Art. XXIX.—On the alkalinity of Carbonate of Lime.
[Read before the Wellington Philosophical Society, July 17, 1869.]
Carbonate of Lime is described, in chemical works, as neutral to test paper, but this scarcely agreeing with the results of observations I have had to make upon this point, in the course of other investigations, I beg to give these results, which are as follows:—
1st. Carbonate of lime, prepared by igniting pure oxalate of lime in a close crucible, at a dull-red heat, gives an intense alkaline reaction with reddened litmus paper, after moistening with distilled water, or after reignition with pure carbonate of ammonia.
2nd. Carbonate of lime prepared directly from chloride of calcium and bi-carbonate of soda, by admixture of their aqueous solutions, and washing the ensuing precipitate till all the soda was removed, gave the same reaction with test paper.
3rd. Limestone, shells (calcareous), calc-spar crystals, and arragonite, are all strongly alkaline to test paper (at least, the samples I have tried were), the powder of any of these substances, washed with distilled water for many days, does not seem to lose any of this alkalinity.
Lastly (and I think, conclusively), precipitated carbonate of lime, prepared by either of the above processes, when agitated with weak hydrochloric acid, in successive quantities, until gradually reduced to a minute proportion of its original bulk, still manifests this reaction to an eminent degree; indeed, the solution could not be rendered permanently acid till the whole of the carbonate was dissolved.
It seems impossible, under these circumstances, to attribute this reaction to the accidental presence of free magnesia or lime, sub-carbonate of lime, or alkaline carbonates, in the precipitate; this reaction may therefore, I think, fairly be attributed to the carbonate of lime.