128 NEW YORK STATE MUSEUM 



sulfid is reduced to a minimum. The entire inner chamber is 

 divided into two unequal parts bj an arch, situated about a foot 

 from the bottom. The upper part, into which the gypsum is 

 introduced, is provided with eight draft holes. The lower cham- 

 ber, or fire surface, is situated in front of the kiln. The draft 

 channel terminates in the ash pit under the grate, on which a 

 coal fire is made. 



The flame enters below the perforated arch, where it is uni- 

 formly distributed over the whole area of the kiln in an upward 

 direction through the gypsum, and makes its escape through 

 apertures. The capacity of this kiln is given as 220 cubic feet 

 of gypsum. Dumesnil's oven resembles Scannegatty's in form 

 and in the manner in which the heat is applied, but would seem 

 to be less economical of labor, though more heat is saved. 



After the gypsum was calcined by any of the foregoing 

 processes, it was reduced partially to powder, but the bulk of it 

 had to be ground and sifted to separate the coarse particles. 



In New York there are 18 mills engaged in the manufacture of 

 land plaster and in the manufacture of plaster of paris from 

 New York State g}^sum. Two processes, the Cummer and the 

 kettle, are employed in the manufacture of plaster of paris. So 

 far as the land plaster is concerned, the process by which it is 

 made is the same as the first steps in the kettle process of making 

 plaster of paris. 



The machinery used by most of the mills is made by Butter- 

 worth & Lowe of Grand Rapids Mich., and F. D. Cummer of 

 Cleveland O. 



Kettle process. As a rule, the crusher, which is usually an 

 ordinary jaw crusher, is placed on the ground floor of the mill, so 

 that the rock may be thrown directly from the wagon or car intto 

 the hopper. Pieces up to about a foot in diameter are reduced 

 in this crusher to pieces of about 2 or 3 inches in (^iameter and 

 are then taken to the nipper. 



The nipper resembles an old-fashioned cofl'ee mill, to a certain 

 extent. The upper part, however, consists of a corrugated hopper 

 in which a corrugated cone rotates, crushing the pieces of gypsum 



