STATE GEOLOGIST. Bl 
oxide and water at red heat. Its solubility in water at the ordinary tem- 
perature is 0.14 parts, at 100° C. half of this amount. ‘Lime is dissolved 
more readily by a sugar solution, or glycerine, or an alcoholic iodine 
solution. 
Calcium oxide absorbs carbonic acid eagerly, especially at higher tem- 
peratures. On heating calcium oxide in a bulb to redness, removing the 
lamp and conducting carbon dioxide into the bulb in a strong current, it 
will be found that the lime becomes red hot in a few seconds, continuing 
to glow for fifteen minutes owing to the energetic absorption of the 
carbonic acid.* 
All these facts tend to show that lime is a very powerful base, combin- 
ing with acids with the greatest ease. Not only higher temperature, but 
also lower ones may bring about the union of silica and lime. When a 
mixture of quartz and lime hydrate is exposed to steam at a pressure 
of about 120 pounds to the square inch a reaction between them takes 
place; a hard, artificial sandstone is produced. This is the basis of the 
sand-lime brick industry. 
The varieties of rocks and minerals which are used as a source of 
carbonate of calcium will be discussed in the next chapter. Beside 
the carbonate, there are a few other lime compounds having a more or 
less important use in this same connection. 
Gypsum, composed of one molecule of calcium sulphate and two 
molecules of water, is a possible but not a probable source. Its value for 
other purposes is too great to make it applicable for cement-making ; be- 
sides, it would offer difficulties in manufacture which would be hard to 
overcome. The complete expulsion of the sulphuric acid would be a 
difficult task and the liability of retaining sulphur in some shape in the 
cement too great. Gypsum is used in the cement industry, but, not in 
direct connection with the cement burning itself. 
Though slag from blast furnaces is a source of calcium oxide, in a 
way, it is united with so much silica and alumina that it must be considered 
as furnishing silica rather than the base. 
In some processes of the chemical industries calcareous waste products 
may be used for the manufacture of cement. This applies especially to 
the manufacture of soda by the Solvay process, were calcitin chloride 
becomes available for cement making in large quantities. This material 
is chemically well suited for the purpose, since the chlorine is expelled with 
comparative ease. 
Dolomite.—The double carbonate of calcium and magnesium is known 
#s dolomite. Its percentage composition when pure is 54.35 per cent. cal- 
cium carbonate and 45.65 per cent. magnesium carbonate. 
Like limestone, it 1s subject to the same variations in composition 
and physical properties, as we have hard, compact dolomites as well as 
*Raoult, Compt rend. 92, pp. 189 and 1111. 
