It is ordinarily prepared by the fermentation of sugar or starch, brought about by the addition of putrefying cheese, calcium carbonate being added to neutralize the acids formed in the process.
When cryolite is used for the preparation of alum, it is mixed with calcium carbonate and heated.
When the proportion of calcium carbonate in the blue mud is considerable there results a calcareous ooze, which when found on the continental slope and in enclosed seas is largely composed of remains of deep-sea corals and bottom-living foraminif era, pelagic organisms including pteropods being less frequently represented.
However, until more is known of the exact chemical composition of naturalas contrasted with agriculturalsoils, and until more is known of the physiological effects of lime, it is impossible to decide the vexed question of the relation of limeloving and lime-shunning plants to the presence or absence of calcium carbonate in the soil.
On entering the first purifier, which contains calcium thiocarbonate and other combinations of calcium and sulphur in small quantity, the sulphuretted hydrogen and disulphide vapour have practically no action upon the material, but the carbon dioxide immediately attacks the calcium thiocarbonate, forming calcium carbonate with the production of carbon disulphide vapour, which is carried over with the gas into the second box.
There are, therefore, a number of agencies, all of which operate in shoal waters on the lee side of islands, or in shallow lagoons in such regions as the Bahamas, and the result of all these is to throw down calcium carbonate from solution in sea-water as minute needle-shaped crystals or little balls of aragonite.
The material which chemists call calcium carbonate is met with in a comparatively pure state in chalk.
Primarily but a slight deposit is formed (none until the concentration arrives at specific gravity 1.0509), this deposit consisting for the most part of calcium carbonate and ferric oxide.
It is, however, a curious question how, considering the increase of carbonic acid by the decomposition of organic bodies and possible submarine exhalations of volcanic origin, the water has not in some places become saturated and a precipitate of amorphous calcium carbonate formed in the deepest water.
The proportion of calcium carbonate varies greatly according to the amount of foraminifera and other calcareous organisms which it contains.