might 

 otherwise tarnish it. 



16. In the manufacture of gold embroidery, threads of silver 

 gilt are used. These threads- are produced by flattening very 

 finely drawn gilt wire. The gold which coats an inch of such a 

 thread weighs no more than the eight millionth part of an ounce. 

 Yet this inch may be divided into 100 parts, each of which will 

 be visible without a microscope. In this way the eight hundred 

 millionth part of an ounce of gold is rendered visible. But if 

 a microscope magnifying 500 times, be used, a portion of gold, 

 500 times less, that is the four hundred thousand millionth part 

 of an ounce will become visible ! 



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