Dr Turner's Chemical Examination of Wad. 21 T 



The iron eontainedin the Derbyshire Wad is wholly in the 

 state of peroxide. The grounds from which I infer the en- 

 tire absence of the protoxide it may not be superfluous to 

 state, as the method appears to me fully more delicate than 

 any in use. It is founded on a fact, which I have elsewhere 

 adverted to for another purpose,* that the formation of Prus- 

 sian blue from prussic acid by admixture with a salt of iron 

 and potash, does not occur when the iron is strictly in its 

 maximum of oxidation. A very minute quantity of the pro- 

 toxide, however, gives rise to the production of Prussian blue, 

 which is rendered obvious by dissolving the precipitated oxide 

 by a slight excess of sulphuric acid. — The Derbyshire Wad di- 

 gested in dilute sulphuric acid in a close vessel yielded a yel- 

 low-coloured solution, which, when mixed with prussic acid, 

 precipitated by pure potash, and acidulated with sulphuric 

 acid, did not give the least tint of blue. 



When this Wad is exposed to a white heat it loses 18.84< per 

 cent. ; namely, 10.29 of water, and 8.05 of oxygen. The re- 

 sidue was much contracted, of a black colour, and was power- 

 fully attracted on the approach of a magnet. It is hence 

 manifest that the oxygen was derived as well from the peroxide 

 of iron as from the manganese. A similar change ensues when 

 a mixture of pure peroxide of iron and oxide of manganese is 

 exposed to a red heat. 



According to the foregoing analysis, 100 parts of the Der- 

 byshire wad were resolved into 



Peroxide of iron, - - 52.34 



Deutoxide of manganese, - S8.59 



Water, - - 10.29 



Baryta, - - 5.40 



Insoluble earthy matter - 2.74 



99.86 

 The Wad from the Harz, of which Klaproth has given an 

 analysis in the 3d volume of his Contributions^ appears to have 

 been of the same nature as the preceding ; but it contained a 

 greater proportional quantity of manganese and baryta. 



Third species of Wad. 



* Edin. Med. and Surgical Journal, xxx. 344. 



