•1« 



■;2?:rs'?''s 



Old ores more 

 fusible than 

 SL«vr, 



Magnesia 

 most iiiiurious 

 to rich ores. 



Ko external 

 marks of its 

 jprcience. 



Application of 

 heal alone the 

 best test. 



Marks of a re- 

 fractory ore. 



Marks of a fu- 

 sible ore. 



Indication of 

 manganese. 



Loss in roast- 

 ing. 



Quantities of 



ON SPARRY inON ORES. 



contained nothing but sulphate of magnesia, and a little 

 sulphate of lime; which suits could have been produced 

 only by the action of the sulphuric acid, arising from the 

 pyrites, on the earthy substances contained in the ore. 



Mr. Descotils quotes letters of several well informed per- 

 sons, and worthy of credit, v/ho, in agreeing on the point 

 that sparry iron ores recently extracted and roasted are more 

 difficult of fasion, and less productive, than those that have 

 remained three or four years in the open air, give ftiil more 

 force to his theory. 



Though it is certain, that the presence of magnesia in 

 iron ores diminishes their fusibility more or less, the author 

 of the memoir observes however, that, if it be accompanied 

 with a sufficient quantity of lime, silex, and alumine, or of 

 oxide of manganese, it is not so injurious, because it be- 

 comes fusible by combining with these substances. 



Conceiving the advantage iron masters would find in hav- 

 iiig an easy method of knowing by simple inspection a free 

 from a refractory ore, Mr. Descotils has examined, whether 

 among the external characteristics of these substances there 

 might not be some, by which these properties could be dis- 

 tinguished : but the strictest scrutiny in this respect waS 

 without success. He has been obliged therefore, to have 

 recourse to chemical means, and what he found most to the 

 purpose was fusing the ore without the addition of any flwj^* 



If a^te^ this operation the matter present itself in a grayish, 

 earth}^ friable mass, interspersed with small globules of cast 

 iron, it is a proof, that the ore is niagne&ian, and consequently 

 more or less refractory. 



But on the contrary, if a well fused button be obtained, 

 with brown and not very abundant scoriai, the ore is fusible, 

 and contains but little magnesia. 



When the scoriae are green, they indicate the presence of 

 oxide of manganese, part of which is reduced, and mixes 

 with the cast iron, by a high and long continued heat. 



The least altered kinds of sparry ores, that Mr. Descotils 

 assayed, lost in roaating from 31 to 37 per cent. The altered 

 or free ores lost at most but 14 per cent, and this loss was- 

 merely water. 



The quantities of magnesia and manganese vary greatly j 

 , sometimes 



