Dr. Colquhoiin on the Argillaceous Ore of Iron. 231 



as universally as the clay, and in proportions which, in differ- 

 ent specimens, are susceptible of a similar variation. Its amount 

 is generally limited in its range from 0.5 to 1.5 per cent. In 

 one remarkable instance, to be afterwards more particularly 

 noticed, coal existed in the proportion of 3 per cent. ; but this 

 was a solitary exception to the general results, so far as my ex- 

 perience has gone. After the soluble portion of the ore has 

 been dissolved out by digestion in a dilute acid, the carbona- 

 ceous ingredient is found to remain behind, in a state of inter- 

 mixture with the earthy matter. This residue possesses more 

 or less of a black colour, according to the amount of carbona- 

 ceous matter that may be present. When calcined under free 

 exposure to the air, it changes its hue entirely, and, according 

 to the quantity of iron which it may have happened to contain, 

 it becomes sometimes pure white, sometimes yellowish white, 

 and sometimes reddish yellow. 



The state in which this carbonaceous or bituminous matter 

 exists in the ore seems indisputably to be, for the most part, 

 that of coal rather than pure charcoal. Indeed, from the com- 

 position of the minerals with which it generally occurs associat- 

 ed, it could hardly happen otherwise ; and the fact is put be- 

 yond doubt by the bituminous smoke and thick bituminous 

 liquor, which are found to pass off when many of the ores are 

 submitted to distillation. Some ores have even come under 

 our observation which threw up a sensible oily scum when im- 

 mersed in alcohol. 



The extraneous ingredients which may be next considered in 

 this mineralogical analysis of the ore are sulphur and phos- 

 phorus. Sulphur is frequently found in the state of iron py- 

 rites, which is disseminated sometimes in masses of various sizes, 

 and sometimes in veins through a stratum of iron ore. But as 

 it is an ingredient so prejudicial to the iron smelter as to war- 

 rant the rejection of any ore in which its presence is discovera- 

 ble by the naked eye, we shall limit our' examination of the 

 mineral to that range within which its employment by the iron 

 smelter is confined. And here its occurrence is by no means 

 uncommon. After analyzing eight different specimens, in order 

 to determine how far they might be affected by the presence 

 of sulphur, four proved to be completely free from it, and in 



