PROCEEDINGS OF GEOLOGICAL SOCIETIES. 
181 
It is with lime especially, and its eomponnds, that we hare to do. Lime 
is composed of one equivalent of calcium and one of oxysren. You are all 
familiar with the properties of lime — an amorphous body, white, or more 
or less coloured with impurity, and which, on the application of water, 
slacks ; that is, it absorbs water, the water enters into combination with 
it, and becomes solid, and on its passinoj from the liquid to the solid state, 
a large amount of heat is evolved. The lime falls to pieces, having become 
hydrated, or, in common language, slacked. It is slightly soluble in water, 
as every one knows, producing the well-known liquid called lime-water. 
When combined with water — for it must be hydrated — it unites readily 
with carbonic acid, forming carbonate of lime. 
Carbonate of lime is a mineral which occurs very extensively in nature, 
forming beds of chalk, limestone, and two very important minerals, namely, 
calcite and arragonite. Carbonate of lime is a compound of one equivalent 
of carbonic acid and one of lime. It is known in three distinct states. 
There is, first, the amorphous or chalk-like state : we will call it chalk. It 
is perfectly non-crystalline or amorphous. There is, then, the form of 
arragonite which occurs in prismatic crystals, and belongs to the prismatic 
eystera. The third form of carbonate of lime is that of calcite or calcspar, 
w hich is rhombohedral, crystallizing in the beautiful rhombohcdral crystals 
with which every mineralogist is familiar. Arragonite varies in specific 
gravity from 2-93 to 3 01. This is a point to note. The calcite has alower 
specific gravity, ranging from 2T)9 to 2-75, so that not only in their crys- 
talline system, but also in specific gravity, are these two minerals distin- 
guished clearly from each other. 
The next point is the solubility of carbonate of lime. In treating this 
subject of chemical geology, the lecturer was selecting all those points 
which he conceived had a direct geological bearing; and it is requisite to 
pay rather close attention, which, perhaps, may be considered tedious, to 
this part of our subject. One part of carbonate of lime dissolves in 110,000 
parts of pure water, in round numbers : it is 110,132 parts really. This car- 
bonate of lime dissolves to a much greater extent when carbonic acid is 
passed through the water, and it then forms what is termed bicarbonate of 
lime. One part of carbonate of lime dissolves in 998 parts of water con- 
taining carbonic acid, according to Bischoff, the carbonic acid being passed 
through the water for an hour. He has made several experiments upon 
this subject, which are remarkable. He finds that the solubility varies to 
a great extent with tlie nature of the carbonate of lime operated upon. 
Tiius, 11-15 parts of chalk were dissolved in 10,000 parts of water by pass- 
ing carbonic acid through for an hour. He performed this experiment 
three times, and each time he obtnined pretty nearly the same result ; 
but, when he tried the experiment with carbonate of lime precipitated from 
a salt of lime, passing the carbonic acid through for about the same tune as 
he did in the experiments with the chalk, he found that 28 parts dissolved 
in 10,000 parts of water. There is another very striking statement, but 
which will require further corroboration. It is, that burnt muschelkalk 
dissolved to the extent of 135-3 parts in 10,000 parts of water, by passing 
carbonic acid through the water for an hour and a half. 
In passing, he would mention the fact, that when arragonite is exposed 
to a red-heat, it falls to powder ; and it was supposed for a long time that 
this powder consisted of minute rhombs of calcite. This, however, is 
denied by Gustave Kose, who contends that the powder is strictly amor- 
phous. ,1 J- 
Let us now consider the mode of formation of arragonite, or the condi- 
