Polytechnic Association Proceedings. 577 



York, extending into Ontario county on one side, and Onondaga 

 county on the other. Large quantities are ground and sold under 

 the name of "plaster," or "plaster of Paris." Gypsum is formed 

 by the action of sulphuric acid on limestone, the sulphuric acid 

 being derived from sulphurets, or volcanic vapor. Gypsum is a 

 very abundant mineral, but is found most extensively at Windson, 

 Harts county. Nova Scotia, from which place 100,000 tons of plas- 

 ter are exported annually. The deposit is about one hundred and 

 fifty feet wide and is probably fifty miles in length. 



Prof. Vanderweyde remarked that Dr. Benjamin Franklin was 

 the first to use gypsum as a fertilizer. He used to form the letters 

 with it in the ground to spell the word " plaster," which the 

 increased vegetable growth afterwards made visible. It is well 

 known that soil that is deficient in lime will not produce grain. 



Dr. D- D. Parmelee said the utility of gypsum was due to its 

 holding moisture and giving it out when wanted. It holds water 

 for a long time. Lime would part with it very quick. 



Dr. Vanderweyde remarked that those who cast in plaster of 

 Paris mix just enough for present use, as it dries very quickly. It 

 can be prevented from setting quick by the use of lime, but this 

 causes it to crack. Plaster of Paris does not shrink at all. 



Dr. Feuchtwanger agreed with Dr. Parmelee as to the water- 

 absorbing qualities of plaster of Paris, and this constituting its 

 value as a fertilizer. 



Mr. Hilton held that the great virtue of plaster consisted in it^ 

 power of absorbing ammonia and giving it out to the plant. 



The Chairman said chemists have not made it plain in what the 

 acknowledged merit of gypsum, or natural sulphate of lime, as a 

 fertilizer, consists. It is a very important question, and he pro- 

 posed that it be resumed at the next meeting. Adjourned. 



May 16, 1867. 

 Prof. S. D. Tillman in the chair; J. Wyatt Reid, Esq., Secretary. 



The Chairman opened the proceedings by reading the following 

 summary of scientific news: 



PROCESS OF BLEACHmG GUM. 



Picciotto states, that mucilage may be completely decolorized 

 by means of recently precipitated gelatinous alumina, which fixes 

 [Inst.] 37 



