of the Argillaceous Iron-Ore. 257 



celain, or an infusible mass^ according to the proportions of 

 the mixture. ^ ys^ 



If the alumina predominate, many mixtures will yield a 

 porcelain, but none will afford a glass. 



If silica exceed, a porcelain or an enamel is frequently pro- 

 cured, and it is probable that even a glass may be attaiBt, 

 able.* 



From a due consideration of these experiments of Mr Kir- 

 wan, and of the preceding general rules, it will not be diffi- 

 cult for the assayist, with a little perseverance, to succeed in 

 adapting an appropriate flux to his ore. 



In doing this, he will find that the earthy ingredients which 

 are most frequently present to excess in the common argilla- 

 ceous ironstone, are clay and silica. Both of these substances 

 will easily vitrify in the furnace with the addition of lime. 

 Lime is therefore the principal flux which is employed for 



• Elements of Mineralogy, vol. i. p. 72* The fusibility of mixtures 

 of the earths and metallic oxides has been made the subject of an elabo- 

 rate course of investigation, by several other eminent chemists besides Mr 

 Kirwan. Among these may be mentioned Achard, (Memoirs of the 

 Academy of Berlin, 1779, 1780. Journal de Physique, xxii. 179, 300. 

 xxiv. 280, xxv. 137. J, Gerhard, (Versuche epier Geschichte der Mineral- 

 reich, vol. ii. Journal de Physique, xxviii. 34. J, Klaproth, (Beitrage %ur 

 chem. Kennt, der Miner alkorper, i. l.J, and Lampadius, ( Handhuch der 

 Allgemeine Hilttenkunde, i. 127. Journal des Mines, xviii. 171. J It 

 would be a highly interesting inquiry to examine in elevated temperatures 

 the habitudes of similar mixtures of earths and metallic oxides, made in 

 conformity with the prime equivalent proportions of these substances. 

 Hitherto the only system of investigation pursued on this subject has been 

 by subjecting to the action of heat an endless variety of binary, ternary, 

 and quaternary mixtures. But when we consider the number of distinct 

 substances and the infinity of their possible combinations whose reciprocal 

 action in high temperatures it is of importance to know, it is almost a 

 hopeless task to endeavour to subject each of these successively to the test 

 of experiment. Now, however, that the combining proportions of bodies 

 have been ascertained, the metallurgist is in possession of an infallible rule 

 for his guidance in compounding earthy mixtures ; and in every future 

 prosecution of such an inquiry, he would, of course, systematically mix 

 the substances to be experimented upon, in conformity with their prime 

 equivalent weights. The number of the experiments which he would find 

 it necessary to make, would be thus most materially abridged, while, at 

 the same time, the attainment of important and decisive results would be 

 rendered far more certain. 



