L. TECHNOLOGY. 507 



and are made from the best portions of English ox-hides, 

 having 14 rows of stitching to bind the thicknesses together, 

 with a series of rivets running through between the rows. 

 3 A, March 17,128. 



ARTIFICIAL SHAGREEN. 



The substance known as shagreen, used in covering instru- 

 ment cases, telescopes, sword-hilts, etc., has generally been 

 supposed to be derived from the skins of sharks and rays. 

 We are now informed that an -imitation is made in Russia 

 which can scarcely be distinguished from the original, and 

 that this is prepared from the skins of horses or asses, soaked 

 in water and scraped, and, while the skin is still soft, small 

 seed, such as mustard or chenopodium, are imbedded in it, 

 and the surface afterward shaved down. By dyeing with 

 green, produced by the action of sal ammoniac or copper 

 filings, and drying, the imitation in question is satisfactorily 

 accomplished. 17 A. 



COPYING THE GRAIN" OF LEATHER. 



The Mechanics' Magazine informs us that by a recent pro- 

 cess a perfect electrotj^pe copy of the grain of leather can 

 now be produced, which may be used in imparting an exact 

 imitation of the grain of morocco, seal, or other skins upon 

 ordinary leather, so as to render them almost indistinguisha- 

 ble from the original. The deposit is attached to the man- 

 dril of an ordinary machine-roller, and, on passing the skin 

 through this, the finest variation of the grain or modification 

 of the surface, in imitation of the original, is produced. The 

 operator takes any skin that may be desired, and supplies 

 from it the means of preparing a fac simile of it. 3 A, May 

 12,324. 



DETERMINING TANNIN IN OAK BARK. 



A method lately introduced by Loewenthal for determin- 

 ing the amount of tannin in oak bark is based upon the fact 

 that tannin, in the presence of indigo, is decomposed by per- 

 manganate of potash in such a manner that, with the final dis- 

 appearance of the blue color, the last trace of the tannin is 

 also decomposed. For this inquiry the following liquids are 

 needed : first, a solution of indigo carmine ; second, a solution 



