Mr. Way on a Spathic Carbonate of Iron. 131 



though in much smaller quantity; and the analyses by Ear- 

 thier of nineteen varieties of iron ore from the coal beds of 

 France exhibit the uniform presence of the oxide of this metal 

 in a proportion varying from 0*5 to 4 per cent. 



The absence of manganese is perhaps, however, less inter- 

 esting in a scientific than in an oeconomical point of view, and 

 can easily be conceived in a crystallized mineral, which ap- 

 pears to have undergone so little alteration. 



Its freedom from silica (with the exception of a mere trace 

 not mentioned in the analyses, and existing as grains of quartz 

 and not in combination), from alumina, magnesia and phos- 

 phoric acid, are also matters more affecting the value of this 

 ore as a source of iron than its interest as a subject of scien- 

 tific inquiry. 



The action of acids upon the mineral is peculiar, and throws 

 some light on its constitution and the probable circumstances 

 of its formation. When treated in the state of fine powder 

 with diluted hydrochloric acid it is gradually dissolved with 

 effervescence, but the action is by no means rapid ; if heat be 

 applied considerably more effect is produced, but not such as 

 we are accustomed to witness in the solution of carbonates. 



If the acid be poured off after a short digestion with heat 

 upon the powdered mineral, the residue undissolved is in the 

 state of a white crystalline powder, which dissolves very slowly 

 even in concentrated, and scarcely at all in dilute mineral or 

 in vegetable acids. 



Upon examination, this crystalline carbonate was seen under 

 the microscope to consist of well-defined perfectly transparent 

 crystals, having the rhomboidal form of calc spar. Notwith- 

 standing the prolonged action of acids to which the mineral 

 had been subjected, the crystals were found to retain a con- 

 siderable quantity of lime. It was thought advisable there- 

 fore to subject the substance to analysis. The result was : — 



Protoxide of iron 56* 14 



Carbonic acid ; . 39'03 



Lime S'O* 



100-21 

 Its composition is therefore 



Carbonate of protoxide of iron . 91*24 



Carbonate of lime 8-97 



100-21 



It will be seen that the carbonate of lime is here in larger 

 proportion than in the original mineral, which should be the 

 case if the digestion in acids removes only or principally the 

 peroxide of iron. 



K2 



