3-20 Chemical Observations ?ipon Spathic trom 



refractory, is extremely fusible, and we may obtain iron 

 from it by the Catalan method with much success. 



It is evident that in these treatments even the metals are 

 oxidated, and the sulphuretted iror, which generally accom- 

 panies this spathic iron, is converted imo sulphate, particu- 

 larly when roasting is made use of* : this sulphate seems t<a 

 be taken away by the rains, or by the water which has been 

 passed through the heaps of the mineral ; but this separa- 

 tion does not explain the augmtnation of fusibility; it 

 seems, on the contrary, that this qua'i'y ought to be dimi- 

 nished, because the sulphur is necessarily left in less propor- 

 tion in the mineral ; and we know that this principle renders 

 the iron more fusible. In order to ascertain the true cause 

 of this, let us first inquire into the cause of the refractory 

 property of certain spathic ores. 



It is well ascertained that the ores of great laminae, to 

 which in Dauphine the name of ma'dlat is given, are every 

 where regarded as the most difficult to melt. This ore, as 

 has been said above, is precisely that in which magnesia 

 abounds; and we know that this earth vitrifies with diffi- 

 culty. Bergman, in his dissertation upon this substance, 

 expressly says, that it does not enter into fusion, except with 

 silex, argil, and lime, or with fluor spar f ; and iM. Lampa- 

 dius has made some experiments of the same kind, from 

 which he concludes that magnesia diminishes the fusibility 

 of mixtures into which it is introduced, if it does not destroy 

 it completely. 



* I shall say a few words on the subject of roasting. — We know that the 

 ore of spathic iron is found in ridges mixed with quartz, calcareous spar, and 

 sometimes argil, as at Eisen-Arts, according lo M. Rambourg, and a quantity 

 of ferruginous pyrites more or less considerable. The ores of Old Dauphiny 

 and Mor.t Elanc are particularly in these circumstances. The roasting sepa-< 

 rates a portion of sulphur; it drives ofT the carbonic acid, which would make 

 the beans' swell up and augment the weight of the ore, and consequently the 

 expense of carriage to the furnace; it lastly destroys the cohesion, and gives 

 the workmen a great facility in separating the quartz and other foreign sub- 

 »tances : but one would think that, the pyrites being then confounded with 

 spathic ore by their colour, the workmen could not separate them, and that 

 in lime they would effloresce. 



•f Darcet melted a stone (Briar.^on chalk) which contained a great propor- 

 tion of ibis, bv mixing it with gypsum. 



In 



