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-cai'bonate 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 hydro- 

 chloric 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. 



Art. XXX. — On the absorptive properties of Silica ; and its direct hydration 

 by contact with water. By W. Skey, Analyst to the Geological Survey 

 of New Zealand. 



[Bead before the Wellington Philosophical Society, July 17, 1869.] 



In No. 157 of the "London Chemical News," I communicated the fact that 

 silica is hydrated and dissolved by aqueous solution of ammonia. Evidence 

 in favour of this being given in a recent number of the same Journal, together 

 with particulars as to the amount of this solubility, I thought it desirable to 

 ascertain whether ammonia is absolutely necessary to ensure this, the first of 

 these reactions, the hydration of the silica, it occurred to me that water might 

 effect it of itself; — the action of ammonia, in this instance, being confined 

 to bringing the silica, thus hydrated, into solution. 



The following experiments tend to show this assumption to be correct. 



Rock-crystal, finely pulverized in an agate mortar, then agitated with 

 water, did not completely subside, even after the lapse of some days ; the water 

 remained turbid like clay-water, and like it, is soon clarified by the addition of 

 an acid or a neutral salt. 



The effects of such additions would, I conceive, rather retard the precipi- 

 tation of the silica, by increasing the gravity of the fluid, were it not that 

 combination between the silica and the water had commenced — were it not 

 also for an affinity of this substance for water under these conditions, — feeble, 

 no doubt, as to intensity, but insatiable as to quantity. 



There appears to be one weak point in the evidence here tendered, namely, 

 that agate (the substance of the mortar used), is not pure silica ; still, it is so 

 nearly pure, that upon the whole it is, I think, quite safe to leave this matter 

 out of further consideration. 



In reference to other absorptive properties of silica, I find that massive 

 quartz, rock-crystal, and silica, prepared for estimation in the usual way, take 

 sesqui -oxide of iron from solution of its acetate, but not from the chloride. 



