516 



ON SPARRY IRON ORES. 



whi h he are 

 deprived ot it. 



Their moc^e 

 of operdticn. 



Hassenfrata; 

 started some 

 objections, but 

 appears to have 

 Ifiven them up. 



The author 

 has repealed 

 his experi- 

 ments, and 

 made fresh. 



Experiment 

 with ore of 

 Elba. 



Effect not ow- 

 ing to its being 

 powdered. 



R«riaotoflness 



of the principle of their infusibility, which consist chiefly in 

 exposure to the air and raiu, eitlier before or alter roasting, 

 Mr. Descotils conjectured, that these piocestes had no other 

 effect than that of separating- the magnesia. 



In the lirst case, that is to say, when these ores were ex-* 

 posed to the air before roasting, he supposed, that this earth 

 was dissolved in the slate of carbonate by the rain, in the 

 second, on the contrary, he ascribed this ettt-ct to the sulphu- 

 ric acid developed by the eiflorescence of the pyrites, with 

 which the iron spar is aunost always accompatiied. 



Since that period Mr, Descotils ht s ccumiumicatedtothis 

 assenably a second memoir, in which he fu.nishes substan- 

 tial proofs of the explanations he had oiie^ed in the lor- 

 mer paper as merely conjectural ; at the same time avails 

 himself of them to answer some objections, that had been 

 advanced by Mr. Has?enfratz. The latter gevjtleman how- 

 ^ver,^ after having made some fresh experiments and obser- 

 vations, has withdrawn his memoir, w-hich the class had re-» 

 fer red to the same committee: we shall not therefore enter 

 into any discussion of the points, on which these two learned 

 chemists differed, but shall consider the facts related by Mr, 

 Descotils, and the conclusion he has deduced from them, as 

 jf they had never been disputed. * 



On this second occtislon Mr. Descotils has repeated his 

 former experiments, which gave him the same results. He 

 has likewise made new ones; and all, mutually supporting 

 each other, have only confirmed him in his opinion. But 

 let us relate some of these experiments.. 



He exposed to the fire a mixture of fifteen parts of mag-» 

 nesia, and a hundred parts of iron ore from the isle of Elba, 

 finely powdered ; and the result he obtained was perfectly 

 similar to what every magnesian iron spar has furnished him. 



To ascertain whether the division of the particles of the 

 substance had any influence on its fusibility, lie made atrial 

 with part of the same specimen of iron ore of Elba, without 

 wasting or powdering it, and he obtained a perfectly compact 

 button, at a degree of heat similar to what would have been 

 requisite for an assay of earthy iron ore with the addition of 

 borax. 



This fact shews, snys the author, that cohesion does not 



diminish 



