MANUFACTURE OF PLASTERS. 55 



Inspection of the analyses quoted in Tables 8 and 9 will show that 

 the rock gypsum used at plaster plants is usually very pure. Until 

 very recently no attempt has been made to utilize the impure gypsum 

 rock which forms such a large proportion of the New York deposits , 

 though there is no technologic reason for not using it. The analyses 

 of gypsite or gypsum earth, on the other hand, are mostly representa- 

 tive of very impure materials, carrying large percentages of sand, clay, 

 and fragments of limestone. The presence of these impurities in the 

 natural raw material is a matter of technologic importance, for the 

 calcined plaster made from such impure materials is naturally very 

 slow setting. 



References on plaster-manufacture. The following papers deal 

 largely with the manufacturing side of the gypsum industry. 



Crane, W. R. Mining and milling of gypsum in Kansas Engineering and 



Mining Journal, Nov. 9, 1901. 

 Crane, W R. The gypsum plaster industry of Kansas. Engineering and 



Mining Journal, vol. 77, pp. 442-445. 1904. 

 Grimsley G. P., and Bailey, E. H. S. Special report on gypsum and gypsum 



cement plasters. Vol. 5, University Geological Survey of Kansas, 



183 pp. 1899. 

 Grimsley, G. P. A preliminary report on the gypsum deposits of Michigan. 



Ann. Rep. Michigan Geological Survey for 1902, pp. 4-10. 1903. 

 Parsons, A. L. Recent developments in the gypsum industry in New York 



State. 20th Ann. Rep. New York State Geologist, pp. 177-183. 1902. 

 Slosson, E. E., and Moudy, R. B. The Laramie cement plaster. 10th Ann, 



Rep. Wyoming College of Agricultural and Mechanics. 

 Wilder, F. A. Geology of Webster County, Iowa. Vol. 12, Reports Iowa 



Geological Survey, pp. 63-235. 1902. 

 Wilder, F. A. The gypsum industry of Germany. Vol. 12, Reports Iowa 



Geological Survey, pp. 192-223. 1902. 



Wilder, F. A. Present and future of the American gypsum industry. En- 

 gineering and Mining Journal, vol. 74, pp. 276-278. 1902. 

 Wilkinson, P. The technology of cement plaster. Trans. Amer. Inst. Mining 



Engrs., vol. 27, pp. 508-519. 



