of the Argillaceous Iron-^Ore. 255 



the action 6F the assay furnace, and shall conclude this part 

 of the memoir by an examination of the metallic button and 

 scoria, with a view not merely to determine the actual results 

 of any assay which has been made, but also to discover how 

 far it has been successfully conducted, or in what respects it 

 may on a subsequent trial be amended^ 



In following out the method which has now been laid down, 

 the first point is to state those principles which have been 

 fixed by experience, regarding the fusible or fusifying nature 

 of the ingredients which are usually found associated in the 

 smelting furnace. Upon this subject the three following ge- 

 neral rules will be found of universal application. 



1. The earths which usually occur in the ores of iron are 

 silica, alumina, lime, and magnesia. Each of these is infusible 

 when exposed j5^r se to the most elevated temperature of a 

 furnace. The oxides of iron are fusible under the same cir- 

 cumstances. 



2. Very few binary mixtures of these bodies afford com- 

 pounds fusible at the temperature of the blast-furnace. The 

 cases in which such compounds are produced are the follow- 

 ing. Silica mixed with its own weight of lime melts under a 

 strong heat, into a sort of enamel : it is fusible also with ra- 

 ther more than its own weight of oxide of iron or of oxide of 

 manganese. Compounds possessed of considerable fusibility 

 in very high temperatures are likewise afforded by oxide of 

 iron, when mixed with less than its own weight of lime or of 

 alumina ; or with a quarter of its weight of magnesia. 



3. A large proportion of the ternary mixtures of the earths 

 and the oxides, and a still larger number of their quaternary 

 mixtures, are fusible in the furnace. In these mixtures, if any 

 one of the ingredients, excepting magnesia, predominates con- 

 siderably over the others, the fusibility of the compound may 

 be considered as almost certain. But magnesia, whenever its 

 quantity exceeds that of the other ingi-edients of the mixture, 

 has a remarkable effect in rendering it refractory. 



It will be observed that in each of these complex mixtures, 

 there is no single ingredient more conducive to fusibility than 

 the oxide of iron or of manganese, and none more adverse to 

 it than magnesia. ^ 



