44 



CEMENTS, LIMES, AND PLASTERS. 



the water determinations the raw material (gypsum earth) carried a 

 very large percentage of moisture in addition to its necessary water 

 of crystallization. An analysis of the finished product, given below, 

 shows that it is made from a very impure gypsum: 



ANALYSIS OF LARAMIE PLASTER. 



Lime sulphate (CaSO 4 ) 73 . 73% 



Lime carbonate (CaC0 3 ) 7.86% 



Lime (CaO) 2.35% 



Magnesium carbonate (MgCO 3 ) 3.04% 



Silica (SiO 2 ) 5.50% 



Alumina (A1 2 O 8 ) . 59% 



Water (H 2 O) 6.93% . 



Inspection of this analysis also proves that the plaster still carries 

 a little more water than is theoretically correct. If these various points 

 be borne in mind, the temperature determinations given below will 

 prove of value. 



TABLE 6. 

 TEMPERATURES IN CEMENT-PLASTER MANUFACTURE. 



Actual equipment of kettle-process plants. Plans of two kettle- 

 process plants are given in Figs. 12 and 13. The following data, giving 

 the actual equipments of a number of plaster-plants in the United States, 

 will serve to give a good idea of the relation of crushing machinery to 

 number of kettles: 



Plant No. 1. (a) 2 Butterworth & Lowe nippers. 

 (6) 2 Butterworth & Lowe crackers. 



(c) 4 runs of 4-foot buhrstones and 1 Sturtevant vertical rock emery 



mill. 



(d) 4 10-foot kettles holding 10 tons each. 



(e) 8 runs of small buhrstones for regrinding finer grades of plaster. 

 Plant No. 2. (a) 1 nipper. 



(6) 1 cracker. 



(c) 4 runs of buhrstones. 



(d) 3 10-foot kettles. 



