Chemical Science. 407 



jury to the painting, lias been devised by Signer StefFano 

 Barezzi, of Milan. Tiie picture is covered with a prepared 

 canvass to which it adheres, and is thus detached from the 

 wall. The canvass is afterwards applied to another wall, to 

 which the painting again attaches itself without the least trait 

 being destroyed. The practicability of this method has been 

 successfully proved, and the inventor is now employed in trans- 

 ferring a large fresco from the church Delia Pace, at Rome. 

 Great expectations are entertained that he will be able thus to 

 rescue from destruction the celebrated Cena of Leonardo da 

 Vinci. — Magazine of Fine Arts, 474.* 



11. Green Paint. — Gas tar, mixed with- yellow ochre, makes 

 an excellent green paint, very useful for preserving coarse wood 

 work or other articles. 



II. Chemical Science. 



§ Chemistry. 



1. Curious effect of Sea Water upon Cast Iron. — In a recent 

 visit to Plymouth, Mr. Hatchett obtained from Mr. Whidbey, a 

 portion of a cast-iron gun, which had long been immersed in 

 sea water : it was incrusted to the depth of an inch with a 

 substance having all the exterior characters of impure plum- 

 bago ; easily sectile, greasy to the touch, and leaving a black 

 streak upon paper. This substance, digested in water, afforded 

 a small quantity of muriate of iron, but was not otherwise 

 affected. Digested in muriatic acid, a considerable portion 

 was dissolved without any eflTervescence ; and the solution had 

 the properties of pure muriate of iron, with a trace of manga- 

 nese. The insoluble portion, when collected upon a filter, 

 washed, and dried, was a shining black powder, very soft and 

 unctuous to the touch, and apparently pure plumbago. At 

 Dr. Wollaston's suggestion, I examined it for manganese : I 

 deflagrated a portion of it with chlorate of potassa, dissolved 

 the residue in muriatic acid, and threw down oxide of iron by 

 pure ammonia; the neutral solution was filtered, and evapo- 

 rated to dryness ; the dry salt was entirely dissipated by heat, 

 and gave no trace of manganese. The relative proportions of 

 the component parts of this substance were, 



Oxide of iron - - 81 

 Plumbago - - - 16 



97 

 Anchors, and other articles of wrought iron, wlien similarly 

 exposed are only su|)erfi('ially oxidized, and exhibit no other 

 peculiar appearance. There can, therefore, be little doubt that 



* Is not till- " Last Siipixr" of L. d.i \ inci already lU'stroycd ? Ed. 



