On Bleaching, 55 



of the nltro-mnrlatic acid, it will no longer be doubted that 

 it is chiefly owing to the fulphurated phol'phorized platina. 



In fiipport ot my conjeSure, I fliall fav a few words rc- 

 fpecting the fulphurcts of which I havefpoken. 



The lulphiirel of mercury, or cinnabar, contains the metal 

 in its natural ftate, and not, as is commonly faid, in that of 

 oxide; for, notwithltanding the difpofition of mercury to 

 unite with oxygen, concentrated nitric acid does not attack 

 cinnabar. 



Copper takes up 28 parts in 100 of fulphur, and never lefs: 

 it can, however, dilTolve fulphuret of copper in various pro- 

 portions, as may be feen in my cflays on black copper. If 

 copper containing fulphuret be expofed to nitrous acid of 12 

 or 15 degrees '■'', the copper will be dilTolved ; and fulphuret, 

 which will feparate itfelf under the form of a blackifti blue 

 powder, cannot be oxidated but in a very ftrong heat. 



r applied feveral times an acid of 35 degrees f to Ameri- 

 can filver ore containing fulphurets of copper, lead, iron, 

 antimony, zinc, mangancfe, &c., and found that, if thefe 

 mixtures were not heated, the greater part of the metals were 

 attacked by the acid, the whole, or at leaft the greater part, 

 of the filver in the (tate of fulphuret excepted; from which 

 we may conclude that this fulphuret is one of thofe which 

 refift the a&ion of the nitric acid much more than the metal 

 itfelf. It is very probable that this is the cafe with many 

 others, which I do not at prefent recolleft. 



[To be continued.] 



IX. On Bleaching. Bj' a Corrc/pondent, 

 To the Editor of the Philo/ophical Magazine. 



SIB, 



HE importance of the new mode of bleaching to the 

 principal manufietures of this country renders it worthy the 

 noft minute and accurate attention. Before your publication of 

 O'Reilly's EfTay, no complete treatife on the modern fyllem 

 had appeared. That of Berthollet, the difcoverer, thongh in 

 many particulars very defeftive, was undoubtedly the belt 

 adapted to inltnict the practical manufadlurer, who cannot be 

 fuppofed intimate with the minutiae of the laboratory. The in- 



"■ If thcfc are degrees of Haumc's areometer, as may be prcfumcd, tluy 

 indicate a fpcciiic fr.vit/ of from ioii9 to j'ii4. 

 f Sptcifi; giavity oJ i'3i4. 



D 4 definite 



