A DICTIONAEY 



OP 



AKTS, MANUFACTURES, AND MINES, 



Erratum and Omissions. 



Page 316 insert EXOGENOUS. A botanical term. See Brande's 'Dictionary of 



Science, Literature, and Art.' 

 325 for PORT read POST. 



534 insert GAIiVANISBI OP PLATES. The coating of iron plates with 

 zinc, &c. 



wjuuca , aiiu m aiiutner ne writes, * A decoction of Thlaspi (Shep- 

 herd's purse), fumes of phosphorus, and particularly of sulphur, as acting on silver in 

 the same way as iodine, and caloric, produce the same effect by oxidising the metal, for 

 from this cause proceeded in all these instances their extreme sensibility to light.' Niepce 

 died in July 1833. Daguerre proceeded -with his experiments for nearly six years, 

 before he succeeded in producing the desired results. The Daguerreotype process 

 depends on the production of a very delicate chemical compound of iodine and silver 

 on the surface of a carefully-prepared silver plate. The image is developed by 

 the action of mercurial vapour, and lastly rendered permanent, so far as the action 

 of light is concerned, by dissolving off the iodide of silver by hyposulphite of soda. 

 According to the first published description by Daguerre, the process is divided 

 into five operations. The first consists in polishing and cleaning the silver surface, 

 by friction, with cotton fleece imbued with olive-oil, upon the plate previously dusted 

 over with very finely-ground dry pumice-stone out of a muslin bag. The hand of the 

 operator should be moved round in circles of various dimensions. The plates should 

 be kid upon a sheet of paper solidly supported. The pumice must be ground to an 

 impalpable powder upon a porphyry slab with water, and then dried. The surface 

 is next to be rubbed with a dossil of cotton, slightly moistened with nitric acid, 

 diluted with sixteen parts of water, by applying the tuft to the mouth of the phial 

 of acid, and inverting it for a moment. Two or three such dossils should be used 

 in succession. The plate is lastly to be sprinkled with pumice-powder or Venetian 

 tripoli, and rubbed clean with cotton. 



The plate is then placed in a wire frame, with the silver surface uppermost, over a 

 spirit-lamp, meanwhile moving it so as to act equally on every part of the plate. In 

 about five minutes a whitish coating will indicate that this operation 'is completed. 

 The plate must now be laid upon a flat metal or marble slab to cool it quickly. The 

 white surface is to be brightened by rubbing it with cotton and pumice-powder. It 

 must be once more rubbed with the cotton imbued with acid, and afterwards dried by 



VOL. II. 



