132 My. Wny on a Spathic Carbonate of Iron. 



There can be little doubt that the deposition of carbonate 

 of lime had occurred in the crystals simultaneously with that 

 of carbonate of iron, a circumstance of easy explanation from 

 the isomorphous relations of iron and lime in their carbonates. 



The simplest method of dissolving up the peroxide of iron 

 so as to obtain this pure carbonate of iron, appears to be to 

 digest the powdered mineral in strong hydrochloric acid till 

 all the black matter is removed, which occurs in a few minutes, 

 to wash and dry by a heat of 212°. 



The power which carbonate of iron in this state opposes to 

 the action of acids is well illustrated in another instance, in 

 which masses of the size of split peas were introduced into 

 commercial hydrochloric acid diluted with an equal bulk of 

 water, a state most favourable to the solution of a carbonate. 

 After digestion for a night, the acid remaining in excess, the 

 carbonate was found undissolved, the only effect being the 

 removal in solution of the hydrated peroxide and consequent 

 disintegration of the mineral. Some of the carbonate had 

 undoubtedly dissolved, but the greater part escaped. 



This separation of the constituents of the substance under 

 examination is a very distinct denial to the supposition that 

 they exist in a state of combination, and indicates at the same 

 time a very considerable resistance to external agencies. It 

 comes then to be an interesting mineralogical inquiry in what 

 way the peroxide of iron found its way into the mineral. In 

 the description of the " hydrous carbonate of iron," Dr. 

 Thomson states his belief that the peroxide had originally ex- 

 isted in the state of carbonate of the protoxide, but that by 

 exposure to the weather this had lost carbonic acid and be- 

 come peroxide. 



I might perhaps be allowed to go a step further, and sug- 

 gest the possibility that some of the lime which exists in the 

 mineral might, in solution in carbonic acid water, have pene- 

 trated it by infiltration, and that the excess of carbonic acid 

 would dissolve the carbonate of iron, and afterwards, upon 

 evaporation, leave it exposed as hydrated carbonate — a state 

 most favourable to atmospheric agency. 



The value of this mineral, however, in an oeconomical point 

 of view, constitutes unquestionably its chief interest, and on 

 this part of the subject it is to be regretted that only vague in- 

 formation can be afforded. 



The mineral came from Hull ; the only information that 

 accompanied it is, that "it forms a vein of from 4 to 10 fa- 

 thoms in thickness by upwards of 100 fathoms in width, within 

 about 15 miles of coal and railway." This of course would 

 afford an enormous supply. 



