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l’ROOFS OF THE PROPERTIES OF LIME.

Rationale. ..Tht carbonic acid unites with the dissolved lime,and forms carbonate of lime, which on account of its insolubi-lity is precipitated.

Remark. ..Though lime saturated with carbonic acid formsan insoluble compound, yet when super-saturaied with it, theproduct is re-dissolved, as will be evident from the following

Experiment III.

Lime sur-saluraled with carbonic acid is soluble in water.

Add to a jar about one-fourth filled with lime-water, gradually,"a very small quantity of water impregnated with carbonic acid,a milkiness will ensue, because the carbonic acid forms withthe lime an insoluble compound. On adding more of the water,and shaking the jar as these additions are made, the milkinessat last disappears, and the whole precipitate becomes re-dissolv-ed. Hence it is evident that lime, with a small quantity of car-bonic acid, is insoluble; and, with a larger quantity, becomesagain dissolved in water.

The carbonate of lime dissolved by an excess of acid is againseparated, when this excess is driven oft'. Thus boiling, whichexpels the superabundant acid, again precipitates the carbonate.

Remark. ..It is thus that nature dissolves calcareous masses,which have been collected and deposited by the waters. Whenthe waters by their exposure to the air, lose that quantity of car-bonic acid which favoured the solution of the lime, deposits areformed, and hence the stalactites and incrustations found in ca-verns, springs, &c. and even the foliaceous calcareous strata ofrocks, which without doubt have been held in solution.

When these waters suddenly lose the acid which was essential tothe solution, there is an irregular precipitation; hence those tendercalcareous cellular stones, and perhaps also the spongy tuffs-,but if the evaporation of the carbonic acid takes place slowly, itproduces crystallizations, such as stalactites, Ac. All this there-