122 NEW YORK STATE MUSEUM 



As an adulteramt it is sometimes known as " terra alba " and 

 is used in food and medical preparations. 



In the calcined state, as plaster of paris, the uses of gypsum 

 are too numerous to catalogue, but the greater part of the 

 product is used in wall plaster and in wall washes. Dentists 

 use large quantities in making plates, surgeons use it to hold 

 broken limbs in place, and sculptors find it an invaluable 

 material for making masks and casts. To the antiquary it is 

 invaluable in taking impressions of inscriptions, statuary etc. 

 It is used to some extent in the manufacture of wine to retard 

 fermentation (the plastering of the wine) and absorb water. It 

 has been discovered that blocks of plaster of paris are a good 

 fireproofing material, because of the fact that it is a bad con- 

 ductor of heat, being said to be superior to hollow brick. 



It has ordinarily been supposed that the manufacture of slow 

 setting, or cement, plaster is a new feature of the gypsum indus- 

 try, but comparative analyses of the cement used in the building 

 of the pyramid of Cheops and the modern cement plaster show 

 a remarkable similarity in composition. Whether these two 

 cements had the same chemical composition when prepared for 

 use is a question, as slightly overburned or underburned gypsum 

 will absorb water and return to the original condition, but much 

 more slowly than gypsum that is properly burned. It is sup- 

 posed by some that the cementing material of the pyramid of 

 Cheops was slower setting than the cement plasters. 



The difference between ordinary plaster of paris and a cement 

 plaster is brought about by the addition of some retarding 

 material to the plaster of paris, so that it will not set so soon, 

 ordinary plaster of paris requiring only a few minutes to become 

 hard, while a cement plaster requires from two to 24 hours to 

 become thoroughly hard. 



It is of interest to note that, whereas New York State plaster 

 of paris was considered of no value but a few years ago, at the 

 present time most of the mills have difficulty in filling their 

 orders. With the increased use of gypsum cement plaster, the 



