CHAPTER VIII. 
ON THE CHEMISTRY OF GYPSUM, PLASTER OF PARIS, 
AND CEMENT PLASTER. 
BY E. H. S. BAILEY. 
Importance and Distribution of Gypsum. 
The commercial values of gypsum deposits have been recog- 
nized from very early ages, and in most of the civilized countries. 
It is interesting to go back to some of the oldest structures 
standing at the present time and note that, in some cases, plas- 
ter of Paris is the cementing material. On account of its fine- 
ness, porosity, whiteness, and the readiness with which it sets 
when mixed with water, it has been a favorite material for 
construction, especially in countries where there is a small rain- 
fall, and for interior decoration of portions of buildings not ex- 
posed to the weather. = 
Deposits of gypsum occur in many places in HKurope, espe- 
cially near Castalino, Italy, at Montmartre and Argentuil, near 
Paris, and at Derby, England. In the United States, gypsum 
is found in large quantities in Michigan, New York, lowa, Kan- 
sas, Virginia, Louisiana, Ohio, California, Colorado, Texas, and 
Arkansas, and is found in other states in smaller quantities. 
For many years the immense gypsum deposits of the Dominion 
of Canada, especially Nova Scotia, have furnished the eastern 
states with this material in the form of ‘‘ land plaster.’’ 
Formation of Gypsum Beds. 
What conditions have rendered possible the deposition of 
gypsum? Without giving details as to the geological occurrence 
of gypsum, there are several methods by which it is possible to 
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