GYPSUM 413 



Silicated plaster is formed by spon<Tinp^ the surfncc of 

 plaster casts with a solution forniod by iirst addiu}.'; wlicy fn^e 

 from fatty matter, to a potash lye solution made by addin*^ 1 

 part of potash to 5 parts of water, and aftenvards mixing 1 

 parts of this with a simple solution of potassium silicate. 



Stearin melted at not too hi^h a temperature has been 

 employed as a bath in which i^laster casts are immersed. 



Landrin found that lime had great influence on plasters. 

 By mixing lime with the plaster in different proportions, not 

 to exceed 10 per cent, he obtained plaster which set regularl\-, 

 became very hard, and took a high polish. 



A large number of patents have been issued for retarding 

 compounds and admixtures, and for prepared plasters, as well 

 as for processes of manufacture and for hardening gjq)sum, 

 and a digest of the same will be found in an appendix. There 

 have also been issued some 280 or more patents for improve- 

 ments in the arts involving the use of g\^)sum or plaster of 

 Paris in the manufacture of artificial stone, wall and roofing 

 cements, pavements, crayons, blackboards, heat insulating 

 composition, etc. 



