Chemical Observations upon Spathic Iron. 323 



that all kinds of ores are mixed in roasting, and that the 

 proportion of magnesia in the mass is not always so great 

 as that found by M. Drappier; and that, lastly, it is some- 

 times necessary to add mild ore to it. 



Without doubt, after a long-continued exposure, an ore 

 of easy fusibility might be always obtained ; but as this te- 

 dious method is attended with very great inconvenience, se- 

 veral processes are in use to shorten the time : the most 

 practicable is to mix some mild ore with the ore of large 

 lamina newly dug; in this case the proportion. of the mag- 

 nesia is endeavoured to be diminished. 



Some ores, as well as that of Eisen- Arts, contain quartz, 

 calcareous carbonate, and argil, the most advantageous mix- 

 ture to promote the fusion of the magnesia ; but it is neces- 

 sary to get rid of the greater part of this earth by exposing 

 to the air the most refractory species of spathic ore. 



In some iron-works, also, they mix with the spathic iron 

 carbonate of lime and ochrey ores, which, as is well known, 

 usually contain argil and sand : flux for the magnesia is thus 

 composed. 



It is not improbable that the oxide of manganese facili- 

 tates fusion a little; at least, by repeating the experiments 

 of Bergman upon the vitrification of magnesia, I think I 

 have observed that this metallic oxide produces a very great 

 fluidity in glass. 



To conclude; it is necessary to remark, that all the man- 

 ganese contained in these ores does not vitrify when it is in 

 great proportion, a part of it being reduced with the iron, 

 . and united to the melted metal*. All the trials I made 

 with the specimen of Allevard yielded me buttons of white 

 metal, which contained manganese in great abundance. That 

 of Vaunaveys, and a melting of Vierzon, only afforded some 

 slight traces of manganese in the same circumstances. 



The method I employed consisted in dissolving the metal 

 in aqua regia : I afterwards precipitated with ammonia, and 

 heated the precipitate to redness, in a silver crucible, with 



♦ At least in the docimastic experiments. 



y 2 caustic 



