124 NEW YORK STATE MUSEUM 



glue, and fiber is added to give strength and toughness, while 

 strips of wood are laid crosswise in the back of the larger pieces 

 to give rigiditj and in some cases to afford a better means of 

 fastening the piece to the wall or ceiling, 



A more recent development of the gypsum industry is the 

 manufacture of wall boards made from alternating layers of 

 paper and plaster of paris. The process of manufacture con- 

 sists in spreading the properly moistened plaster of paris on 

 the surface of a sheet of building paper, above the layer of 

 gypsum is then placed another sheet of paper, and the two 

 layers of paper and the one of gypsum are then passed between 

 rolls, after which another layer of gypsum is spread above the 

 second sheet of paper, a third sheet of paper is added and the 

 rolling process continued. This operation may be repeated an 

 indefinite number of times, but the usual practice is to have 

 from five to seven layers of gypsum. When the board has passed 

 from the machine where it is made, it is conveyed down a long 

 table, where it becomes partially hard and is cut into the proper 

 size for use. In order to give the material a chance to dry with- 

 out warping, it is suspended from supports from the ceiling. 

 When dry, the boards may be nailed to studs and rafters in the 

 same way as boards or lath. 



In the manufacture of glass, gypsum takes a very important 

 part. In the uncalcined state it is said to be used as a con- 

 stituent of certain kinds of glass. Its most important use, 

 however, is in the calcined state, when it is used in plate glass 

 factories to form a bed on which the glass is placed for polish- 

 ing. In this way the strain is taken from the glass and there is 

 little liability of breakage. 



In monumental work, plaster of paris finds a similar use 

 when it is placed about the stone to be polished, to form a bed 

 for catching the water and polishing material. 



The use of plaster of paris as a flux^ is bat little known, but in 

 melting brass it is found to be superior to any known flux. It 



^ Sperry, E. S. AlumiDum World, March, 1902. 



